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Today's Wonder of the Day was inspired by Ms. Noble's Grade 3 Class from Barrie. Ms. Noble's Grade 3 Class Wonders, " How are rocks made " Thanks for WONDERing with us, Ms. Noble's Grade 3 Class!

Do you like to know how things are made? For example, when you order a grilled cheese sandwich, do you like to know what kind of bread and cheese are going to be used? If you don't want a Swiss cheese on rye sandwich, then you probably have an interest in how your sandwich is constructed.

But what about the bread and the cheese? Are you curious about how those products are made? Sometimes it's easy to see how things come to be the way they are. For bread, it's easy to follow a recipe that shows how ground grains are combined with other ingredients to produce the bread that comes hot and fresh out of the oven.

For other things, though, it's not nearly as easy to figure out how they're made. Take rocks, for example. Can you look at a and determine how it came to be? Unless you're a , the answer is probably "no." So how are those hard lumps of matter made?

That's a bit of a trick question, though, because there are three main types of rocks: igneous, sedimentary, and metamorphic. And, of course, each type forms differently. Let's take a look at each type of and how it comes to be.

Igneous rocks when melted cools into a . This can happen underground, where liquid is found in the of , or above the ground, where is released during a volcanic eruption. Common examples of igneous rocks include granite, basalt, pumice, and obsidian.

While igneous rocks can in a matter of minutes as erupts and cools quickly on Earth's surface, sedimentary rocks can take millions of years to . When and surface materials over time, they leave layers of sediments.

Over long periods of time, upon of sediments , putting intense on the oldest layers. Under great and , lower layers of sediments eventually turn into rocks. Common examples of sedimentary rocks include sandstone, limestone, and shale.

Metamorphic rocks are the products of rocks that have undergone changes. If you're familiar with the term as it describes the change a caterpillar goes through to become a butterfly, then you'll understand that the term also applies to rocks that change in .

Metamorphic rocks may have started out as igneous, sedimentary, or even another type of metamorphic . Changes in these rocks are spurred either by collisions that occur at the boundaries of colliding tectonic plates or intense and underground. Common types of metamorphic rocks include marble, soapstone, slate, and gneiss.

Although they might seem rather , rocks actually change over the course of millions of years as part of what scientists call the . For example, a volcano erupts, spewing that turns into igneous .

Over time, weather erodes that igneous , turning it into small pieces of . In turn, those pieces of become layers of compacted that turn into sedimentary over the course of millions of years.

Over millions of more years, that sedimentary gets buried under other rocks and ends up deep underground. and deep in the Earth's crust turn the sedimentary into metamorphic , and the can start all over again! Of course, rocks don't have to follow this exact progression. There's a nearly endless variety of ways rocks can turn from one type into another in a never-ending .

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Today's Wonder of the Day was inspired by Ms. Noble's Grade 3 Class from Barrie. Ms. Noble's Grade 3 Class Wonders, " How are rocks made " Thanks for WONDERing with us, Ms. Noble's Grade 3 Class! Do you like to know how things are made?

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Have you ever collected rocks? To some kids, collecting rocks might not seem all that interesting. But others know that it can be really cool to upon a uniquely colored or shaped rock when you're at the park, at the beach, or simply at home. Where did it come from? And how long has it been around?

When you think of things that are and last forever, rocks probably come to mind. Whether it's a mountain, a stone courthouse, or a gravestone in a local cemetery, rocks do seem to have staying power.

In fact, rocks might even seem indestructible . If you look closely at old rocks, though, you'll see signs of wear. Although rocks are indeed materials, they're still not from the physical and chemical forces of nature that inevitably wear away at everything on Earth.

Scientists call the process that rocks weathering. Weathering occurs in two main forms: mechanical and chemical. Mechanical weathering processes break rocks down into smaller pieces but do not change their chemical composition .

Chemical weathering processes, on the other hand, break down rocks chemically , changing them into different types of rocks and minerals. Some of those new materials can be dissolved by exposure to water and air, leading to erosion.

Mechanical and chemical weathering processes can simultaneously , but they're still extremely slow processes. Since it takes so long to break down and rocks, we see them as a lasting, nearly- indestructible material.

Let's take a look at a chemical weathering process that you're already somewhat with...even if you don't realize it. When rain falls from the sky, some of the water mixes with carbon dioxide in the air or pockets of air in the . This mixture forms a weak acid called carbonic acid.

As carbonic acid down through the and comes into contact with cracks in the rock underground, it can react chemically with the rock, causing it to . Carbonic acid is particularly reactive with calcite, which is the primary mineral in limestone.

