Thus far, the most fruitful approach has been to examine life on our own planet.  However, even in our own backyard, it is difficult to determine life's origins because it began at least 3.5 billion years ago.  We know that life began at least 3.5 billion years ago, because that is the age of the oldest rocks with fossil evidence of life on earth.  These rocks are rare because subsequent geologic processes have reshaped the surface of our planet, often destroying older rocks while making new ones.  Nonetheless, 3.5 billion year old rocks with fossils can be found in Africa and Australia.  They are usually a mix of solidified volcanic lavas and sedimentary cherts.  The fossils occur in sedimentary cherts.

Our progress on this question has been impeded by a formidable cognitive barrier. Because we perceive a deep gap when we think about the difference between inorganic matter and life, we feel that nature must have made a big leap to cross that gap. This point of view has led to searches for ways large and complex molecules could have formed early in Earth’s history, a daunting task. The essential problem is that in modern living systems, chemical reactions in cells are mediated by protein catalysts called enzymes. The information encoded in the nucleic acids DNA and RNA is required to make the proteins; yet the proteins are required to make the nucleic acids. Furthermore, both proteins and nucleic acids are large molecules consisting of strings of small component molecules whose synthesis is supervised by proteins and nucleic acids. We have two chickens, two eggs, and no answer to the old problem of which came first.

In this article we present a view gaining attention in the origin-of-life community that takes the question out of the hatchery and places it squarely in the realm of accessible, plausible chemistry. As we see it, the early steps on the way to life are an inevitable, incremental result of the operation of the laws of chemistry and physics operating under the conditions that existed on the early Earth, a result that can be understood in terms of known (or at least knowable) laws of nature. As such, the early stages in the emergence of life are no more surprising, no more accidental, than water flowing downhill.

The new approach requires that we adopt new ways of looking at two important fields of science. As we will see below, we will have to adjust our view of both cellular biochemistry and thermodynamics. Before we talk about these new ideas, however, it will be useful to place them in context by outlining a little of the history of research on the origin of life.

Electric sparks can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen, as was shown in the famous Miller-Urey experiment reported in 1953, suggesting that lightning might have helped create the key building blocks of life on Earth in its early days. Over millions of years, larger and more complex molecules could form. Although research since then has revealed the early atmosphere of Earth was actually hydrogen-poor, scientists have suggested that volcanic clouds in the early atmosphere might have held methane, ammonia and hydrogen and been filled with lightning as well.

Or could simple clay have fueled life’s beginning? Read on to find out.

Molecules of life met on clay-The first molecules of life might have met on clay, according to an idea elaborated by organic chemist Alexander Graham Cairns-Smith at the University of Glasgow in Scotland. These surfaces might not only have concentrated these organic compounds together, but also helped organize them into patterns much like our genes do now.

The main role of DNA is to store information on how other molecules should be arranged. Genetic sequences in DNA are essentially instructions on how amino acids should be arranged in proteins. Cairns-Smith suggests that mineral crystals in clay could have arranged organic molecules into organized patterns. After a while, organic molecules took over this job and organized themselves.

Or maybe life began at the bottom of the sea. Keep going to learn how.

Since 1953, we have found many of the same simple organic molecules in meteorites, comets and even interstellar gas clouds. Far from being special, then, the simplest of the molecules we find in living systems—life’s building blocks—seem to be quite common in nature. To many, the real question was how these basic building blocks got put together into living systems, and, equally important, how the molecules that led to modern life were selected out of the messy molecular milieu in which they arose.

The ubiquity of simple molecules suggested an appealing scenario that had a profound effect on the way investigators approached the origin of life throughout the last half of the 20th century. The scenario went like this: After the Earth cooled enough to allow oceans to form, the Miller-Urey process or something like it produced a rain of organic matter. In a relatively short time, the ocean became a broth of these molecules, and given enough time, the right combination of molecules came together by pure chance to form a replicating entity of some kind that evolved into modern life.

Scientists called this scenario the Oparin-Haldane conjecture, but it was given a provocative nickname that endures in the popular consciousness—Primordial Soup.

The essential legacy of the Primordial Soup was twofold: It simplified the notion of the origin of life to a single pivotal event, and then it proposed that that event—the step that occurred after the molecules were made—was a result of chance. In the standard language, life is to be seen, in the end, as a “frozen accident.” In this view, many fundamental details about the structure of life are not amenable to explanation. The architecture of life is just one of those things. Although many modern theories are less extreme than this, frozen-accident thinking still influences what some of us ask about the origin of life and how we prioritize our experiments.

Renee Antonette Olita and Trisha M. Espeja

Electric sparks can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen, as was shown in the famous Miller-Urey experiment reported in 1953, suggesting that lightning might have helped create the key building blocks of life on Earth in its early days. Over millions of years, larger and more complex molecules could form. Although research since then has revealed the early atmosphere of Earth was actually hydrogen-poor, scientists have suggested that volcanic clouds in the early atmosphere might have held methane, ammonia and hydrogen and been filled with lightning as well.

The first molecules of life might have met on clay, according to an idea elaborated by organic chemist Alexander Graham Cairns-Smith at the University of Glasgow in Scotland. These surfaces might not only have concentrated these organic compounds together, but also helped organize them into patterns much like our genes do now.

The main role of DNA is to store information on how other molecules should be arranged. Genetic sequences in DNA are essentially instructions on how amino acids should be arranged in proteins. Cairns-Smith suggests that mineral crystals in clay could have arranged organic molecules into organized patterns. After a while, organic molecules took over this job and organized themselves.

The deep-sea vent theory suggests that life may have begun at submarine hydrothermal vents spewing key hydrogen-rich molecules. Their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents, rich in chemical and thermal energy, sustain vibrant ecosystems.

Ice might have covered the oceans 3 billion years ago, as the sun was about a third less luminous than it is now, scientists say. This layer of ice, possibly hundreds of feet thick, might have protected fragile organic compounds in the water below from ultraviolet light and destruction from cosmic impacts. The cold might have also helped these molecules to survive longer, allowing key reactions to happen. 

Nowadays DNA needs proteins in order to form, and proteins require DNA to form, so how could these have formed without each other? The answer may be RNA, which can store information like DNA, serve as an enzyme like proteins, and help create both DNA and proteins. Later DNA and proteins succeeded this "RNA world," because they are more efficient.

