Lesson video

Hi, geographers.

My name's Ms. Hoggett and I'm really excited you're here to learn some geography with me today.

I'm sure if you try your best, you're going to be absolutely fantastic.

Don't worry if you haven't studied this topic before.

I'm here to help you every step of the way.

So our title for today's lesson is "Geological Timescales," and this sits within the Unit: Rocks, weathering, and soil.

Why is geology important? Our learning outcome for today's lesson is that I can explain how geological time is divided and identify the current period and epoch that we live in.

We've got a number of keywords to help us through today's lesson.

Geological time.

The timeline of Earth's history.

Aeon.

The largest division of geological time, lasting hundreds of millions to billions of years.

Era.

A subdivision of an aeon, lasting tens to hundreds of millions of years, Period.

A subdivision of an era, lasting millions of years.

And epoch, the smallest measurement of geological time and a subdivision of a period lasting thousands to millions of years.

So geological time, aeon, era, period and epoch are going to really help us through today's lesson.

Today's lesson is split into two learning cycles.

The first one, understanding geological timescales.

And the second, applying geological timescales.

We are going to start with our first one now.

Understanding geological timescales.

Evidence suggests that Earth is around 4.

6 billion years old.

To help organise this history and make sense of how long it is, Geographers have created geological timescales.

Geological time is much longer than human history.

There wasn't humans on the planet 4.

6 billion years ago.

Geological time is divided into different time periods.

This helps us to understand when significant changes happened and how they relate to each other.

Jacob says, "This is similar to how time today is split into centuries, decades, years, months, weeks, days, hours, minutes and seconds." And he's absolutely spot on.

Breaking geological timescales into smaller sections is useful for the same reason we divide time today into hours, minutes, and seconds.

History is incredibly vast and dividing it into smaller organised units helps scientists clearly identify and study major events such as climate changes and the evolution of life over time.

The structure makes it easier to understand when significant changes happen and how they relate to each other, just as breaking a day into hours and minutes helps us manage daily activities more effectively.

But geological time is not equally subdivided.

Instead, the boundary between one period and the next is determined by major world events.

These can include things like changes to plants and animals.

So when we see new species and when we lose old species.

Tectonic changes, so movements in the Earth's crust.

And climatic changes, so changes to the atmosphere.

Now on the screen here you can see a timeline showing geological timescales.

We've broken it into sections to help us understand when significant changes happened and how they relate to each other.

As we can see on our timeline, we've got our aeons on the left hand side, followed by our eras in the second column, then periods and then epoch.

And we can see that they are not equally subdivided.

To read this, we start from the top and work backwards.

So we can see at the top, we have today's dates, and then as we move further down the table we go further back in history.

The largest division of geological time is called an aeon, and aeons can last hundreds of millions to billions of years.

We are currently in the Phanerozoic Aeon.

The last aeon was known as the Precambrian Aeon and it's divided into three major parts, as we can see at the bottom of our geological timeline.

They started 541 million years ago and extended back to 4.

54 billion years ago so it's a really huge amount of time.

During the first one, the Hadean Era, the environment was very hostile and there was a lot of volcanic activity and meteorite impacts.

The atmosphere was mainly water vapour, carbon dioxide, and ammonia.

It was during this time that the first solid crust began to form.

In our next era, we have the Archean Era, where we had simple organisms such as bacteria beginning to emerge in our oceans.

And we can see some of those simple organisms in the image on the screen.

Finally, we had the Proterozoic Era that followed, where more complex life forms began to evolve.

We had multicellular organisms and there were significant geological changes such as the formation of super continents.

Now this is followed by an era which is a subdivision of an aeon.

Now eras last for tens to hundreds of millions of years, and there have been three eras in the most recent aeon, the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era.

After this, we have a period, and periods are subdivisions of an era that last millions of years.

We're in the Quaternary Period at the moment.

And finally, the smallest measurement of geological time is called epochs.

And these are subdivisions of a period that last thousands to millions of years, and we are currently in the Holocene Epoch.

Now, when we're thinking about geological timescales, we can use the analogy of a 24-hour clock to illustrate the timescales with earth forming at midnight and today being midnight 24 hours later.

So we can see how it's one cycle.

If we start at midnight, we can see that we've got the formation of Earth and that represents zero years.

If we were then to move to 10 minutes past midnight, we are representing 30 million years and that's when our moon was created.

As we move further, and we get to 10 hours and 41 minutes, we can see that that represents 2 billion years, and that's the Great Oxygenation Event.

At 18 hours and 40 minutes, that's 3.

5 billion years, we can see that we had the first plant life.

At 21 hours and 20 minutes, which represents 4 billion years, that's when we saw the first fish appear.

So fish didn't exist for a whole 4 billion years on Earth before they started to emerge.