Over long periods of time, carbonic acid dissolves limestone, creating pits and holes and enlarging cracks and openings in the rock. This creates a unique type of topography known as karst topography . Common features of karst topography you're probably with include caves, caverns, sinkholes, and springs.

Another common type of chemical weathering occurs as a result of acid rain. Acid rain forms when rain combines with nitrogen and sulfur to create nitric and sulfuric acids, which can calcium-based rocks such as marble and limestone. Acid rain tends to be a problem in areas with higher levels of pollution from coal-burning power plants.

Although weathering of rock might seem like a negative thing, it's actually a natural process that eventually creates valuable products. Weathered rock is the primary of . Minerals from weathered rock sustain all sorts of plant life through the . We also wouldn't be able to visit super-cool caves without the chemical weathering of rock!

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Have you ever collected rocks? To some kids, collecting rocks might not seem all that interesting. But others know that it can be really cool to upon a uniquely colored or shaped rock when you're at the park, at the beach, or simply at home. Where did it come from?

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Do you love rocks? Most children enjoy finding and playing with interesting rocks. They can be found in all sorts of shapes and sizes. More importantly, they can also be found in a wide variety of beautiful colors. But exactly how do rocks get their colors?

Here on Earth, we live on a rocky planet. The continents themselves are massive slabs of stone. Mountain ranges jut into the sky all around the world. Even the sea floor consists of rocky bottoms.

Earth is just one of four rocky planets in our solar system. The others are Mercury, Venus, and Mars. The remaining planets - Jupiter, Saturn, Uranus, and Neptune - are made mostly of gas. Many of Earth's rocks are covered by grasses, forests, and bodies of water. On other planets and Earth's Moon, is all you see.

Earth's many rocks can take on a - of colors. From bright reds and oranges to browns and grays, Earth's rocks can a beautiful picture in nature.

All those colors are the result of the minerals that make up the rocks. Minerals are the building blocks of . Some rocks consist of just one type of , but most rocks contain a few different types of minerals joined together.

Scientists there are as many as 4,000 different types of minerals. Each has its own chemical composition , which helps to determine what it will be. A 's can also be affected by chemical impurities , interaction with other minerals, and environmental factors.

Like all objects, a 's depends upon which wavelengths of light it absorbs and reflects. The bonds within a generally determine which wavelengths of light will be absorbed and which will be reflected. Those wavelengths that are reflected back to our eyes determine the of the .

Some minerals have free electrons that will absorb certain wavelengths of light. Upon absorption , that extra energy may be emitted as another wavelength of light to get rid of the extra energy. If that combines with impurities or other minerals, its structure can change, thereby affecting what wavelengths of light are reflected and possibly changing its .

Minerals can take on different colors depending upon their internal structure. For example, the in your pencil and diamonds are both pure carbon. Differences in how they formed, however, gave them different structures, and thus very different colors and properties.

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We believe you'll think today's colorful Wonder of the Day totally rocks!

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Today's Wonder of the Day was inspired by Miah. Miah Wonders, " How are geodes made? " Thanks for WONDERing with us, Miah!

If you're ever hiking in the deserts of Arizona or the stream beds of Iowa or the forests of Indiana, you might run across some unique rocks. Mostly round and varying in size from a tennis ball to a softball, these interesting stones aren't quite as heavy as you expect them to be.

In fact, they seem almost inside. Resting on a nearby log, you decide to pound the against a large flat to see what happens. It splits open and you're amazed to find colorful crystals inside. What have you discovered? A geode, of course!

Geodes are spherical rocks that contain cavities lined with crystals. The name geode comes from the Greek word Geoides, which means "earthlike." These unique rocks can be formed in a variety of ways.

In volcanic , geodes start out as bubbles. Geodes can form in areas far away from volcanoes, too. In sedimentary , geodes might start out as animal burrows, deposits, or even roots.

Over time, the air, , or roots create a within the , while the outer edges harden into a spherical shape. Then the real scientific magic happens as groundwater begins to around and through these rocks.

Groundwater naturally picks up a variety of minerals as it makes its way down from the surface. These minerals, including quartz, , and calcite among others, become dissolved in the groundwater and then get deposited on the inside of developing geodes over long periods of time.

After thousands of years of groundwater , what is the result? You can see the beautiful result when you open a geode to reveal points and/or layers of banded crystals inside the geode's .