RNA still exists and performs several functions in organisms, including acting as an on-off switch for some genes. The question still remains how RNA got here in the first place. And while some scientists think the molecule could have spontaneously arisen on Earth, others say that was very unlikely to have happened. Other nucleic acids other than RNA have been suggested as well, such as the more esoteric PNA or TNA.

Instead of developing from complex molecules such as RNA, life might have begun with smaller molecules interacting with each other in cycles of reactions. These might have been contained in simple capsules akin to cell membranes, and over time more complex molecules that performed these reactions better than the smaller ones could have evolved, scenarios dubbed "metabolism-first" models, as opposed to the "gene-first" model of the "RNA world" hypothesis.

Perhaps life did not begin on Earth at all, but was brought here from elsewhere in space, a notion known as panspermia. For instance, rocks regularly get blasted off Mars by cosmic impacts, and a number of Martian meteorites have been found on Earth that some researchers have controversially suggested brought microbes over here, potentially making us all Martians originally. Other scientists have even suggested that life might have hitchhiked on comets from other star systems. However, even if this concept were true, the question of how life began on Earth would then only change to how life began elsewhere in space.

At the time it was widely agreed that stromatolites were oldest known lifeform on Earth which had left a record of its existence. Therefore, if life originated on Earth, this happened sometime between 4.4 billion years ago, when water vapor first liquefied, and 3.5 billion years ago.

Fossil evidence informs most studies of the origin of life. The age of the Earth is about 4.54 billion years; the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago.

Radioactive Decay studies of rocks

Based on this it was revealed that Earth is around 4.5 billion years old- 1 billion years older than the oldest fossils

Extra Terrestrial Origin

Hypothesis explains that life originated from another planet outside the Solar System

Panspermia

This theory presumes that the "seed" of life exists all over the universe and can be propagated through the space, and that life on Earth originated from those seeds.

Divine Creation

Theory where many people believed that life was put on early Earth by divine forces. Creation theories are common to many of the world's religions and cultures.

Origin from Non-Living Matter

Belief that life arose on Earth from inanimate matter after Earth had cooled. Random events produced stable molecules that could self-replicate. Natural selection favored changes in the rate or reproduction which eventually led to the first cell.

Stanley Miller and Harold Urey

Performed an experiment that replicated the early Earth conditions and provided proof of amino acids and other molecules could be formed.

Hydrogen, Carbon Dioxide, Methane, Water Vapor, Nitrogen, Ammonia and Carbon Monoxide

Simple molecules that were probably present in the early Earth's atmosphere

Amino Acids

The building blocks of proteins

Cell Membrane

Seperates the cell from its environment which contains lipids

Coacervates

When lipids mix with water they form bubbles that are called?

Prokaryotes

Scientists believed that the first cells were the?

Prokaryotes

Organisms whose cells have no nucleus

Anaerobic

The first prokaryotes

Anaerobic

They do not need and could not tolerate oxygen

4.5 Billion Years Old

Estimated age of the Earth

Eubacteria

(True bacteria) Most living bacteria including those that causes diseases and decomposition

Archaebacteria

(Ancient bacteria) rare and are found mainly in hostile environments where conditions resemble those of early Earth (salty lakes, hot springs, swamps, ocean floors)

Eukaryotes

More complex life formed-appeared in the fossil record which are known as?

Plants and fungi

The first living things to populate the surface of the land

Arthropods

Animals with hard covering and jointed legs and the first animals to live on water

0.5 BYA

Rapid diversification of animals, plants and fungi appear, origin of the humans (about 2 million years ago)

1.0 BYA

Earliest animals; first multicellular organisms; diverse protists

1.5 BYA

First prokaryotes

2.0 BYA

Diverse and abundant bacteria

2.5 BYA

Photosynthesis begins

3.0 BYA

Bacteria diversity

3.5 BYA

First bacteria appeared

4.0 BYA or 3.8 billion years ago

Oldest Rocks

4.5 BYA

Earth forms

The earliest signs of life on a young Earth, around 3.5 billion years ago, have generally come from the ocean in the form of fossilized microbes within ancient rock. Now, scientists working in the Barberton Greenstone Belt in South Africa—where some of the oldest rocks on Earth are preserved—find evidence of terrestrial microbial life that they estimate is about 3.22 billion years old.

Researchers have found more fossil evidence of the earliest microbial life in shallow, marine deposits, which supports the dominant theory that before 3 billion years ago, most of the Earth consisted of oceans interspersed with volcanic islands. Evidence for life on land has so far been harder to come by. Part of the reason is that ancient marine rocks appear to be better preserved than terrestrial sediments.

Since 1953, we have found many of the same simple organic molecules in meteorites, comets and even interstellar gas clouds. Far from being special, then, the simplest of the molecules we find in living systems—life’s building blocks—seem to be quite common in nature. To many, the real question was how these basic building blocks got put together into living systems, and, equally important, how the molecules that led to modern life were selected out of the messy molecular milieu in which they arose.

The ubiquity of simple molecules suggested an appealing scenario that had a profound effect on the way investigators approached the origin of life throughout the last half of the 20th century. The scenario went like this: After the Earth cooled enough to allow oceans to form, the Miller-Urey process or something like it produced a rain of organic matter. In a relatively short time, the ocean became a broth of these molecules, and given enough time, the right combination of molecules came together by pure chance to form a replicating entity of some kind that evolved into modern life.

But that discovery, based on an analysis of primordial rocks in Greenland, has now been challenged, with another team of researchers arguing in a study published Wednesday that the structures presented as proof of microbial activity were, in fact, geologically forged by underground heat and pressure.

The truth hinges on whether the cone-shaped formations in question are genuine stromatolites, layered structures left in the wake of water-dwelling microorganisms.

Previously, the earliest confirmed stromatolites were found in 3.45-billion year old rocks in Australia.

Being able to accurately date the first stirrings of life on our young planet—roughly a billion years old at the time—has important implications for understanding how it emerged and evolved.

Writing in the journal Nature, Abigail Allwood of the California Institute of Technology and colleagues analysed the three-dimensional shape of the disputed formations, along with their orientation in space and chemical composition.

The 3-D view led them to conclude that the alleged fossils lacked internal layers, a signature trait of stromatolites. Upon closer examination, the cone-like shapes were shown to be ridges that typically arise over millions of years through a natural deforming process called metamorphism.

Also missing, they said, were the chemical traces of microbe activity.

"We believe that the current evidence does not support the interpretation of these structures as 3.7 billion-year-old stromatolites," Allwood's team concluded.

Their analysis, the study continued, should also serve as a "cautionary tale" in interpreting rock formations in the search for life on Mars.