Then we moved to 22 hours and 47 minutes, or 4.

27 billion years, and that was when we had the first dinosaurs appear.

Then we only had modern humans appear 4.

5 billion years after the world was created.

So what I would like you to do is put these geological timescales in order from largest to smallest.

Pause the video now and have a go at completing this check for understanding.

Well done if you said aeon was the largest, then we had era, then period, and then epoch.

Good work, geographers.

Now as I mentioned earlier, we are currently living in the Quaternary Period.

This period began 2.

58 million years ago.

Sofia says, "We can use mnemonics to help us remember the order of some of the older periods, such as Camels, Often, Sit, Down, Carefully, Perhaps, Their, Joints, Creak.

Notice how the first letter matches to the first letter of those periods starting from the bottom all the way to the top of the geological timescale.

Within the Quaternary Period, we are in the Holocene Epoch.

This began 11,800 years ago following the last ice age.

Let's check your understanding.

So true or false.

We are currently living in the Quaternary Epoch.

Pause the video and have a go answering this question.

Well done if you said false.

We are currently living in the Quaternary Period and the Holocene Epoch, so make sure you get those the correct way round.

They represent a different amount of time.

Now understanding geological timescales helps geographers to understand major events such as mass extinctions, climate change and evolution.

Laura says, "It helps us to understand how Earth has changed and will continue to change in the future." So we're now going to check what you've learned so far with a practise task.

There's two parts to this.

Firstly, I'd like you to complete the table by adding on the correct labels.

Epoch, era, period, aeon, Quaternary, and Holocene.

And the second part to this, is how long ago did our current period and epoch begin? I'd like you to answer both of those questions in full sentences.

Pause the video and have a go at completing this practise task.

Well done for giving that a really good go, geographers.

I'm sure you've done fantastically, but let's check your answers.

So for the first part, we needed to complete the table by adding on the correct labels.

Epoch, era, period, aeon, Quaternary and Holocene.

Now you can see on the screen we've completed this for you.

So we have aeon on the left as the largest subdivision of geological time.

Then we have era, period, and epoch.

And under period we've put Quaternary because that's the current period we are in.

And under epoch we've put Holocene in that top box 'cause that is the epoch that we are in.

Good work, geographers.

For the second part, we needed to think about when our current period and epoch began.

So our period began 2.

58 million years ago and our epoch began 11,800 years ago.

So well done if you've got those spot on.

You are doing fantastically today, geographers.

I know there's a lot to take in, but we are ready to move on to our second learning cycle, which is about applying geological timescales.

So geological periods represent clear intervals of Earth's history that are characterised by significant changes in the planet's geology, climate and life forms. Over geological time, plate tectonics have changed.

In the Permian Period, we had one super continent called Pangaea.

Since then, continents have collided, combined, and split apart to form the continents we have today.

So this is where we had our super continent in the Permian Period.

Followed by how it started to split in the Triassic Period.

Then we have more splits and more changes in our Jurassic Period, followed by again much more divisions in our Cretaceous Period.

And then in what we know today, in our Quaternary Period.

So we can see that due to movements under the Earth's crust and different forces, our plates have begun to move around the Earth, shifting those continents.

Now over geological time, temperature has changed which has impacted global sea levels.

So we can see on the graph that we have on the screen, we have how many millions of years ago we're referring to, followed by the name of the period.

During warmer periods, ice has melted and flooded the land, and during colder periods, there have been ice ages and sea levels have fallen.

Now each period is marked by changes to species that had lived through them.

And on the screen we can see a timeline presented slightly differently to how we saw it earlier, but it shows the different types of animals and species that we found living in those different periods.

We can also see on there when the two major extinction events were, which changed those areas that we're referring to.

So I would like you to have a go at completing this practise task.

And I'd like you to complete the missing words in these sentences.

One, geological what represents clear intervals of Earth's history? Two, over geological time, what has changed which has impacted global sea levels? Three, each period is marked by changes to what that had lived through them.

Pause the video and have a go at completing this check for understanding.

Well done for giving that a good go, geographers.

Let's check your answer.

So geological periods represent clear intervals of Earth's history.

Over geological time, temperature has changed, which has impacted global sea levels.

And each period is marked by changes to species that have lived through them.

You're doing such a brilliant job, well done.

Now in the Proterozoic Era, Earth was almost completely frozen.

It was also when the great oxygen event took place, which enriched the atmosphere with enough oxygen to support life.

Laura says, "In 1992, geophysicist Joseph Kirschvink called this era 'The Snowball Earth.

'" He said this because during this era, Earth underwent global glaciations where it's thought the ice covered the entire planet.

He built his hypothesis on these early ideas about widespread glaciation, but he framed them in a way that was a bit easier for everybody to understand.