Like a fingerprint, every geode is unique, because each geode has a unique composition that is different from every other geode. The only way to discover the beauty inside of a geode is to crack it open with a hammer or cut it open with a .

Geodes will vary widely in terms of their size, formation, and colors. Some of the most prized geodes are those that feature rare black calcite or crystals.

Geodes can be found all over the world. Areas with the most geodes, however, tend to be deserts, volcanic ash beds, or areas with plentiful . In the United States, for example, you can find plenty of geodes in California, Arizona, New Mexico, Utah, Nevada, Iowa, Missouri, Illinois, Indiana, Kentucky, and Ohio.

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Today's Wonder of the Day was inspired by Miah. Miah Wonders, " How are geodes made? " Thanks for WONDERing with us, Miah! If you're ever hiking in the deserts of Arizona or the stream beds of Iowa or the forests of Indiana, you might run across some unique rocks.

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You might know that diamonds, gold, and other jewels are rare, which makes them valuable. But have your ever wondered where diamonds come from - how they are actually made?

Thousands, millions and maybe even billions of years ago, extreme heat and pressure turned pure into colorless crystals 100 miles or more below the Earth's surface. Diamonds are the only made of only one : .

Eventually, activity brought diamonds closer to the Earth's surface. pipes - known as kimberlite pipes - push diamonds to the surface, cooling them along the way. Today, diamonds are mined in areas that have experienced activity in the past, as well as in gravel beds and ocean floors.

Diamonds were first discovered and mined in India over 2,400 years ago. Over time, diamonds were found in many other areas around the world, including many in Africa. In today's trade, Africa, Russia, Australia, and Canada produce the most diamonds.

As diamonds travel to the surface of the Earth, they occasionally mix with amounts of other minerals and take on a variety of colors. Completely colorless diamonds are very rare and expensive. Most diamonds have a bit of brown or yellow in them. Other rarer colors include blue, red, orange, pink, and green.

While these beautiful and popular gemstones may look like delicate glass, they are actually the hardest natural substance on Earth. While it's possible for diamonds to shatter or burn under extreme conditions, only a can scratch or cut another . In fact, diamonds take their name from the Greek word for " indestructible ."

Diamonds' tough natural properties make them popular in industrial settings, where they are used in all sorts of , such as drills and saws. Experts estimate that up to 80% of all diamonds are used for industrial purposes. Only about 20% of diamonds are gem quality and used for jewelry.

Since the 1950s, diamonds have also been produced by man. Duplicating the natural processes that occur deep below the surface of the Earth in laboratories, manufacturers learned to create their own diamonds for industrial uses.

Recently, however, some manufacturers have been able to produce gem-quality diamonds in the laboratory. "Grown" by man in a matter of days rather than millions of years, these man-made diamonds have the same chemical, physical and optical qualities of mined natural diamonds.

With differences invisible to the naked eye, special testing in a laboratory is often necessary to distinguish man-made diamonds from mined natural diamonds. While beautifully-colored stones are relatively rare in nature, man-made diamonds can be uniquely colored during the manufacturing process. Compared to natural stones, man-made diamonds are usually less expensive.

In case you're wondering why "diamonds are a girl's best friend," it probably has to do with the fact that diamonds are the most popular in the world. That popular saying came from the title of a song of the same name, first introduced in the original Broadway production of Gentlemen Prefer Blondes. Marilyn Monroe's version of the song from the film version of the Broadway show was named the 12th most important movie song of all time by the American Film Institute.

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You might know that diamonds, gold, and other jewels are rare, which makes them valuable. But have your ever wondered where diamonds come from - how they are actually made? Thousands, millions and maybe even billions of years ago, extreme heat and pressure turned pure into colorless crystals 100 miles or more below the Earth's surface.

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Do dinosaurs you? We love dinosaurs here in Wonderopolis! Wouldn't it have been cool to live in the time of the dinosaurs?

What do you think was like back then? Can you imagine having a picnic under a large tree while a pterodactyl flies overhead? Or playing a game of soccer with your friends while a tyrannosaurus runs across the field in pursuit of a stegosaurus ?

What do you think the dinosaurs looked like? Do you ever WONDER what they sounded like? How about how their skin felt? Did they play? Were they friendly? How big were they? Why did they become ?

If these questions interest you, you might have a future in paleontology. Paleontologists are scientists who study the history of on Earth. In particular, paleontologists often focus on organisms that lived long, long ago.

Paleontologists are often linked closely to dinosaurs, which makes sense since paleontologists are the scientists who have been able to tell us so much about the dinosaurs as a result of their studies. However, paleontology is much broader than just studying dinosaurs.

