This lesson is called understanding time scales and is from the unit adaptations, competition, natural selection, and evolution.

Hi there.

My name's Mrs. McCready and I'm here to guide you through today's lesson, so thank you very much for joining me today.

In our lesson today, we are going to describe key events in the history of Earth and we're going to make sure that we can distinguish between billions, millions, and thousands of years ago.

So in our lesson today, we're gonna come across a number of key words, and they're listed up here on the screen for you now.

Now, you may wish to pause the video to make a note of them, but I will introduce them to you as we come across them.

So in our lesson today, we're going to first of all look at the words thousand, million, and billion, and make sure we are well orientated with these words.

Then we're going to have a look at the history of the Earth before we consider what aeons, periods, and epochs are.

So are you ready to go? I certainly am.

So let's get started.

So let's first of all look at the words thousand, million, and billion.

Now, based on all of the evidence that we have available to us, scientists believe that the Earth is 4.

5 billion years old.

That is very old indeed.

And the problem with being 4.

5 billion years old is that that is such a large number it's really difficult to understand what that actually means.

So let's try and unpick it.

Let's start with a thousand, 1,000, one with three zeros after it.

That means it's 10 times 10 times 10 equals 1,000.

Now, we often think of ancient civilizations as being in the very distant past, a very, very long time ago compared to how old the Earth is or how old we are.

But actually, they are extremely recent when we compare them to the Earth, which is four and a half billion years old.

So let's put that into a bit more context.

The earliest human civilizations came into existence about 6,000 years ago.

The Parthenon in Greece was built roughly two and a half thousand years ago, and the Great Sphinx in Egypt was built roughly 4,000 years ago.

The ancient Sumerian stone carving is about the same age.

Now, modern humans first appeared approximately 350,000 years ago.

So it took a very long time for early humans to develop into those ancient civilizations.

And we know that humans first appeared about 350,000 years ago because of fossils that show us early human skeletons and skeletons of predecessors to those early humans.

And if we study those, we get an idea of how long ago those early humans existed.

So let's consider this word thousand again.

How many minutes would it take to count to 100 if you said a number every second? Well, to work that out, we would need to know how many seconds.

So that's 100 seconds if we're saying a word a second and we're counting to a hundred, 100 seconds.

And how many seconds are in a minute? Well, there are 60 seconds in a minute.

And therefore if we divide 100 seconds by 60 seconds every minute, that gives us 1.

7, which means there are 1.

7 minutes in 100 seconds.

So just under two minutes it would take us to count to 100.

So that's the workings for how many minutes in 100 seconds or how long it would take us to count to 100.

Now what I'd like you to do is to calculate how long it would take to count to 1,000 if you said a number every second.

So pause the video and come back to me when you have your answer.

Okay, so how have you worked that out? If you want to count to 1,000 with one number per second, firstly, it would take 1,000 seconds.

Now, there are 60 seconds in every minute.

So if we divide 1,000 seconds by 60 seconds, it will give us 16.

7, which means there are 16.

7 minutes in 1,000 seconds.

So it'll take us just under 17 minutes to count to 1,000 compared to just under two minutes to count to 100.

Well done if you calculated that correctly.

Okay, that's a thousand.

What about a million? So a million is a one with six zeros after it, and we can also say that that is 1,000 1,000s.

So 1,000 times 1,000 is 1 million.

Now, over the last hundreds of millions of years, complex multicellular life has appeared and evolved on Earth.

So that means it's gone from being much simpler to becoming much more complicated and much more highly adapted life on Earth, and that has changed over the course of the last few hundred million years.

And in those last few million years, complex plants have evolved.

We've had the dinosaurs and they've come and gone.

And we've also seen the rise of mammals.

So if you said a number every second, it would take just under 17 minutes to count to 1,000.

So how long do you think it would take to count to a million? Can you calculate it? Is it going to take approximately 11 and a half minutes, 11 and a half hours, or 11 and a half days? Pause the video and come back to me when you've calculated it.

So it takes just under 17 minutes to count to 1,000, but it would take 11 and a half days to count to a million, a thousand thousands.

Well done if you calculated that correctly.

It's quite staggering, isn't it? It's quite difficult to believe.

So that's a thousand and a million.

What about a billion? Because I said that the Earth is four and a half billion years old.

So what is a billion? Well, a billion is a one followed by nine zeros, And we can also express that as 1,000 one millions.

So 1,000 times 1 million equals 1 billion.

Now to count to a billion, saying a number every second, just like we've been showing with thousand and million, it would take us 32 years to count to a billion.

That is astonishing.

So just under two minutes to count to 1,000, 11 and a half days to count to a million, but 32 years to count to a billion.

And in the last several billion years, lots in the solar system has changed.

So firstly, the Earth was formed as the solar system was forming.

Also, the first unicellular, so single-celled organisms appeared, and also the first cells with a nucleus appeared.

So this has all happened billions of years ago.

Not millions, certainly not thousands, but billions of years ago.

So which of the following happened billions of years ago? The first dinosaurs appeared, the first cells appeared, the first human civilizations, or the first fish appeared.

