Lesson video

Welcome to this lesson from the Oak National Academy.

Today's lesson is called The Fossil Record Provides Evidence for Evolution, and it is taken from the unit Fossil Evidence, Selective Breeding and Explaining Evolution.

Hi there, I'm Mrs. Wheat, and I'm gonna be your teacher for today's lesson.

By the end of today's lesson, you'll be able to describe how the fossil record provides evidence that the features of species change, evolve over time.

Let's have a look at our keywords.

So we have fossil.

Fossils are the mineralized remains of once living organisms or of tracers left behind by organisms. Fossil record, all the fossils ever found and their ages provide a body of evidence called the fossil record.

Extinct, an extinct species has no living members.

Evolution, the process in which the characteristics of species change over many generations, sometimes becoming new species.

So I'll be quiet for five seconds so you can read through those again, or if you wanna copy them down, I suggest pausing so you've got enough time to do that.

Today's lesson is in two parts.

The first part is about the fossil record.

We'll talk about what the fossil record is, all about fossils, why they're important and what they can tell us.

Then in the second 1/2 of the lesson, we'll talk about how fossils provide us evidence for evolution.

So showing that species change, the characteristics of species change over time.

First of all, let's talk about the fossil record.

Fossils are the mineralized remains or traces of once living organisms. So we'll look at kinda the first type of fossil.

So that happens through mineralization.

So you have the remains of an organism, maybe a plant or an animal, and over thousands of years, the remains get replaced by these minerals in the water.

So minerals are compounds of elements like carbon or calcium.

So these are all fossils that are formed by mineralization.

So we've got a trilobite fossil, really famous example of a fossil you might have heard of.

So those are invertebrate, an invertebrate group of species that lived millions of years ago.

We've got ammonite fossils, another group of species that live millions of years ago.

But what's really cool about these guys is that you can find them in the UK.

You can find fossils of these all over the UK, particularly in the Jurassic Coast, which is along the south coast of Britain in places like Dorset.

And wood plants can be petrified as well.

So petrified wood is an example of a fossilised plant.

So those are all examples of body fossils.

You can also have tree fossils.

So this is some imprint of some leaves.

We've got a dinosaur footprint, those counts as fossils as well.

And we've got some fossilised eggs.

Again, another type of fossils, but those will count as trace fossils, as opposed to body fossils.

All the fossils ever found along with their ages provide a body of evidence called the fossil record.

The oldest fossils recorded are stromatolites, and they were formed from layers of the earliest microorganisms billions of years ago.

The oldest stromatolites and also the oldest fossils are around 3.

5 billion years old.

Isn't that incredible? The youngest fossils are around 10,000 years old.

Now, this is because the process of fossilisation takes thousands of years.

So if we have the remains of an organism that lived maybe 2,500 years ago, they likely wouldn't become fossilised yet because the process of fossilisation takes around 10,000 years.

So that's why the youngest fossils are around 10,000 years old.

Some of the youngest fossils discovered are from woolly mammoths, and you can see in the photos an example of a fossilised woolly mammoth.

And hopefully you get a sense of the scale of just how big these animals were compared to this person in the photo.

Let's have a look and see if you understand the key points around the fossil record.

Complete the sentences about the fossil record.

All the fossils ever found and their blank provide a body of evidence called the fossil record.

The oldest fossils are stromatolites, which are roughly 3.

5 blank years old.

The youngest fossils are roughly 10 blank years old.

Take five seconds now or pause the video if you need some more thinking time.

Click play when you're ready to see the answers.

Let's have a look at the answers.

All the fossils ever found and their ages provide a body of evidence called the fossil record.

The oldest fossils are stromatolites, which are roughly 3.

5 billion years old.

The youngest fossils are roughly 10,000 years old.

Great work if you've got those right.

So we find fossils in sedimentary rock, and that's rock that's made from layers that build up on top of each other.

And then immense pressure turns into rock over thousands of years.

Because of the way sedimentary rock forms with those layers building on top of each other, the oldest rock is lower down and the newest rock is higher up.

So here, we've got a cliff face of sedimentary rock.

The oldest rock is at the bottom, lower down, and the newest rock is towards the top.

So fossils deeper down in the oldest layers of rock are of simpler organisms, many of which are now extinct.

So let's think back to the oldest fossils.

The oldest stromatolites are about 3.

5 billion years old.

So you'd find those in really, really deep layers of rock.

Fossils found higher up in newer layers of rock are much younger.

They are often from far more complex organisms that are more similar to those that exist today.

So here, we've got an example of an Archaeopteryx fossil, and they existed millions, well, around 140 million years ago.

And while you might be thinking this doesn't look like anything I've seen today, compared to stromatolite fossils, you can see that this has got a skeleton.

You might be able to recognise a backbone and a head and limbs, so much more similar to the animals that we have on the planet today.

Let's see if you understood that.

This cliff base is made of chalk, a type of sedimentary rock.

Where in this cliff would you most likely find the oldest fossils? Is it A, B, C or D? You can take five seconds, or if you need some more thinking time, click pause.