Mark Van Zuilen, a geomicrobiologist at the Institut de Physique du Globe in Paris, said the reassessment is convincing, and suggests the Australian stromatolites should regain their status as the earliest confirmed proof of life on Earth.

"These observations provide strong evidence for physical rock deformation and therefore offer a non-biological explanation for the observed structures," he commented in Nature.

Allen Nutman, a professor at the University of Wollongong in Australia and lead researcher on the 2016 study, was not available for comment.

Geological evidence has hinted that life existed in the oceans as far back as 3.8 billion years ago. But signs of terrestrial life have been rarer — possibly because much of the planet might have been under water until 3 billion years ago. [In Images: The Oldest Fossils on Earth]

The idea that life made landfall this early in Earth's history has been around for decades, said Hugo Beraldi Campesi, a geobiologist at the National Autonomous University of Mexico, who was not involved in the new research. "The problem was always the lack of hard evidence — until now." The new discovery adds to the growing body of evidence that the continents have harbored life for a long time, he added.

The researchers, led by Martin Homann, a sedimentologist at the European Institute for Marine Studies, discovered the fossilized microbes on the side of a rocky cliff in the Barberton Makhonjwa Mountains of eastern South Africa, home to some of the world's oldest geological features. The fossils are part of a chunk of rock called the Moodies Group, which represents one of the world's oldest shorelines, Lalonde said.

The microbes are extremely well-preserved, he said, showing thick sheets that blanket pebbles, a sign that the critters lived on an ancient riverbed — a terrestrial environment — rather than a sandy beach. Ripple-like features suggest that water flowed in one direction in this area, further evidence that the microbes lived along a river or, perhaps, an alluvial fan. That's a geological feature formed when runoff flows outward in the shape of a fan.


Historical development

Radio active decays studies of rocks
Extra terrestrial origin
Divine creation
Origin from non living matter
Stanley Miller and Haroid Urey
Hydrogen, CO2, Methane, water vapor, nitrogen, ammonia, and carbon monoxide
Amino acids
Cell membrane
Coacerva waters
Prokaryotes
Anaerobic 
5.6 billion years old
Eubacteria 
Archaebacteria 
Eukaryotes
Plants and fungi
Anthropoids
0.5 BYA
1.0 BYA
1.5 BYA
2.0 BYA
2.5 BYA
3.0 BYA
3.5 BYA
4.0 BYA
4.5 BYA

Perhaps no other system is as unique to planet Earth as the biosphere, which includes all forms of life. Life occurs nearly everywhere on, above, and even under the surface of the planet. In terms of actual biomass, it is likely that microbes that live beneath the surface exceed that of all the surface life, plants, and animals. Some microbes survive in the upper atmosphere as high as 25 km and as deep in the crust as several kilometers. The temperature range of life continues to increase as we learn more about microbes, which today is from about 120 °C around thermal springs to as low as − 20 °C in some glacial environments. The origin of life is a subject of on-going research and is considered one of the great events in Earth's history. One of the exciting questions is whether life actually formed here on Earth or if it was transferred here from elsewhere in the solar system. In this chapter, we will consider this as well as other questions regarding the origin and evolution of life and the great mass extinctions of the past. 
Previous earliest

At the time it was widely agreed that stromatolites were oldest known lifeform on Earth which had left a record of its existence. Therefore, if life originated on Earth, this happened sometime between 4.4 billion years ago, when water vapor first liquefied, and 3.5 billion years ago. The first molecules of life might have met on clay, according to an idea elaborated by organic chemist Alexander Graham Cairns-Smith at the University of Glasgow in Scotland. These surfaces might not only have concentrated these organic compounds together, but also helped organize them into patterns much like our genes do now.

The main role of DNA is to store information on how other molecules should be arranged. Genetic sequences in DNA are essentially instructions on how amino acids should be arranged in proteins. Cairns-Smith suggests that mineral crystals in clay could have arranged organic molecules into organized patterns. After a while, organic molecules took over this job and organized themselves.

Or maybe life began at the bottom of the sea.

1.It started with an electric spark

Lightning may have provided the spark needed for life to begin.

Electric sparks can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen, as was shown in the famous Miller-Urey experiment reported in 1953, suggesting that lightning might have helped create the key building blocks of life on Earth in its early days. Over millions of years, larger and more complex molecules could form. Although research since then has revealed the early atmosphere of Earth was actually hydrogen-poor, scientists have suggested that volcanic clouds in the early atmosphere might have held methane, ammonia and hydrogen and been filled with lightning as well.

2.Molecules of life met on clay

The first molecules of life might have met on clay, according to an idea elaborated by organic chemist Alexander Graham Cairns-Smith at the University of Glasgow in Scotland. These surfaces might not only have concentrated these organic compounds together, but also helped organize them into patterns much like our genes do now.

The main role of DNA is to store information on how other molecules should be arranged. Genetic sequences in DNA are essentially instructions on how amino acids should be arranged in proteins. Cairns-Smith suggests that mineral crystals in clay could have arranged organic molecules into organized patterns. After a while, organic molecules took over this job and organized themselves.

3.Life began at deep-sea vents

The deep-sea vent theory suggests that life may have begun at submarine hydrothermal vents spewing key hydrogen-rich molecules. Their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents, rich in chemical and thermal energy, sustain vibrant ecosystems.

4.Life had a chilly start.

Ice might have covered the oceans 3 billion years ago, as the sun was about a third less luminous than it is now, scientists say. This layer of ice, possibly hundreds of feet thick, might have protected fragile organic compounds in the water below from ultraviolet light and destruction from cosmic impacts. The cold might have also helped these molecules to survive longer, allowing key reactions to happen.

5.The answer lies in understanding DNA formation

Nowadays DNA needs proteins in order to form, and proteins require DNA to form, so how could these have formed without each other? The answer may be RNA, which can store information like DNA, serve as an enzyme like proteins, and help create both DNA and proteins. Later DNA and proteins succeeded this "RNA world," because they are more efficient.

6.Life had simple beginnings

Instead of developing from complex molecules such as RNA, life might have begun with smaller molecules interacting with each other in cycles of reactions. These might have been contained in simple capsules akin to cell membranes, and over time more complex molecules that performed these reactions better than the smaller ones could have evolved, scenarios dubbed "metabolism-first" models, as opposed to the "gene-first" model of the "RNA world" hypothesis.

