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1. For how long has there been life on Earth?  2. For what percentage of time has life existed on Earth (round to the nearest whole number). 3. For about how many years of geological time have humans existed on Earth? 4. For about how many years of geological time have the dinosaurs existed on Earth?  5. Did dinosaurs exist at the same time as humans?  6. How do scientists determine when an era begins and when it ends? 7. What is the purpose of making a geological timeline? 

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1. For how long has there been life on Earth?  2. For what percentage of time has life existed on Earth (round to the nearest whole number). 3. For about how many years of geological time have humans existed on Earth? 4. For about how many years of geological time have the dinosaurs existed on Earth?  5. Did dinosaurs exist at the same time as humans?  6. How do scientists determine when an era begins and when it ends? 7. What is the purpose of making a geological timeline? 

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Firts Jawed Fish

400 million years ago.

The first record of the jawed Placodermi is from the Early Devonian, about 400 million years ago. The placoderms flourished for about 60 million years and were almost gone at the end of the Devonian. Nothing is known of their ancestors, who must have existed in the Silurian.

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Start of the age of the dinosaurs

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The Mesozoic era saw the rise of some of the most iconic animals, from Tyrannosaurus rex to birds and mammals.

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first mammals:

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American History Part 1.1- The Cenozoic Era

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Earthworms

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https://youtu.be/2kGHLOuzy88

Homo sapiens, (Latin: “wise man”) the species to which all modern human beings belong. Homo sapiens is one of several species grouped into the genus Homo, but it is the only one that is not extinct. See also human evolution.

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FIRST PEOPLES | Homo sapiens -The Curious Species | PBS

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First flowering plants

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Dinosaurs extinction.

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WION Gravitas: World's first cloned primates

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First Charks

The earliest shark-like teeth we have come from an Early Devonian (410-million-year-old) fossil belonging to an ancient fish called Doliodus problematicus. Described as the 'least shark-like shark', it is thought to have risen from within a group of fish known as acanthodians or spiny sharks.

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Grasses

Poaceae or Gramineae is a large and nearly ubiquitous family of monocotyledonous flowering plants known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and pasture.

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Precambrian, period of time extending from about 4.600 billion years ago (the point at which Earth began to form) to the beginning of the Cambrian period, 541 million years ago.The Precambrian represents more than 80 percent of the total geologic record.

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The cyanobacteria and archae of primitive Earth are also referred to as prokaryotes (together with the eubacteria). Prokaryotes are discussed in Chapter 16. Approximately 1.5 billion years ago, in an oxygen-containing atmosphere, the first eukaryotes came into being.

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Julia G.

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Eons of the Precambrian

The primary way we get an understanding of Earth's history is by studying the rocks and fossils leftover from various time periods. The difficulty in studying the Precambrian period is that many of the rocks from that time have eroded away or metamorphosed so they are not recognizable in their original form.

The beginning of the Precambrian period starts with the formation of Earth about 4.5 billion years ago and ends at the first sign of complex life about 540 million years ago. Though the Precambrian Period is often referred to as a period, it's actually the only supereon, which means that it spans multiple eons. The Precambrian has been divided into three eons: the Hadean, the Archean, and the Proterozoic.

Hadean

The Hadean eon took place 4,500 - 4,000 million years ago. As our planet formed, gravity pulled gas and dust from the solar system into what we know now as Earth. Friction then heated the material that would eventually become Earth into a sphere of hot molten lava. At this time the earth was a very harsh environment; there was no solid crust, just molten lava covering the surface. All the water that we see in the oceans, lakes, rivers, and glaciers were evaporated in the atmosphere. Just imagine the humidity!

If this wasn't enough, asteroid impacts were a common occurrence on the young planet. Some scientists believe the moon was formed by one such collision. It is theorized that a Mars-sized object crashed into Earth early in the Hadean eon. The theory states that the impact caused a large amount of debris to be ejected from Earth, which later combined to form the moon.

Archean

The Archean eon took place 4,000 - 2,500 million years ago. Over time, as the earth cooled, the outer edge of the planet solidified from molten lava to a solid crust. Although it wasn't perfectly solid, large volcanoes were erupting all over Earth and forming new land. With the crust shifting and cracking below, collisions formed the beginnings of early continents.

As the earth cooled even more, the water in the atmosphere began to rain out. All the water that was evaporated in the atmosphere began to pour down onto the newly formed solid ground. By this eon in the Precambrian, most of the water had rained down from the atmosphere and covered Earth with a global ocean.

It is believed that the first signs of life formed during the Archean eon in these oceans. Carbon dating from fossils found in Western Australia show evidence that a small single-cell organism named cyanobacteria, or more commonly known as blue-green algae, was present in the ocean around 3,000 million years ago.

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the precambrian period: events & facts - video & lesson transcript | study.com

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The Precambrian Period: Events & Facts - Video & Lesson Transcript | Study.com

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The primary way we get an understanding of Earth's history is by studying the rocks and fossils leftover from various time periods. The difficulty in studying the Precambrian period is that many of the rocks from that time have eroded away or metamorphosed so they are not recognizable in their original form.

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A prokaryote is a cellular organism that lacks an envelope-enclosed nucleus.
But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains.