How Old is the Earth_ Part 1_2

Hello, my name is Marla and I'm a science teacher here at Fun Science Demos. Welcome! Many people wonder, how old is our earth? What kind of evidence have scientists collected to determine the age of our earth? There are two types of scientists that study the age of our earth. The first type of scientist is called a geologist and those scientists study rocks. The second type of scientist is called a paleontologist and those scientists study fossils. Fossils are impressions of living things that are left inside rocks that are formed inside special types of rock. This special type of rock can be formed at the bottom of oceans, rivers, or lakes. Here, let me show you one. This looks like an ordinary rock but when it's split open it actually reveals a special kind of animal called a trilobite. Here, let's actually zoom in a little bit closer. Look how cool! We can actually see the eyes of the trilobite right here and its body segment up here. It's really hard to see but there's actually another fossil over here as well. The oldest trilobite fossils that have ever been found lived about 500 million years ago, which is approximately right here on our timeline. The main evidence that scientists use to figure out the age of our earth are fossils and the ages of certain types of rocks. Scientists have found that our earth is very, very old. Not thousands, not millions, but billions of years old. Take a look at this timeline that we made to help you understand just how old our earth is. We've zoomed in so you can see our timeline just a little bit closer. Each tiny line you see here is one millimeter and one millimeter represents five million years of time. In this first portion right here, we have 200 millimeters which represents one billion years. By studying the oldest rocks that geologists have found here on earth and rocks that have been found on the moon and in meteorites, geologists estimate our earth is about four and a half billion years old. We have marked some of the major milestones of life on our planet here on the timeline and also have a scale to show you how small life was in the beginning. In the first billion years, the earth was cooling down and eventually water vapor was turning into liquid water and forming the oceans. In the first billion years, paleontologists didn't find any fossils and rocks that were that old. Some of the oldest fossils that paleontologists have found occurred when the earth is about 1.1 billion years old. These fossils have been found in rocks located in western Australia and in Greenland. These fossils were very tiny, about the size of bacteria that are alive today, but all life back then was only in the oceans. When the earth was about one to two billion years old, there were a lot of tiny fossils and life was very small. This scale right here shows a line that is about the width of a human hair or about one-tenth of a millimeter. Scientists that study really small life divide one millimeter into a thousand parts and each part is called a micron. The scale right here on the card is about 100 microns long. So these fossils are about one to ten microns big. All of this life is between one and ten microns and is very similar to bacteria cells that are all over our earth today. So the only life on earth back here was in the ocean and very small. If we look at how life changed and evolved from the time the earth was two to three billion years old, it's still very small, but in the fossil record we start to see larger cells. Cells that have other parts inside of them and are more complicated. As the earth reached about three and a half billion years old, life started to get even bigger. Life was still in the ocean and still much smaller than the plants and animals that are alive today. Then in the fossil record, as the earth approaches about four billion years old, paleontologists start to see more variety of living things and are getting bigger and bigger in the fossil record. Rock layers all over the earth reveal the same pattern of fossils. Living things are becoming bigger, more complex, and more different. Geologists and paleontologists have named this period of time right here the Cambrian explosion. So there wasn't a real explosion or anything like that, but compared to what living things had looked like for the past three billion years, there was an explosion of fossils in the rocks all around the world and in the same layers of rocks around the world. Here are some of the different types of fossils that we found since the Cambrian explosion. Fish, amphibians, reptiles, land plants, dinosaurs, and mammals. Human-like fossils have just been found in the last four million years of earth's history. That's less than one millimeter on this timeline. Life has certainly changed and evolved over the last four and a half billion years. It's just so cool and the evidence we have comes from fossils and the ages of rocks. In the next part of our series on the age of our earth, we are going to examine the fossil record starting with the Cambrian explosion. We are going to show you some amazing fossils that have been found by paleontologists. There is an important point to know before we end. When we find fish fossils in rock layers this old, we never find fish fossils in rock layers that are older than that rock. We only find fish fossils in rock layers that are newer. Science is so cool, especially when you can look back in time and look at fossils after you split open a rock. Thanks for watching.