7.Life was brought here from elsewhere in space

Perhaps life did not begin on Earth at all, but was brought here from elsewhere in space, a notion known as panspermia. For instance, rocks regularly get blasted off Mars by cosmic impacts, and a number of Martian meteorites have been found on Earth that some researchers have controversially suggested brought microbes over here, potentially making us all Martians originally. Other scientists have even suggested that life might have hitchhiked on comets from other star systems. However, even if this concept were true, the question of how life began on Earth would then only change to how life began elsewhere in space.

Life has developed from those simple organisms, exploding into more than 1.3-million documented species of living things on Earth today. Scientists estimate there are between 30-million and 100–million species on Earth, though only about 1.3–million of these have been documented.

The development of life on Earth as we know it has generally been gradual, although there have been periods of rapid change. The most prolific profusion of species has occurred during the last eighth of Earth’s history, known as the Phanerozoic Era, within the past 543-million years.

On the other hand, the scientific trend toward understanding biological phenomena at the molecular level led authors like Troland, Muller, and others to propose that single molecules or viruses represented primordial living systems. The contrast between these opposing views on the origin of life represents not only contrasting views of the nature of life itself, but also major ideological discussions that reached a surprising intensity in the years following Stanley Miller’s seminal result which showed the ease with whichorganic compounds of biochemical significance could be synthesized under putative primitive conditions. In fact, during the years following the Miller experiment, attempts to understand the origin of life were strongly influenced by research on DNA replication and protein biosynthesis, and, in socio-political terms, by the atmosphere created by Cold War tensions.

The catalytic versatility of RNA molecules clearly merits a critical reappraisal of Muller’s viewpoint. However, the discovery of ribozymes does not imply that autocatalytic nucleic acid molecules ready to be used as primordial genes were floating in the primitive oceans, or that the RNA world emerged completely assembled from simple precursors present in the prebiotic soup. The evidence supporting the presence of a wide range of organic molecules on the primitive Earth, including membrane-forming compounds, suggests that the evolution of membrane-bounded molecular systems preceded cellular life on our planet, and that life is the evolutionary outcome of a process, not of a single, fortuitous event.

It is generally assumed that early philosophers and naturalists appealed to spontaneous generation to explain the origin of life, but in fact, the possibility of life emerging directly from nonliving matter was seen at first as a nonsexual reproductive mechanism. This changed with the transformist views developed by Erasmus Darwin, Georges Louis Leclerc de Buffon, and, most importantly, by Jean-Baptiste de Lamarck, all of whom invoked spontaneous generation as the mechanism that led to the emergence of life, and not just its reproduction. “Nature, by means of of heat, light, electricity and moisture”, wrote Lamarck in 1809, “forms direct or spontaneous generation at that extremity of each kingdom of living bodies, where the simplest of these bodies arefound”.

Like his predecessors, Charles Darwin surmised that plants and animals arose naturally from some primordial nonliving matter. As early as 1837 he wrote in his Second Notebook that “the intimate relation of Life with laws of chemical combination, & the universality of latter render spontaneous generation not improbable.” However, Darwin included few statements about the origin of life in his books. He avoided the issue in the Origin of Species, in which he only wrote “… I should infer from analogy that probably all organic beings which have ever lived on this Earth have descended from some one primordial form, into which life was first breathed” (Peretó et al. 2009).

Darwin added few remarks on the origin of life his book, and his reluctance surprised many of his friends and followers. In his monograph on the radiolaria, Haeckel wrote “The chief defect of the Darwinian theory is that it throws no light on the origin of the primitive organism—probably a simple cell—from which all the others have descended. When Darwin assumes a special creative act for this first species, he is not consistent, and, I think, not quite sincere …” (Haeckel 1862).

Twelve years after the first publication of the Origin of Species, Darwin wrote the now famous letter to his friend Hooker in which the idea of a “warm little pond” was included. Mailed on February 1st, 1871, it stated that “It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and Oh! what a big if!) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts—light, heat, electricity &c. present, that a proteine compound was chemically formed, ready to undergo still morecomplex changes, at the present day such matter wd be instantly devoured, or absorbed, which would not have been the case before living creatures were formed.” Although Darwin refrained from any further public statements on how life may have appeared, his views established the framework that would lead to a number of attempts to explain the origin of life by introducing principles of historical explanation (Peretó et al. 2009). Here I will describe this history, and how it is guiding current research into the question of life’s origins.

Our progress on this question has been impeded by a formidable cognitive barrier. Because we perceive a deep gap when we think about the difference between inorganic matter and life, we feel that nature must have made a big leap to cross that gap. This point of view has led to searches for ways large and complex molecules could have formed early in Earth’s history, a daunting task. The essential problem is that in modern living systems, chemical reactions in cells are mediated by protein catalysts called enzymes. The information encoded in the nucleic acids DNA and RNA is required to make the proteins; yet the proteins are required to make the nucleic acids. Furthermore, both proteins and nucleic acids are large molecules consisting of strings of small component molecules whose synthesis is supervised by proteins and nucleic acids. We have two chickens, two eggs, and no answer to the old problem of which came first.

In this article we present a view gaining attention in the origin-of-life community that takes the question out of the hatchery and places it squarely in the realm of accessible, plausible chemistry. As we see it, the early steps on the way to life are an inevitable, incremental result of the operation of the laws of chemistry and physics operating under the conditions that existed on the early Earth, a result that can be understood in terms of known (or at least knowable) laws of nature. As such, the early stages in the emergence of life are no more surprising, no more accidental, than water flowing downhill.

The new approach requires that we adopt new ways of looking at two important fields of science. As we will see below, we will have to adjust our view of both cellular biochemistry and thermodynamics. Before we talk about these new ideas, however, it will be useful to place them in context by outlining a little of the history of research on the origin of life

Electric sparks can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen, as was shown in the famous Miller-Urey experiment reported in 1953, suggesting that lightning might have helped create the key building blocks of life on Earth in its early days. Over millions of years, larger and more complex molecules could form. Although research since then has revealed the early atmosphere of Earth was actually hydrogen-poor, scientists have suggested that volcanic clouds in the early atmosphere might have held methane, ammonia and hydrogen and been filled with lightning as well.

2. Molecules of life met on clay
-The first molecules of life might have met on clay, according to an idea elaborated by organic chemist Alexander Graham Cairns-Smith at the University of Glasgow in Scotland. These surfaces might not only have concentrated these organic compounds together, but also helped organize them into patterns much like our genes do now.

