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Course: Middle school biology - NGSS > Unit 8
Lesson 2: The fossil recordFossils
Fossils, preserved evidence of ancient organisms, reveal Earth's history. Formed in sedimentary rock, fossils' ages are estimated through layer analysis and radiometric dating. These methods help place fossils in Earth's fossil record, providing a timeline of the evolution of life on Earth. Created by Khan Academy.
Want to join the conversation?
- Is it possible to view the Earth Fossil Record online? (Just for general knowledge!)(23 votes)
- Yes! There should be a website out there to show it.(20 votes)
- where can i find fossils (like a beach, mountain or some other place)?(12 votes)
- You can find fossils anywhere! Beaches, mountains, forests, even your own backyard. You just have to look carefully. Someone even once found Dinasour fossils in his backyard!(18 votes)
- man, science is turning into history(15 votes)
- Is there a 'best' place to find fossils?(7 votes)
- Fossils are easier to find in the badlands because they are typically closer to the surface there.(8 votes)
- That is so cool that she found those fossils! How long does it take for things to fossilize?(9 votes)
- what is the best place to find fossils?(5 votes)
- Anywhere! I'd start on a beach or a woodland. They are everywhere. Your land that your home was built on could have been a nesting ground for a dromaeosaurus. You just need the right gear and right mindset.(3 votes)
- Now I want a fossil
Where can i find a fossil, someone please tell me where I can find a fossil(4 votes)- You can find them literally anywhere. A group of 12-Year-Old students in Australia discovered the Ozraptor. If you have the right gear and the patience you could find a fossil. I like looking whenever I go on vacation.(4 votes)
- I wonder why fossils form(3 votes)
- They form through very specialized conditions. Such as a fly getting stuck in amber.(5 votes)
- what about carbon dating?!?(5 votes)
- how does the fossil stay for so long(4 votes)
- The fossil get's covered by sediment, and some of it's atoms decay. It also becomes a kind of mineral after a very long time.(3 votes)
Video transcript
- [Narrator] When I was 12 years old, I went on vacation to
Alaska with my family. While walking down one of the cold stone covered beaches, I spotted a large pile of rocks that seemed to have slid off the side of one of the hills that connected to the shore. These rocks caught my eye due to their peculiar outer rust color that contrasted with the rest of the rocks on the beach. As I began curiously looking through them, I accidentally knocked a few over. Splitting some in the process. But to my surprise, one of the rocks that split in half had a secret hidden within it. Inside with the imprint
of a tiny pine cone and nearby was rock covered in the imprints of leaves. I was so excited because that day I'd found real plant fossils, but what exactly are fossils and what can they tell us? Fossils are preserved
evidence of organisms that lived in the distant past. They can be made up of
many different things like bones, shells, plants, or even markings like footprints that tell us about an
organism's behaviors. These preserved remains are mostly made possible by specific kind of rock known as sedimentary rock. Sedimentary rock is formed from compressed layers of sediment, which is a mixture of rocks, minerals, and organic matter. Sediment is the result of erosion, which is when bits of rock or soil break down and get
deposited somewhere else. Sediment is deposited in layers, one on top of the other. over millions of years, these layers become compressed, eventually solidifying and forming sedimentary rock. But how do the fossils even get inside of these rocks? Well, let's look back
at the fossil I found. If I had to guess, a long time ago, some leaves and a pine cone must have fallen to the ground and gotten covered in sediment. As more sediment layered on top of them, the plants pressed an imprint of their shape and patterns into the sediment. Over time, the sediment
compressed into rock and the original plant decayed, but its imprint stayed inside the rock. Then finally, my fossil sat until I literally stumbled upon it. So now that we know what fossils are, what can they tell us? As I mentioned before, fossils are like little time machines that can show us what types of organisms where alive millions or even billions of years ago. And they can show us how life on Earth has changed over time. But in order to unlock these secrets, scientists have to estimate the ages of the fossils they find. This can be done in two main ways. Either by looking at which layers of the sedimentary rock the fossils are found in or by using a process known as radiometric dating. Let's talk about layer analysis first. As you know, sedimentary rocks are formed in layers with each new layer forming on top of an old layer. This means that the layers that are closer to the surface tend to be newer than the layers that are deeper in the ground. This means that a fossil found in a deeper layer of undisturbed sedimentary rock will be older than the ones found closer to the top. By looking through these layers, we're able to not only tell how old a particular fossil may be, but we can also look into
the patterns of fossils over multiple layers to see how life on Earth has changed over time. The second way scientists
estimate a fossil's age is through a process known as radiometric dating. Radiometric dating tells us how old a fossil is by studying its chemical properties. Specifically, radiometric dating looks at the decay, or the loss of particles, from certain radioactive
atoms in the fossils. Scientists know how
fast this decay happens. So by measuring the amount of decay that has occurred, scientists can estimate
the age of the fossil. Once scientists know
how old the fossil is, it can then be added to
Earth's Fossil Record. Earth's Fossil Record consists of all the fossils found on Earth along with their relative ages. And it provides us with the big picture view of the history of life on Earth. And with that, you now know how fossils
are formed and dated. Let's go back through the layers of this lesson and go over what we've learned today. Fossils are preserved evidence of organisms that lived long ago. This evidence of life
is most commonly found in layers of sedimentary rock. Now, depending on how deep they are in the layers of sedimentary rock or their results from radiometric dating, fossils can be given an estimated age and be placed on Earth's fossil record. Now, when it comes to the fossil I found, it wasn't a major discovery like the discoveries of the Ichthyosaur, Plesiosaur fossils found by paleontologist Mary Anning, but it made me realize that discovering fossils
is not carried out strictly by professional scientists. You and I can both find fossils too. All we need is a keen eye, some patience, and maybe a little bit of luck.