Most paleontologists study all sorts of forms, including plants and even single-cell organisms. Much of their work centers on finding the fossilized remains of these various forms of .

A paleontologist 's career involves field work, such as digging for fossils, as well as research, laboratory experiments, and writing about the findings. You may have seen pictures or museum exhibits about paleontologists on a "" out in the field.

Paleontologists investigate sites all over the world. In fact, you might find paleontologists practically anywhere that fossilized remains might be found. Paleontologists work hard to find fossils and retrieve them. They then usually take them back to a laboratory to clean, study and preserve them.

Paleontologists don't always know what they've found until they get their samples back to the lab. What they thought was a new species might end up being a piece of a fossil that has already been identified. Of course, the most exciting discoveries are those fossils from species that no one has ever seen before.

When paleontologists find fossils from new species, they must do research to make educated guesses about what the plant or animal might have looked like. Many of the images of dinosaurs we have come from paleontologists who have made guesses about what certain dinosaurs must have looked like.

Sometimes these images change over time as paleontologists find more specimens. For example, finding more bones from a particular might change a paleontologist 's mind about what the animal must have looked like.

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Do dinosaurs you? We love dinosaurs here in Wonderopolis! Wouldn't it have been cool to live in the time of the dinosaurs? What do you think was like back then? Can you imagine having a picnic under a large tree while a pterodactyl flies overhead?

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Have you ever WONDERed how scientists can know so much about things that happened thousands of years ago? For example, how do they know what certain dinosaurs looked like? After all, those dinosaurs have been for thousands of years, right?

But what about the parts of those dinosaurs that were left behind? Occasionally, bones, teeth, and other parts may have left an in a that survives to this day. When scientists find these imprints - like an x-ray - they can learn a lot about the animals that left them. What are we talking about? Fossils, of course!

Fossils are the actual remains or impressions left by plants or animals that were once alive hundreds or thousands of years ago. Over time, the (living) material left behind is replaced with minerals, leaving a that is like stone but looks like the original or .

Not all and remains become fossilized over time. Certain conditions have to exist for fossilization to take place. For example, many fossils form when and remains are buried - and thereby preserved - by mud, sand, or soil.

Fossilization also takes a lot of time. How long? How about 10,000 years or more. So if you go and bury a leaf under a pile of mud in the backyard, don't expect a to form in your lifetime!

Despite the requirements of time and preservation , fossils can be found just about anywhere. From the tops of mountains to the depths of the seas, fossils can be found all over Earth. Some sit on top of sandy beaches while others stay hidden deep underground.

Fossils are often unearthed during construction or new mining projects. As the ground is dug up and moved about, fossils once hidden deep underground suddenly come to light. In a similar way, you can often find fossils in shallow stream beds, as the constantly flowing water cuts through old earth to what's hidden below.

From time to time, you might hear the term "living ." Knowing what you already know about fossils, this probably seems like an odd term. However, it's used to refer to alive today that are the exact same as for which fossils have been found. This means that these have been alive for tens of thousands or even millions of years and remain unchanged.

One example is the non-flowering called Ginkgo, of which there is one considered a living : Ginkgo biloba. Scientists have found fossils recognizable as relatives of modern Ginkgo biloba from 270 million years ago!

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Have you ever WONDERed how scientists can know so much about things that happened thousands of years ago? For example, how do they know what certain dinosaurs looked like? After all, those dinosaurs have been for thousands of years, right? But what about the parts of those dinosaurs that were left behind?

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Today's Wonder of the Day was inspired by Charlotte from Chagrin Falls, OH. Charlotte Wonders, " Who discovered the first dinosaur bone? " Thanks for WONDERing with us, Charlotte!

Are you afraid of snakes? What about lizards and other reptiles? It's understandable to be around such creatures if you them in the . But what if you had bigger and fiercer creatures to worry about?

Could you imagine hiking in the during the time of the dinosaurs? Instead of a snake or a lizard, you'd have to watch out for huge beasts with long teeth and sharp claws. Some of them could even fly!

Thanks to modern science, we know a lot about the dinosaurs that used to Earth. How do scientists know so much? It's not like they can them in the like they do with modern animals. Instead, they rely upon what dinosaurs left behind. No, not their diaries! Scientists study their fossilized bones and, sometimes, other bodily material .

No one knows when the first dinosaur bone was found. Ancient peoples most likely uncovered fossils of dinosaur bones from time to time, but they had no idea what they had found. Ancient Chinese writings from over 2,000 years ago reference "" bones, which many experts today believe had to be dinosaur fossils.