The main role of DNA is to store information on how other molecules should be arranged. Genetic sequences in DNA are essentially instructions on how amino acids should be arranged in proteins. Cairns-Smith suggests that mineral crystals in clay could have arranged organic molecules into organized patterns. After a while, organic molecules took over this job and organized themselves.

3.Life began at deep-sea vents
-The deep-sea vent theory suggests that life may have begun at submarine hydrothermal vents spewing key hydrogen-rich molecules. Their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents, rich in chemical and thermal energy, sustain vibrant ecosystems.

4. Life had a chilly start
-Ice might have covered the oceans 3 billion years ago, as the sun was about a third less luminous than it is now, scientists say. This layer of ice, possibly hundreds of feet thick, might have protected fragile organic compounds in the water below from ultraviolet light and destruction from cosmic impacts. The cold might have also helped these molecules to survive longer, allowing key reactions to happen. [Related: The Ingredients of Life]

5. The answer lies in understanding DNA formation
-
Nowadays DNA needs proteins in order to form, and proteins require DNA to form, so how could these have formed without each other? The answer may be RNA, which can store information like DNA, serve as an enzyme like proteins, and help create both DNA and proteins. Later DNA and proteins succeeded this "RNA world," because they are more efficient.

6.Life had simple beginnings
-Instead of developing from complex molecules such as RNA, life might have begun with smaller molecules interacting with each other in cycles of reactions. These might have been contained in simple capsules akin to cell membranes, and over time more complex molecules that performed these reactions better than the smaller ones could have evolved, scenarios dubbed "metabolism-first" models, as opposed to the "gene-first" model of the "RNA world" hypothesis.

7. Life was brought here from elsewhere in space
-Perhaps life did not begin on Earth at all, but was brought here from elsewhere in space, a notion known as panspermia. For instance, rocks regularly get blasted off Mars by cosmic impacts, and a number of Martian meteorites have been found on Earth that some researchers have controversially suggested brought microbes over here, potentially making us all Martians originally. Other scientists have even suggested that life might have hitchhiked on comets from other star systems. However, even if this concept were true, the question of how life began on Earth would then only change to how life began elsewhere in space.


Evidences of life
About 3.22 billion years ago, slimy layers of microbes coated pebbles in what was perhaps an ancient riverbed. Those ancient microbial mats, preserved for eons and only recently discovered in South Africa, may be the oldest fossil evidence of life on land, according to a new study.

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The ancient evidence of terrestrial life is about a half billion years older than the previous record holder — fossilized remains of microbes found decades ago in South Africa and Australia, said Stefan Lalonde, a geochemist from the European Institute for Marine Studies in France and a co-author of the new study, published July 23 in the journal Nature Geoscience.

Geological evidence has hinted that life existed in the oceans as far back as 3.8 billion years ago. But signs of terrestrial life have been rarer — possibly because much of the planet might have been under water until 3 billion years ago. [In Images: The Oldest Fossils on Earth]

The idea that life made landfall this early in Earth's history has been around for decades, said Hugo Beraldi Campesi, a geobiologist at the National Autonomous University of Mexico, who was not involved in the new research. "The problem was always the lack of hard evidence — until now." The new discovery adds to the growing body of evidence that the continents have harbored life for a long time, he added.

The researchers, led by Martin Homann, a sedimentologist at the European Institute for Marine Studies, discovered the fossilized microbes on the side of a rocky cliff in the Barberton Makhonjwa Mountains of eastern South Africa, home to some of the world's oldest geological features. The fossils are part of a chunk of rock called the Moodies Group, which represents one of the world's oldest shorelines, Lalonde said.

The microbes are extremely well-preserved, he said, showing thick sheets that blanket pebbles, a sign that the critters lived on an ancient riverbed — a terrestrial environment — rather than a sandy beach. Ripple-like features suggest that water flowed in one direction in this area, further evidence that the microbes lived along a river or, perhaps, an alluvial fan. That's a geological feature formed when runoff flows outward in the shape of a fan.

"This is essentially Earth's oldest riverbed," Lalonde told Live Science. "And it's already containing life."

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Unlike other evidence of land-based life, such as fossilized structures built by bacteria, the newfound fossils are of the preserved microbes themselves. The layered fossils formed when a layer of sediment covered a sheet of microbes, only later to have another blanket of microbes grow on top. Over time, layers of microbes and sediment stacked on top of each other like primordial lasagna and became preserved. Because these are directly preserved microbes, the fossils even contain organic matter, such as carbon and nitrogen atoms that once were part of the organisms.

An analysis of the type of nitrogen atoms present in the fossils suggests that the ancient microbes thrived by consuming nitrate, or a nitrogen atom bonded to three oxygen atoms, Lalonde said. When these microbes lived, during the Archean eon (which lasted from 4 billion to 2.5 billion years ago), Earth's atmosphere wasn't filled with oxygen as it is now. But a nitrate-based metabolism is the most energy-efficient type of metabolism after an oxygen-based one — which is what humans, for example, use. Nitrate would've given the microbes plenty of energy, Lalonde said.

"Life may not have been so rough in the Archean if you're on land," Lalonde said.

Indeed, the study suggests that Earth's landscape may already have been teeming with life at the time.

Historical development of life
- The evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to the present. Earth formed about 4.5 billion years (Ga) ago and evidence suggests life emerged prior to 3.7 Ga.

That is a time not long after the planet's formation and hundreds of millions of years before what is currently accepted as evidence for the most ancient life yet found on Earth.

The researchers report their investigation in the journal Nature.

As with all such claims about ancient life, the study is contentious. But the team believes it can answer any doubts.

The scientists' putative microbes from Quebec are one-tenth the width of a human hair and contain significant quantities of haematite - a form of iron oxide or "rust".

Matthew Dodd, who analysed the structures at University College London, UK, claimed the discovery would shed new light on the origins of life.

"This discovery answers the biggest questions mankind has asked itself - which are: where do we come from and why we are here?

"It is very humbling to have the oldest known lifeforms in your hands and being able to look at them and analyse them," he told BBC News.

The fossil structures were encased in quartz layers in the so-called Nuvvuagittuq Supracrustal Belt (NSB).

The NSB is a chunk of ancient ocean floor. It contains some of the oldest volcanic and sedimentary rocks known to science.

The team looked at sections of rock that were likely laid down in a system of hydrothermal vents - fissures on the seabed from which heated, mineral-rich waters spew up from below.

Today, such vents are known to be important habitats for microbes. And Dr Dominic Papineau, also from UCL, who discovered the fossils in Quebec, thinks this kind of setting was very probably also the cradle for lifeforms between 3.77 and 4.28 billion years ago (the upper and lower age estimates for the NSB rocks).