Click play when you're ready to see the answer.

The answer is D.

So you'd find the oldest fossils in the oldest layers of rock.

Because of the way that sedimentary rock forms, the oldest layers of rocks are further down, lower down on the cliff face.

Well done if you got that right.

So studying fossils provides evidence about the original organisms, including information about their size.

So if we look at my example on my photo here, this is some ammonite fossil.

And although the fleshy parts of this will have decayed, the shell still remains.

So we can use the shell to make educated guesses about the overall size of this organism.

We can know the shape, again, if we look at the shell.

The shell's really, really well preserved, and we can see the spiral details on this, on this organism.

We can make inferences about what the body structure of this organism might have been like by comparing this organism to other shell organisms that exist still today.

And we can, through techniques like carbon dating, we can estimate the time period that organisms lived in.

We can even draw conclusions about the habitats in which the original organisms lived in based on where the fossils are found.

So if you found these fossils in an area that you knew when this fossil's around, millions of years ago, this was deep under the ocean, then you can pretty safely conclude, okay, well, this was a marine organism.

And you can also infer information about food chains.

Sometimes, you have fossilised remains of an organism trapped inside another organism, and that means that it's likely that, okay, this organism ate that organism, and from that, you can start to construct a food chain.

The fossil record provides evidence about the characteristics of organisms that lived a long time ago.

And often, this is the only evidence we have about these organisms. If we look at this photo, we can see the fossilised skeleton of a Stegosaurus nicknamed Sophie.

And you can find this in the Natural History Museum in London.

There have only been around 10 fossilised skeletons of Stegosauruses found, yet we know so much about this organism.

Most dinosaur obsessed primary school kids can tell you what a Stegosaurus is, and that's all based on only 10 skeletons that we've found.

Comparing fossils to living organisms show us how species have changed.

And from this, we can draw conclusions about how they have evolved over time.

For example, we can look at the ancestors of the modern horse, and that can help us to understand how and why they evolved over millions of years.

Some fossils are of organisms unlike anything still alive on Earth, and these species have gone extinct, which means that there are no living members of the species around anymore.

Why some species go extinct and others don't is a really interesting question, and fossil evidence can often help us answer it.

Let's check and see if you understood that.

Is this statement true or false? Fossil evidence shows us that many species have gone extinct.

Take five seconds, or you can pause the video if you need more thinking time.

This statement is true.

Justify your answer.

So why is this statement true? Is it true because many fossils are of species that no longer exist, or deeper sedimentary rock layers contain older fossils? Take five seconds, or pause the video if you want more thinking time.

A is the correct justification for this statement.

Many fossils are of species that no longer exist.

Well done if you got that right.

Well done on your hard work so far.

This is the first practise task of today's lesson.

Laura has written some notes about fossils, but there are some mistakes.

Identify the mistakes and rewrite her notes.

So she's written fossils form when the remains of organisms turn to rock over thousands of years.

Only animals can become fossils.

The oldest fossils are 3.

5 million years old.

The youngest fossils are 10 million years old.

Fossils are found in igneous rock.

You find older fossils in layers of rock closer to surface.

So you'll need to pause the video now to give yourself enough time to think about these statements and to rewrite them.

Click play when you're ready to see the answers.

Good luck.

Let's see how you did.

So fossils form on the remains of organisms. So they don't turn to rock, they mineralize over thousands of years.

Any organism, not just animals, can become a fossil.

The oldest fossils are 3.

5 billion years old.

The youngest fossils are 10,000 years old.

Fossils are found in sedimentary rock, not igneous rock.

And you find more recent or newer fossils in layers of rock closer to the surface.

Well done if you've got those right.

So we've talked about the fossil record, what fossils are, what the fossil record is and why it's important.

Now we're gonna talk about how fossils show that species change over time.

So fossils show us that organisms can change, evolve over time.

We can see from fossilised bones that some species such as horses have undergone some changes over the last 50 million years.

So if we look at my diagrams below, we've got the lineage from the modern horse.

And we can see that the modern horse evolved from a really small creature that had four toes and a really small skull.

And slowly over millions of years, the number of toes reduced.

So modern horses run on one large toe.

And their skulls got bigger and their teeth changed and got bigger.

And that's all to do with being more suited to their environment now.

So that's just one example of how species have changed over time.

We're gonna look at another one in much more detail.

So we're gonna talk about whales.

So whales have undergone really large changes.

They've not just gotten a bit bigger, changed their teeth, chased their skulls a bit.

They've gone through some really, really huge changes.

So fossil evidence shows us that whales share a common ancestor with hoofed animals, such as pigs, camels or hippos.

So this suggests that whales evolved from land animals.

Baleen whales are among the first group of whales still alive today to evolve.

And so we're gonna have a look at that process of how an organism that lived on land eventually evolved into the whale that we know today.

Whales are a really well researched example of how species have changed or evolved over time.

And this is because many fossilised skeletons of the early ancestor of the modern whale have been discovered.

Fossil evidence suggests that whales evolved from a small land mammal.