Even early scientists weren't sure about the fossils they found. For example, in 1676, Reverend Robert Plot, a of an English , discovered a large thigh bone in England. He believed it belonged to ancient species of human "giants."

Although the disappeared eventually , drawings of it remain. Based upon those drawings, modern scientists believe it was probably from a dinosaur known as "Megalosaurus."

Megalosaurus is believed to be the first dinosaur ever described scientifically. British fossil hunter William Buckland found some fossils in 1819, and he eventually described them and named them in 1824. Like scientists before him, Buckland thought the fossils belonged to an ancient, larger version of a modern reptile.

As of that time, the word "dinosaur" still had not been invented yet, and dinosaurs hadn't yet been recognized as creatures that were significantly different than modern reptiles. All that changed when British scientist Richard Owen came along.

In late 1841 or early 1842, Owen viewed the fossil collection of William Devonshire Saull. He was by a fossilized chunk of spine, which was thought to belong to an ancient reptile similar to an iguana that had been called "Iguanodon."

Owen began comparing the fossils he saw and, within a few months, came to two critical conclusions: (1) that the fossils were from similar creatures; and (2) these were creatures unlike anything on Earth today. He coined the term "dinosaurs," which means "terrible lizards."

Although the study of dinosaurs really got its start in 1842, new evidence to study was hard to come by until the late 1800s. At that time, Othniel Marsh and Edward Cope, two American scientists who were both wealthy and competitive, formed research teams and headed for the Rocky Mountains.

Their competing teams unearthed tons of bones from several different sites. Known as the Bone Wars, their rivalry was responsible for the discovery of 136 new species of dinosaurs. As the 1900s began, many scientists and prestigious institutions all over the world were inspired by the Bone Wars to study dinosaurs.

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Today's Wonder of the Day was inspired by Charlotte from Chagrin Falls, OH. Charlotte Wonders, " Who discovered the first dinosaur bone? " Thanks for WONDERing with us, Charlotte! Are you afraid of snakes? What about lizards and other reptiles? It's understandable to be around such creatures if you them in the .

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Did you realize you can take a trip back in time to the Ice Age in the heart of one of America's largest modern cities? It's true! What are we talking about? The La Brea Pits in Los Angeles, California, of course!

The heart of Los Angeles is the site of a fascinating scientific . Within Hancock Park lie the La Brea Pits. The pits are areas where - brea in Spanish - has up from under the ground for 40,000 years or more.

The in the pits consists of heavy oil called . Oil fields underlie much of the ground in the area, and oil seeps to the surface and collects in pools at several different areas.

Big pools of oil don't sound all that exciting. So what's so special about the La Brea Pits? It's actually what can be found within the pits that has amazed scientists for many years.

The in the pits gets very thick. Sometimes it doesn't even look like , because it gets covered with dust, leaves and water. Over the years, many animals have been fooled into thinking they're on solid ground when, in reality, they end up getting stuck in .

Over hundreds and thousands of years, animals trapped in the have died and sunk into the . The does a fabulous job of preserving the bones of these animals. The also preserves all sorts of other fossils, including plants, insects and seeds.

The pits were initially used as a source of asphalt by early settlers in the area. Eventually, bones were found and scientists began to search the area for fossilized evidence of the area's history.

Since the early 1900s, scientists have excavated over 100 pits to search for the bones of large mammals that lived long, long ago. The oldest fossils found have been dated to about 38,000 years ago.

So what animals roamed the Los Angeles area tens of thousands of years ago? Several different species have become associated with the La Brea Pits because of fossilized remains found at the site, including -toothed cats, mammoths, wolves, bears, ground sloths, and horses.

The fossils that have been found in the pits can be seen at the George C. Page Museum in Hancock Park. Because of the valuable fossils recovered so far, the La Brea Pits were named a registered National Natural Landmark.

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Did you realize you can take a trip back in time to the Ice Age in the heart of one of America's largest modern cities? It's true! What are we talking about? The La Brea Pits in Los Angeles, California, of course! The heart of Los Angeles is the site of a fascinating scientific .

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The word "petrified" comes from the Greek word petro, which means "rock" or "." Around Halloween, you may hear people say they're petrified.

They mean they're very scared of something - scared enough that they've turned to and cannot move! If you ever find yourself petrified, you may be standing as still as a in a petrified forest.