He described how he felt when he realised the significance of the material on which he was working: "I thought to myself 'we've got it, we've got the oldest fossils on the planet'.

"It relates to our origins. For intelligent life to evolve to a level of consciousness, to a point where it traces back its history to understand its own origin - that's inspirational."

Any claim for the earliest life on Earth attracts scepticism. That is understandable. It is often hard to prove that certain structures could not also have been produced by non-biological processes.

In addition, analysis is complicated because the rocks in question have often undergone alteration.

The NSB, for example, has been squeezed and heated through geological time

At present, perhaps the oldest acknowledged evidence of life on the planet is found in 3.48-billion-year-old rocks in Western Australia.

This material is said to show remnants of stromatolites - mounds of sediment formed of mineral grains glued together by ancient bacteria.

An even older claim for stromatolite traces was made in August last year. The team behind that finding said their fossil evidence was 3.70 billion years old.

Nonetheless, the UCL researchers and their colleagues say they have worked extremely hard to demonstrate the greater antiquity for their structures.

Dr Papineau does concede though that the idea of metabolising micro-organisms using oxygen so soon after the Earth's formation will surprise many geologists.

"They would not consider that there were organisms breathing oxygen at this time. It brings back the production of oxygen on the Earth's surface, albeit by tiny amounts, to the beginning of the sedimentary record," he said.

Prof Nicola McLoughlin from Rhodes University, South Africa, was not connected with the research.

She commended the scholarship but felt the data presented by the UCL-led team fell short.

"The morphology of these argued iron-oxidising filaments from Northern Canada is not convincing," she told BBC News.

"In recent deposits we see spectacular twisted stalks, often arranged in layers, but in the highly metamorphosed rocks of the Nuvvuagittuq belt the filaments are much simpler in shape.

"The associated textural and geochemical evidence of graphite in carbonate rosettes and magnetite-haematite granules is careful work, but provides only suggestive evidence for microbial activity; it does not strengthen the case for the biogenicity of the filaments."

She also said the maximum age of the rocks had proven to be very controversial, and that the true age was more likely to be closer to the 3.77-billion-year age.

Part of the interest in ancient life is in the implication it has for organisms elsewhere in the Solar System.

"These (NTB) organisms come from a time when we believe Mars had liquid water on its surface and a similar atmosphere to Earth at that time," said Mr Dodd.

"So, if we have lifeforms originating and evolving on Earth at this time then we may very well have had life beginning on Mars."

If that is the case then, according to Dr Papineau, recent Nasa rover missions to the Martian surface may have been looking for signs of life in the wrong places.

They are represented by tiny filaments, knobs and tubes in Canadian rocks dated to be up to 4.28 billion years old.

That is a time not long after the planet's formation and hundreds of millions of years before what is currently accepted as evidence for the most ancient life yet found on Earth.

The researchers report their investigation in the journal Nature.

As with all such claims about ancient life, the study is contentious. But the team believes it can answer any doubts.

The scientists' putative microbes from Quebec are one-tenth the width of a human hair and contain significant quantities of haematite - a form of iron oxide or "rust".

Matthew Dodd, who analysed the structures at University College London, UK, claimed the discovery would shed new light on the origins of life.

The fossil structures were encased in quartz layers in the so-called Nuvvuagittuq Supracrustal Belt (NSB).

The NSB is a chunk of ancient ocean floor. It contains some of the oldest volcanic and sedimentary rocks known to science.

Artwork

The team looked at sections of rock that were likely laid down in a system of hydrothermal vents - fissures on the seabed from which heated, mineral-rich waters spew up from below.

Today, such vents are known to be important habitats for microbes. And Dr Dominic Papineau, also from UCL, who discovered the fossils in Quebec, thinks this kind of setting was very probably also the cradle for lifeforms between 3.77 and 4.28 billion years ago (the upper and lower age estimates for the NSB rocks).

Any claim for the earliest life on Earth attracts scepticism. That is understandable. It is often hard to prove that certain structures could not also have been produced by non-biological processes.

In addition, analysis is complicated because the rocks in question have often undergone alteration.

The NSB, for example, has been squeezed and heated through geological time

At present, perhaps the oldest acknowledged evidence of life on the planet is found in 3.48-billion-year-old rocks in Western Australia.

The fossils were discovered by Dominic Papineau in an area of Quebec that was deep under the sea billions of years ago

This material is said to show remnants of stromatolites - mounds of sediment formed of mineral grains glued together by ancient bacteria.

An even older claim for stromatolite traces was made in August last year. The team behind that finding said their fossil evidence was 3.70 billion years old.

Nonetheless, the UCL researchers and their colleagues say they have worked extremely hard to demonstrate the greater antiquity for their structures.

Dr Papineau does concede though that the idea of metabolising micro-organisms using oxygen so soon after the Earth's formation will surprise many geologists.

Since the first life appeared in the Earth’s oceans about 3.8-billion years ago, the pattern of life on our planet has become increasingly complex.

Life has developed from those simple organisms, exploding into more than 1.3-million documented species of living things on Earth today. Scientists estimate there are between 30-million and 100–million species on Earth, though only about 1.3–million of these have been documented.

The development of life on Earth as we know it has generally been gradual, although there have been periods of rapid change. The most prolific profusion of species has occurred during the last eighth of Earth’s history, known as the Phanerozoic Era, within the past 543-million years.

Among the Earth’s first organisms were cyanobacteria: tiny, single-celled creatures which formed a film over the surface of mud and trapped coats of it, making layered structures called stromatolites. Stromatolites emerged soon after the Earth cooled and the atmosphere and oceans formed. Although now nearly extinct, these microbial mats are still forming in some places, such as in the highly saline waters of Shark Bay, in Western Australia.

Fossil stromatolites have been discovered in a wide variety of environments, from thermal springs to lakes, the sea and even below ice-covered lakes in Antarctica. Scientists have found fossil traces of stromatolites which are about 3.5-billion years old – some of the world’s oldest – near Barberton in the Mpumalanga Province of South Africa. Stromatolite fossils of a similar age have also been found in north-western Australia and Greenland. Fossil stromatolites have also been found at Sterkfontein.

The stromatolite fossil record is almost the only evidence we have of life on Earth for the first s

even-eighths of the planet’s existence.

The last eighth of the Earth’s history saw an explosion of life.