In the Paleozoic Era, we saw life start to diversify.

In this era, we started to see fish and amphibians being developed.

And so did vast forests which formed today's coal.

Unfortunately, the era ended with major extinctions and the exact cause of these are debated.

Some people believe it to be volcanic activity that caused the extinctions.

Other people believe it to be things like climate change, or some even say it could have been a meteor impact.

So some people disagree on what the cause was, which is why it's still debated.

Now, fossils from the Paleozoic Era provide evidence of the life forms that existed.

So we had Trilobite fossils found at the Grand Canyon and Brachiopod fossils found at the Grand Canyon as well, which indicate the type of species that were living through this era.

Now Trilobites are arthropods and they're similar to many invertebrate animals that live today, including spiders and insects, and crustaceans like shrimps, crabs, and lobsters.

In this case, geologists know that these ones were marine animals like the Brachiopods, which are also marine invertebrates, which means they have no backbone and are one of few animal groups that only live in the ocean.

So that tells us a lot about the type of climate and landscape that we had during the Paleozoic Era.

Next we have the Mesozoic Era known as the Age of the dinosaurs.

The climate was warm enough and wet enough to be able to sustain conifer trees and grasses, but unfortunately, the era ended with the largest extinction event in the history of the Earth, which is why we no longer see dinosaurs on Earth today.

But dinosaurs skeletons help us to understand the Mesozoic Era, and help us to understand what we likely saw walking on Earth at that time.

For example, we can see we have a Triceratops skeleton on the screen and also a skeleton of a Tyrannosaurus Rex.

And lastly, the Cenozoic Era is our current era, and this is where we saw humans first start to walk on Earth and mammals diversified into the animals that we know today.

Some of the earliest mammals in the Cenozoic Era included mammoths and mastodons, and we can see them on the screen.

So we have a skeleton of America mastodons, and we also have an artist interpretation of a mammoth.

So let's check your understanding.

In which geological time period did dinosaurs become extinct? Was it A, Jurassic.

B, Cretaceous.

Or C, Triassic.

Pause the video and have a go at completing this check for understanding.

Well done if you said B, Cretaceous Period.

We know that's when the dinosaurs became extinct.

So some scientists have recently suggested that Earth has actually entered a new geological epoch, the Anthropocene.

This is said to be caused by the following human activities that have significantly altered the planet.

So plastic pollution, human induced climate change, and urbanisation.

So these three things have had such a significant impact that some scientists think that we're actually moving into a new epoch where we have new world events.

However, this is actually contested.

Laura says, "Some scientists argue that the evidence isn't strong enough to define a new epoch." Where Aisha says, "Others debate when it should officially begin." So there is some controversy over whether we've moved into a new epoch, but some scientists argue we call that the Anthropocene.

So we're now gonna practise what you've learned in this second learning cycle.

So you've got two parts to this practise task.

I would like you to place the icons onto the correct place on the timeline, so that we know what species existed within each period.

And then we are going to explain why some scientists suggest we are moving into a new epoch, the Anthropocene.

Pause the video and have a go at completing this practise task.

Well done if you gave that a really good go.

So if we take a look on the screen, we can see that icons correctly placed onto the timeline, are dinosaurs in the Mesozoic Era, and we can see that we have early species in the Paleozoic Era, and in Cenozoic Era we can see we have things like mammoths and our mastodons.

And then for part two, we needed to explain why some scientists suggest we're moving into a new epoch, the Anthropocene.

So we could have said, "Some scientists believe we're entering a new epoch called the Anthropocene because humans are having a huge impact on earth.

The current epoch, the Holocene started 11,700 years ago after the last ice age.

However, some scientists think our actions have changed the planet so much that we need a new epoch.

Humans have altered Earth's climate by burning fossil fuels, which releases greenhouse gases and causes global warming.

We have cut down large areas of forest, polluted the oceans with plastic, and changed the landscape with cities and roads.

Many animals and plants are becoming extinct because of human activity." So if you said something along those lines, you've done a fantastic job, and we can see that whilst some scientists suggest that we're moving into a new epoch, the Anthropocene, we know that some argue that there isn't enough evidence for that.

So this is still a contested idea.

Well done, geographers.

You have done brilliantly today and you've come to the end of learning cycle two, which means we've reached the end of our first lesson looking at geological timescales.

To summarise, we've seen today that geological timescales are measured in millions of years.

A period is a basic unit of geological time, and they last for millions of years.

An epoch is a subdivision of a geological time period, and we are currently in the Quaternary Period and the Holocene Epoch.

Although some people think we're moving into a new geological epoch, the Anthropocene.

Thank you so much for your hard work and effort today, geographers.

You've been brilliant.

And I look forward to seeing you soon in our next lesson.