Petrified is what scientists call the fossilized remains of trees that have turned into through a process called "permineralization." This process occurred underground when, millions of years ago, became buried under (like ).

initially preserves the by insulating it from oxygen, which usually starts the decomposition process. Over time, all the (living) materials in the slowly and are replaced with minerals. These minerals are usually silicates (like ).

Water with these minerals flows through the . As it does so, it deposits minerals in the 's cells. The 's plant cells , and a forms in their place.

Petrified is different than other types of fossils. Most fossils are impressions or compressions. Petrified , on the other hand, is a three-dimensional fossil that retains the original structure of the .

Petrified gives scientists great insight into plants from millions of years ago. In fact, minute details, like rings, can often be seen in great detail.

Scientists believe that can become petrified in less than 100 years. Areas with large amounts of petrified become known as petrified forests.

Many examples of petrified contain a wide variety of bold, beautiful colors. Although pure crystals are colorless, other elements - including manganese, iron, and copper - often find their way into during the process.

These "contaminants" can give the resulting petrified many interesting colors, including black (carbon), blue (cobalt), green ( copper), red (iron), yellow (manganese oxide), and pink/orange (manganese).

Petrified forests can be found all over the world. Some of the most famous sites in the United States include Petrified Forest National Park in Arizona, Petrified Park in South Dakota, Mississippi Petrified Forest in Mississippi, and Escalante Petrified Forest State Park in Utah.

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The word "petrified" comes from the Greek word petro, which means "rock" or "." Around Halloween, you may hear people say they're petrified. They mean they're very scared of something - scared enough that they've turned to and cannot move! If you ever find yourself petrified, you may be standing as still as a in a petrified forest.

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Do you enjoy learning about the ? Even if history isn't your favorite subject, your imagination has probably been captured by historical events at some point, whether it's the atrocities of World War I or the sinking of the Titanic.

For events that have occurred over the or so, historians are often able to piece together accounts of what took place, using photographs and written accounts. As you look deeper and deeper into the , though, it can be more difficult to get a clear picture of people and events.

Think about the challenge that archeologists and paleontologists face, for example. When they a dinosaur on a in a region of the world, how are they supposed to piece together the history of the creature they've uncovered?

Will they find a or an old photo album? Not likely! Instead, these scientists use careful observation combined with advanced scientific techniques to learn more about these ancient animals. Using the fossilized bones they find, scientists will often try to determine first how old the creature is.

But how can old bones tell scientists anything? One scientific scientists will often turn to is carbon-14 dating. This has proved to be quite accurate for determining the age of ancient artifacts that have a biological origin, such as bones or wood or plant fibers, up to approximately 60,000 years old.

Carbon-14 (a carbon with six protons and eight neutrons) is an isotope of normal carbon, which is also known as carbon-12 (a carbon with six protons and six neutrons). An isotope is an of an that has a different number of neutrons than the common, stable form of the .

Carbon-14 is radioactive and is produced naturally in the atmosphere when cosmic rays collide with nitrogen atoms. When carbon-14 atoms subsequently combine with oxygen, they form carbon dioxide that gets absorbed by plants. When humans and animals eat plants, they take in carbon-14 atoms.

Carbon-14 atoms at a constant rate, because they are radioactive . The rate of radioactive of a substance is defined by its half-life, that is, the time it takes for half the atoms in a radioactive isotope to . Scientists have measured the half-life of carbon-14 atoms to be approximately 5,700 years. At the same time, the environment constantly produces new carbon-14, so that the percentage of carbon-14 in all living plants and animals remains fairly constant.

When an animal dies, it stops taking in new carbon. The carbon-14 it contains, though, continues to , while the amount of normal carbon-12 remains the same. Scientists can then compare the ratio of normal carbon (carbon-12) to radioactive carbon-14 to determine an approximate age of the creature by testing and analyzing its ancient, fossilized bones.

Since the half-life of carbon-14 is about 5,700 years, carbon-14 can only be used reliably to date objects up to around 60,000 years old. You've probably heard scientists talk about things that they claim are millions, if not billions, of years old, though. How did they get those estimates?

Carbon-14 is not the only radioactive isotope scientists can measure and use to date an artifact. Other radioactive isotopes, such as potassium-40, uranium-235, uranium-238, thorium-232, and rubidium-87, have half-lives that extend from millions to billions of years.

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How Do Scientists Know How Old Ancient Bones Are?

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Do you enjoy learning about the ? Even if history isn't your favorite subject, your imagination has probably been captured by historical events at some point, whether it's the atrocities of World War I or the sinking of the Titanic.