I'll give you five seconds to decide.

So billions of years ago, the first cells appeared.

Well done if you only chose that option.

So what I'd like you to do to summarise thousands, millions, and billions is to put the events listed into the most suitable time periods in the table.

So did these events happen billions of years ago, millions of years ago, or only thousands of years ago.

So pause the video and come back to me when you're ready.

Okay, let's see how you sorted these.

So let's go through the list in order that they were written on the screen and place them in order of time.

So firstly, the formation of the sun happened billions of years ago.

The pyramids were only built thousands of years ago.

The earliest human civilizations happened before that, but still only thousands of years ago.

The first unicellular organisms appeared billions of years ago, and the first cells with a nucleus followed after that, billions of years ago.

Humans developed farming, but only thousands of years ago.

The first dinosaurs appeared millions of years ago.

The first multicellular organisms, so organisms made of many cells and not just one, appeared millions of years ago.

The dinosaurs went extinct also millions of years ago.

The first land plants appeared before the dinosaurs did.

The Earth was formed shortly after the sun was formed.

And the appearance of modern humans was only thousands of years ago.

So have you put them all in their right places? If you need to make any amendments, do so really carefully so it's really obvious where they should be and not just scribbled onto the page.

And well done.

That was quite tricky.

Okay, let's move on to have a look at the history of the Earth.

So we have already seen how the Earth is about four and a half billion years ago, and this is based on the best evidence that we have that we can conclude this approximate figure.

Now, scientists have come up with this number by analysing the age of materials such as rocks and the fossils that are contained within rocks, and they've used a method called radiometric dating to allow that analysis to happen.

So radiometric dating looks at the presence of radioactive elements in the fossils and in the rocks to determine the age of materials, because as radioactive materials age, they become less radioactive, and so that gives us a good idea of how old they actually are.

So based on the evidence of the age of rocks, how old do scientists think the Earth is? Do we think that the Earth is four and a half billion years old, four and a half million years old, or four and a half thousand years old? I'll give you five seconds to decide.

So based on the evidence from the age of rocks, we think the Earth is four and a half billion years old.

Well done.

Now, the first living organisms were unicellular.

That means made of a single cell.

So unicellular organisms, which also did not have a nucleus, they were very basic organisms. And we can collect evidence about these unicellular organisms by looking at stromatolites.

So stromatolites are the oldest fossils that have ever been found, and they were formed from layers of early cells of these early unicellular organisms. Now, the oldest stromatolites that have ever been found are three and a half billion years old.

So scientists estimate that the first cells appeared around 3.

8 billion years ago.

Now, over time, these unicellular organisms, which did not have a nucleus, evolved into more complex forms of life.

So more complex life forms than these early unicellular organisms include single-cell fungi, which first appeared one and a half billion years ago.

So that's 2 billion years after the first unicellular organisms appeared.

Then much more complex multicellular plant life appeared 500 million years ago.

So you can see that we've gone from one and a half billion years for the first fungi to only 500 million years ago for the first land plants.

And these are complex organisms with many cells making up the body of the plant.

And then mammals first appeared 200 million years ago.

So again, significantly more recently than the Earth itself.

Now, modern humans have only been around for 350,000 years.

And so that is just a tiny, tiny fraction of the history of the Earth.

Very recent indeed.

Now, we can see how humans have evolved over time and evolved from predecessor early humans and over a long period of time through the fossil record.

And the youngest fossils that have ever been discovered are only 10,000 years old.

And we have human fossils and early human fossils dating back 350,000 years.

So starting with the oldest, put these events in the correct chronological order.

So that means in order of oldest to youngest.

The first land plants, the first mammals, the first single-celled organisms, and the first fungi, I'll give you five seconds to decide.

Okay, so in chronological order, starting with the oldest, you should have put C, the first single-celled organism, as the first point, then the first fungi, then the first land plants, and then the first mammals.

Well done if you've put them in the correct order.

So I've said already that the Earth is four and a half billion years old approximately.

And if we were to compress all of those four and a half billion years into one single year, we could write onto a calendar the history of the Earth.

So this is the imaginary year of the Earth.

The Earth was formed on the 1st of January, the first living organisms appeared on the 25th of February, and the present day is at the very end of the year on the 31st of December.

So can you put the other events onto the year of the Earth timeline on your worksheet? Put them in the right order.

Can you work out more or less where in the year on the calendar they should go? That's gonna be quite tricky, so pay attention and think carefully.

Pause the video and come back to me when you're ready.

Okay, let's review our work.

So if we have the Earth forming on the 1st of January, then the first single-celled organisms appearing on the 25th of February, then the oldest fossils ever found will appear on the 21st of March.

We'd have to fast forward through the year quite a lot before we get our next event, because the first cells with a nucleus don't appear until the 14th of July.

And the first fungi, not until the 1st of September when we're nearly due back to school.

The first land plants are far further into the calendar than the first fungi, not appearing until the 20th of November.

And then if we zoom into December, we can then add a whole load of extra detail, 'cause most of it has happened in December.