About 600-million years ago, the first sponges, jellyfish and flat worms appeared in the oceans. The first arthropods – millipedes and centipedes, and later spiders and scorpions – moved onto land about 450-million years ago. Insects first evolved about 400-million years ago and reptiles about 330-million years ago. The first mammals appeared about 220-million years ago, and the first birds about 150-million years ago. The first flowering plants began to grow about 118-million years ago. The last dinosaurs were wiped out about 65-million years ago, and the first primates – our ancient ancestors – appeared about 55-million years ago.

Earth is home to more than 4000 species of mammal

At present, classified species include 4,000 different mammals, 9,000 birds and 750,000 types of insects.

But hundreds – possibly thousands – of species are becoming extinct every year. Some estimates put the number of species dying out at about 100 every day; even conservative records of extinctions run to more than 500 a year.

Scientists regard Africa as a remnant of the Earth’s past diversity. Its relatively sparse human populations until now have allowed people and a great range of other species to co-exist. But this is changing fast. The amazing biodiversity of life on Earth is now under serious threat.

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Life has developed from those simple organisms, exploding into more than 1.3-million documented species of living things on Earth today. Scientists estimate there are between 30-million and 100–million species on Earth, though only about 1.3–million of these have been documented.

The development of life on Earth as we know it has generally been gradual, although there have been periods of rapid change. The most prolific profusion of species has occurred during the last eighth of Earth’s history, known as the Phanerozoic Era, within the past 543-million years.

Among the Earth’s first organisms were cyanobacteria: tiny, single-celled creatures which formed a film over the surface of mud and trapped coats of it, making layered structures called stromatolites. Stromatolites emerged soon after the Earth cooled and the atmosphere and oceans formed. Although now nearly extinct, these microbial mats are still forming in some places, such as in the highly saline waters of Shark Bay, in Western Australia.

Fossil stromatolites have been discovered in a wide variety of environments, from thermal springs to lakes, the sea and even below ice-covered lakes in Antarctica. Scientists have found fossil traces of stromatolites which are about 3.5-billion years old – some of the world’s oldest – near Barberton in the Mpumalanga Province of South Africa. Stromatolite fossils of a similar age have also been found in north-western Australia and Greenland. Fossil stromatolites have also been found at Sterkfontein.

The stromatolite fossil record is almost the only evidence we have of life on Earth for the first s

even-eighths of the planet’s existence.

Diversity

The last eighth of the Earth’s history saw an explosion of life.

About 600-million years ago, the first sponges, jellyfish and flat worms appeared in the oceans. The first arthropods – millipedes and centipedes, and later spiders and scorpions – moved onto land about 450-million years ago. Insects first evolved about 400-million years ago and reptiles about 330-million years ago. The first mammals appeared about 220-million years ago, and the first birds about 150-million years ago. The first flowering plants began to grow about 118-million years ago. The last dinosaurs were wiped out about 65-million years ago, and the first primates – our ancient ancestors – appeared about 55-million years ago.

Elephant 84186 1920

Earth is home to more than 4000 species of mammal

At present, classified species include 4,000 different mammals, 9,000 birds and 750,000 types of insects.

But hundreds – possibly thousands – of species are becoming extinct every year. Some estimates put the number of species dying out at about 100 every day; even conservative records of extinctions run to more than 500 a year.

Scientists regard Africa as a remnant of the Earth’s past diversity. Its relatively sparse human populations until now have allowed people and a great range of other species to co-exist. But this is changing fast. The amazing biodiversity of life on Earth is now under serious threat.

Life on Earth began more than 3 billion years ago, evolving from the most basic of microbes into a dazzling array of complexity over time. But how did the first organisms on the only known home to life in the universe develop from the primordial soup?

One theory involved a "shocking" start. Another idea is utterly chilling. And one theory is out of this world!

Inside you'll learn just how mysterious this all is, as we reveal the different scientific theories on the origins of life on Earth.

It started with an electric spark

Lightning may have provided the spark needed for life to begin.

Electric sparks can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen, as was shown in the famous Miller-Urey experiment reported in 1953, suggesting that lightning might have helped create the key building blocks of life on Earth in its early days. Over millions of years, larger and more complex molecules could form. Although research since then has revealed the early atmosphere of Earth was actually hydrogen-poor, scientists have suggested that volcanic clouds in the early atmosphere might have held methane, ammonia and hydrogen and been filled with lightning as well.

Molecules of life met on clay

The first molecules of life might have met on clay, according to an idea elaborated by organic chemist Alexander Graham Cairns-Smith at the University of Glasgow in Scotland. These surfaces might not only have concentrated these organic compounds together, but also helped organize them into patterns much like our genes do now.

The main role of DNA is to store information on how other molecules should be arranged. Genetic sequences in DNA are essentially instructions on how amino acids should be arranged in proteins. Cairns-Smith suggests that mineral crystals in clay could have arranged organic molecules into organized patterns. After a while, organic molecules took over this job and organized themselves.

Life began at deep-sea vents

The deep-sea vent theory suggests that life may have begun at submarine hydrothermal vents spewing key hydrogen-rich molecules. Their rocky nooks could then have concentrated these molecules together and provided mineral catalysts for critical reactions. Even now, these vents, rich in chemical and thermal energy, sustain vibrant ecosystems.

Life had a chilly start

Ice might have covered the oceans 3 billion years ago, as the sun was about a third less luminous than it is now, scientists say. This layer of ice, possibly hundreds of feet thick, might have protected fragile organic compounds in the water below from ultraviolet light and destruction from cosmic impacts. The cold might have also helped these molecules to survive longer, allowing key reactions to happen.

The answer lies in understanding DNA formation

Nowadays DNA needs proteins in order to form, and proteins require DNA to form, so how could these have formed without each other? The answer may be RNA, which can store information like DNA, serve as an enzyme like proteins, and help create both DNA and proteins. Later DNA and proteins succeeded this "RNA world," because they are more efficient.

RNA still exists and performs several functions in organisms, including acting as an on-off switch for some genes. The question still remains how RNA got here in the first place. And while some scientists think the molecule could have spontaneously arisen on Earth, others say that was very unlikely to have happened. Other nucleic acids other than RNA have been suggested as well, such as the more esoteric PNA or TNA.

Life had simple beginnings

Instead of developing from complex molecules such as RNA, life might have begun with smaller molecules interacting with each other in cycles of reactions. These might have been contained in simple capsules akin to cell membranes, and over time more complex molecules that performed these reactions better than the smaller ones could have evolved, scenarios dubbed "metabolism-first" models, as opposed to the "gene-first" model of the "RNA world" hypothesis.