Our diagrams here show the skeleton of this small land mammal, the Indohyus, and an artist impression of what we think that might look like.

Let's check to see if you understood that.

Fossil evidence shows us that, A, no species have gone extinct, B, species change over time, or, C, species do not change.

You can take five seconds to think about which the correct answer might be, or you can pause the video if you need more thinking time.

Okay, the correct answer is B, species change over time.

Well done if you got that right.

So I'm gonna give some background and some context to the evolution of the whale.

So approximately 66 million years ago, there was a mass extinction event that killed the majority of planet animal life on the Earth.

This included most species of dinosaur.

This provided an opportunity for other animals to thrive as there were now fewer predators, especially in the sea.

So lots of the predatory lizards that lived in the seas and oceans were now extinct.

And so now other animals weren't being hunted, so they had a chance to thrive and really increase their populations.

So fossil evidence suggests that whales were some of the first mammals to go into the sea.

Fossil evidence suggests that Indohyus, the early ancestor of the whale, evolved into a form such as Pakicetus, which lived 50 million years ago.

And Pakicetus are named because they were found in Pakistan.

Pakicetus were land mammals that had some adaptations that helped them spend some of their time in the water.

A later evolutionary stage was Ambulocetus.

So these were amphibious mammals that lived 49 million years ago.

And we can see, if we look at their feet, they've now changed.

They've evolved to be broad like a paddle, and this aided swimming.

So we still have two quite similar organisms. We've still got four limbs, but now we've got feet and legs that are better adapted to swimming.

Further evolution led to the Dorudon, which were marine mammals that lived 40 million years ago.

The front legs had evolved into flippers.

Unlike the Pakicetus and Ambulocetus, their back legs were no longer functional.

So we've still got four limbs, but those last, those back limbs aren't really doing much.

And the front limbs really are flippers now, as opposed to legs.

It wouldn't be able to support itself on land.

And here we have something you'll recognise as the skeleton of a whale.

So baleen whales were some of the first whales to evolve around 34 million years ago.

So that's the evolutionary history of the whale.

It's a really interesting evolutionary history as it goes from a small land mammal with four limbs, slowly becomes amphibious over millions of years, and then finally becomes the marine mammal that we recognise today.

Most organisms haven't undergone such a dramatic change, even though those took millions of years.

So the whale is a particularly interesting example of evolution.

Fossils are often incomplete or broken when they're found.

And so to understand what the original organism looked like, scientists have to interpret the available fossil evidence, draw upon their own expertise and judgement and use a bit of imagination.

So this would be something like the fossil evidence that you'd find from Pakicetus.

You can see that not all of the bones are there.

So we've not got a complete skeleton.

So what a scientist might do then is fill in the gaps, have a look at modern animals, similar animals, and try and make educated guesses and inferences about what the complete skeleton would look like.

And then we have an artist interpretation of what Pakicetus might have looked like, which again is based on the skeleton, is based on other animals that we've seen today, but isn't necessarily exactly what the original organism looked like.

Let's see if you understood that.

Put these pictures in the correct order to show how whales have evolved over time.

So you can take five seconds, or you can pause the video if you need some more thinking time.

Click play when you're ready to see the answers.

Okay, let's have a look at the answers.

So first we had Pakicetus.

We have a small land mammal that walks on four limbs.

And then we have Ambulocetus.

It looks almost like a crocodile.

You can see that its feet now are adapted to be paddle-like, helps it in the water.

Then we have the Dorudon, still has four limbs, but really back two legs aren't doing much.

And the front two, and the front two limbs are really flippers, as opposed to legs and hands that'd be able to support itself on land.

And finally, we have the baleen whale, which evolved 34 million years ago.

It's got a tail fluke at the back.

It's got two enlarged front flippers.

This thing could not walk on land.

This is definitely a whale.

Well done if you got that right.

This is the final practise task of today's lesson.

Jacob is learning about fossils in school.

He says the fossil record shows us that organisms always remain the same.

Explain why Jacob is incorrect.

Use whales as an example of how species change over time in your answer.

So you'll need to pause the video now to give yourself enough time to think about the answer and to write it down.

Click play when you're ready to see the answers.

Let's have a look at the answers.

So the fossil record shows us that species evolve or change over time.

Older fossils found in deeper layers of rock are of older and simpler organisms, which have often gone extinct.

Newer fossils found in layers of rock closer to the surface are from more recent and much more complex organisms. Whales are a really well researched example of how species change over time will evolve.

Whales evolved from smaller land mammals, and over millions of years, they gained adaptations that allowed them to become marine mammals.

Well done if you got that right.

Brilliant work today.

Let's summarise what we've learned to help it stay in our memories.

All the fossils ever found along with their ages provide a body of evidence called the fossil record.

The oldest fossils are 3.

5 billion year old fossilised stromatolites.

The youngest fossils are just 10,000 years old.

Fossils show that some species have gone extinct.

Fossils show that the features of some species have evolved over time and whale are a really well researched example of how the features of a species can change over time.

Again, great work today.

Good job on all your hard work.

Take a break now, and I'll see you hopefully really soon for our next lesson.