So the first dinosaurs won't have appeared until the 13th of December, the first mammals after that on the 14th of December, and then we have to fast forward all the way to the very end of the year and start putting times in place as well as days, because at 11:19 PM, so nearly 20 past 11 at night, on the 31st of December is when the first modern humans will have appeared, and the youngest fossils ever found will appear at 11:58 PM, so two minutes to midnight, and the present day is at 11:59 on the 31st of December.

Did you get all of those right? It's really mind boggling how long a period of time four and a half billion years is.

Well done if you've got those correct.

And do make some amendments to your work if you need to.

Okay, let's move on to the last part of our lesson now where we're gonna talk about aeons, periods, and epochs.

So what do these words mean and what purpose are they serving in this timeline of Earth history? So scientists have divided Earth's timeline into sections to make it easier to understand, and these really large sections are called aeons.

So we have four aeons, the Hadean aeon, which is the first aeon, the Archean aeon, which follows it, then the Proterozoic aeon, which is next, and finally the Phanerozoic aeon, which we are currently in.

So these are the four largest sections of Earth's timeline and these are called aeons.

Now, if we zoom in to the current aeon, the Phanerozoic aeon, we can see how it is divided into 12 periods.

So 12 sections, these are called periods, and these include the Triassic period, the Jurassic period, and the Cretaceous period.

And I expect you've come across all of those before.

There's also our current period, which started 2.

6 million years ago and is called the Quaternary period.

Now, if we zoom in to the Quaternary period, which is the current period, we can see that it is divided into two smaller sections called epochs, the Pleistocene epoch, which ran from 2.

6 million years ago to 12,000 years ago, and the Holocene epoch, which started 12,000 years ago up to the present day.

However, some scientists suggest that we have now entered a third epoch in this current period because of all the changes that humans are causing to Earth, including by burning fossil fuels, which is causing climate change, and by destructing so much habitat, which is causing a massive loss of biodiversity.

So if we have a look at the Phanerozoic aeon, so this aeon that we're currently in, we can see that there have been five mass extinction events, so mass events that have caused the death of many thousands of species.

So these are called mass extinction events, and there have been five of these in the current aeon.

Three occurred within the dinosaur period, one to start it, one changing between the Triassic and the Jurassic period, and one finishing the dinosaur period at the end of the Cretaceous period, plus two which happened well before that.

Now, the most recent mass extinction event was 66 million years ago.

That was caused by an asteroid which hit the Earth and three quarters of all plant and animal species, including dinosaurs, went extinct.

So that was 66 million years ago.

But some scientists suggest that a sixth mass extinction event may now be in progress, and we have certainly seen lots of species that have already gone extinct and many, many more are endangered due to human activities.

These activities include burning fossil fuels, which is causing climate change, which is leading to extinction of plants and animals, and also habitat destruction, over-hunting, over-fishing, and the pollution of land and oceans.

And all of these activities are driving the loss of biodiversity and therefore creating mass extinction.

So there is reasonable evidence to suggest that we may well be in the middle of a sixth mass extinction event.

So starting with the one that lasts the longest, can you put these chunks of time into order of size, aeon, epoch, and period? I'll give you five seconds to decide.

Okay, so in order of size, you should have started with the aeon and then put period and then the epoch.

Well done if you put them the right order.

So let's consider this sixth mass extinction event again.

And scientists think that a sixth mass extinction event may now be in progress.

That's what our scientist is saying there.

And what I would like you to do is to suggest why some scientists think that this sixth mass extinction event may well be in progress now.

And in your answer, I would like you to describe some of the human activities that could have caused this.

So pause the video and come back to me when you're ready.

Okay, let's review your work.

So I asked you to suggest why some scientists think that a sixth mass extinction event may now be in progress, and I wanted you to describe some human activities that could cause this.

So you might have said that some species have already gone extinct and many more species are endangered due to human activities.

And perhaps you've listed some of those species that have already gone extinct or are on the endangered species list.

Now, some of those human activities which are driving extinction include burning fossil fuels, which is causing climate change, habitat destruction, over-hunting and over-fishing, and the pollution of land and oceans.

So well done if you've included all of those points and extra well done if you've made reference to any animals or plants that you know of that have already gone extinct or are on the endangered list.

Well done.

Okay, we've reached the end of our lesson today, and we have been talking about time scales.

So we have seen that 1 million is 1,000 thousands and 1 billion is 1,000 millions.

We've also seen how we can get evidence for the age of the Earth from rocks and fossils, and we can also get evidence for the evolution and the extinction of various forms of life on Earth.

Now, the evidence from rocks suggests that the Earth was formed 4.

5 billion years ago, and evidence from fossils suggests that the first living organisms, these microorganisms made of one cell only, first appeared around 3.

8 billion years ago.

However, the first land plants appeared only 500 million years ago and the first mammals appeared approximately 200 million years ago.

And modern humans are very recent in the grand scheme of things, having appeared only about 350,000 years ago.

We've also seen how scientists divide this immense amount of time into aeons, periods, and epochs.

So I hope you found that really interesting.

I certainly have.

Thank you very much for joining me today and I hope to see you again soon.

Bye!.