Life was brought here from elsewhere in space

Perhaps life did not begin on Earth at all, but was brought here from elsewhere in space, a notion known as panspermia. For instance, rocks regularly get blasted off Mars by cosmic impacts, and a number of Martian meteorites have been found on Earth that some researchers have controversially suggested brought microbes over here, potentially making us all Martians originally. Other scientists have even suggested that life might have hitchhiked on comets from other star systems. However, even if this concept were true, the question of how life began on Earth would then only change to how life began elsewhere in space.

Evidences of life

Fossil evidence informs most studies of the origin of life. The age of the Earth is about 4.54 billion years; the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago.

Scientists have discovered what they say could be fossils of some of the earliest living organisms on Earth.

They are represented by tiny filaments, knobs and tubes in Canadian rocks dated to be up to 4.28 billion years old.

That is a time not long after the planet's formation and hundreds of millions of years before what is currently accepted as evidence for the most ancient life yet found on Earth.

The scientists' putative microbes from Quebec are one-tenth the width of a human hair and contain significant quantities of haematite - a form of iron oxide or "rust".

https://ichef.bbci.co.uk/news/304/cpsprodpb/44BF/production/_94899571_history_of_earth3.png

Historical Development of life

Radioactive Decay studies of rocks

Based on this it was revealed that Earth is around 4.5 billion years old- 1 billion years older than the oldest fossils

Extra Terrestrial Origin

Hypothesis explains that life originated from another planet outside the Solar System

Panspermia

This theory presumes that the "seed" of life exists all over the universe and can be propagated through the space, and that life on Earth originated from those seeds.

Divine Creation

Theory where many people believed that life was put on early Earth by divine forces. Creation theories are common to many of the world's religions and cultures.

Origin from Non-Living Matter

Belief that life arose on Earth from inanimate matter after Earth had cooled. Random events produced stable molecules that could self-replicate. Natural selection favored changes in the rate or reproduction which eventually led to the first cell.

Stanley Miller and Harold Urey

Performed an experiment that replicated the early Earth conditions and provided proof of amino acids and other molecules could be formed.

Hydrogen, Carbon Dioxide, Methane, Water Vapor, Nitrogen, Ammonia and Carbon Monoxide

Simple molecules that were probably present in the early Earth's atmosphere

Amino Acids

The building blocks of proteins

Cell Membrane

Seperates the cell from its environment which contains lipids

Coacervates

When lipids mix with water they form bubbles that are called?

Prokaryotes

Scientists believed that the first cells were the?

Prokaryotes

Organisms whose cells have no nucleus

Anaerobic

The first prokaryotes

Anaerobic

They do not need and could not tolerate oxygen

4.5 Billion Years Old

Estimated age of the Earth

Eubacteria

(True bacteria) Most living bacteria including those that causes diseases and decomposition

Archaebacteria

(Ancient bacteria) rare and are found mainly in hostile environments where conditions resemble those of early Earth (salty lakes, hot springs, swamps, ocean floors)

Eukaryotes

More complex life formed-appeared in the fossil record which are known as?

Plants and fungi

The first living things to populate the surface of the land

Arthropods

Animals with hard covering and jointed legs and the first animals to live on water

0.5 BYA

Rapid diversification of animals, plants and fungi appear, origin of the humans (about 2 million years ago)

1.0 BYA

Earliest animals; first multicellular organisms; diverse protists

1.5 BYA

First prokaryotes

2.0 BYA

Diverse and abundant bacteria

2.5 BYA

Photosynthesis begins

3.0 BYA

Bacteria diversity

3.5 BYA

First bacteria appeared

4.0 BYA or 3.8 billion years ago

Oldest Rocks

4.5 BYA

Earth forms

That is a time not long after the planet's formation and hundreds of millions of years before what is currently accepted as evidence for the most ancient life yet found on Earth.

Life has developed from those simple organisms, exploding into more than 1.3-million documented species of living things on Earth today. Scientists estimate there are between 30-million and 100–million species on Earth, though only about 1.3–million of these have been documented.

The development of life on Earth as we know it has generally been gradual, although there have been periods of rapid change. The most prolific profusion of species has occurred during the last eighth of Earth’s history, known as the Phanerozoic Era, within the past 543-million years.

Among the Earth’s first organisms were cyanobacteria: tiny, single-celled creatures which formed a film over the surface of mud and trapped coats of it, making layered structures called stromatolites. Stromatolites emerged soon after the Earth cooled and the atmosphere and oceans formed. Although now nearly extinct, these microbial mats are still forming in some places, such as in the highly saline waters of Shark Bay, in Western Australia.

Fossil stromatolites have been discovered in a wide variety of environments, from thermal springs to lakes, the sea and even below ice-covered lakes in Antarctica. Scientists have found fossil traces of stromatolites which are about 3.5-billion years old – some of the world’s oldest – near Barberton in the Mpumalanga Province of South Africa. Stromatolite fossils of a similar age have also been found in north-western Australia and Greenland. Fossil stromatolites have also been found at Sterkfontein.

The stromatolite fossil record is almost the only evidence we have of life on Earth for the first s

even-eighths of the planet’s existence.



7 THEORIES ON ORIGIN OF LIFE 

1. he started with an electric spark
2.moleciles of-life met on clay
3.life began at deep sea vents
4.life had a chilly start

It is generally agreed that all life today evolved by common descent from a single primitive lifeform.[2] It is not known how this early form came about, but scientists think it was a natural process which took place perhaps 3,900 million years ago. This is in accord with the philosophy of naturalism: only natural causes are admitted.

It is not known whether metabolism or genetics came first. The main hypothesis which supports genetics first is the RNA world hypothesis, and the one which supports metabolism first is the protein world hypothesis.

Another big problem is how cells develop. All existing forms of life are built out of cells.[3]

Melvin Calvin, recipient of the Nobel Prize in Chemistry, wrote a book on the subject,[4] and so did Alexander Oparin.[5] What links most of the early work on the origin of life is the idea that before life began there must have been a process of chemical change.[6] Another question which has been discussed by J.D. Bernal and others is the origin of the cell membrane. By concentrating the chemicals in one place, the cell membrane performs a vital function.[7]

Many religions teach that life did not evolve spontaneously, but was deliberately created by a god. Such theories are a part of creationism, which has "old earth" and "young earth" versions. Because of lack of evidence for such views, almost all scientists do not accept them