1. The Earth’s Structure Thursday, 22 November 2018
L.O: to know about the structure of the earth and how tectonic plates effect us.
Thursday, 22 November 2018

2. Starter Could we dig a hole to Australia? Discuss with your partner…
So, could we?
Chances are – no. In fact, if we did, we’d need lava-proof tubing, and with the forces of gravity we’d keep going up… and down again, at an extraordinarily fast pace – I think I’d prefer the 20 hour flight!
Click on the picture to watch the video…

3. Layers of the earth
The Earth is almost spherical and it has a layered structure.
The bit we live on, the crust, is very thin (it varies between 5 km and 50 km) and is surrounded by the atmosphere.

4. Layers of the Earth
At the centre of the Earth is the core, which we think is made of iron and nickel.
The core is the thickest layer of the Earth.

5. Layers of the earth
Surrounding the core is the mantle. The mantle is about 2900 km thick and has all the properties of a solid, except that it can flow very slowly in convection currents.
These convection currents are caused by the large amounts of heat produced by radioactive decay in the core below.

6. Layers of the earth
So what are the labels for these different parts of the earth?
Click on the boxes to reveal the labels.
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7. The Earth’s Resources
The Earth's crust, oceans and atmosphere are the ultimate source of minerals and resources — we can get everything we need from them.
The Earth’s resources:
Metals like gold and silver can be mined from the Earth's crust.
We can get salt from the Earth's oceans.
Gases like oxygen and nitrogen can be extracted from the atmosphere.
Silver being mined from the Earth's crust.

8. Tectonic Plates
The crust and the upper part of the mantle are cracked into a number of large pieces called tectonic plates. These plates are a bit like big rafts that ‘float' on the mantle.
The plates don't stay in one place though. That's because the convection currents in the mantle cause the plates to drift. The map shows the edges of the plates as they are now, and the directions they're moving in (blue arrows).

9. Tectonic Plates
Most of the plates are moving at speeds of a few centimetres per year relative to each other. Occasionally, the plates move very suddenly, causing an earthquake. Volcanoes and earthquakes often occur at the boundaries between two tectonic plates.
Don't panic! You don't need to know the names and locations of the plates for your exam. As long as you get the general concept you'll be fine.

10. Predicting earthquakes
Tectonic plates can stay more or less put for a while and then suddenly lurch forwards. Earthquakes are impossible to predict accurately because we can't see what's happening deep underground, but scientists are trying to find out if there are any clues that an earthquake might happen soon — things like strain in underground rocks.
Scientists can use these clues to predict that an earthquake will happen, but these predictions are sometimes ignored by local people and governments. Here are the reasons why.

11. Not always right
Even with all their clues scientists can only say that an earthquake's likely to happen, not that it definitely will happen. Scientists make many earthquake predictions every year and not all of them are right.

12. Never exact
If the earthquake does happen, it's impossible to predict exactly when. The earthquake could happen months after the initial prediction.

13. Can’t predict the damage that’ll happen
There's no way to accurately predict the strength of the earthquake. Many earthquakes cause little or no damage.

14. don’t know where it’ll happen
Scientists can't accurately predict exactly where the earthquake will happen — it could be miles away from where it was initially predicted to happen.

15. No way to stop it
There's no way to stop an earthquake, so the only way that people can respond to a predicted earthquake is to evacuate. This is expensive and very inconvenient, so people don't want to do this unless they are sure that the earthquake will happen imminently & where they live and will be strong enough to cause serious damage and put their lives at risk.

16. Predicting volcanic eruptions
There are some clues that say a volcanic eruption might happen soon.
Before an eruption, molten rock rises up into chambers near the surface, causing the ground surface to bulge slightly.
This causes mini-earthquakes near the volcano. But sometimes molten rock cools down instead of erupting, so mini-earthquakes can be a false alarm.

17. Questions – Fact Recall
What is the outer layer of the Earth (the bit we live on) called?
Describe the properties of the mantle in terms of whether it is a solid or a liquid.
What do we think the Earth's core is made from?
What drives the movement of tectonic plates?
How quickly are most tectonic plates moving?
Where do earthquakes and volcanoes usually occur?
Give three things that scientists cannot accurately predict about an earthquake.

18. Answers – Fact Recall The crust
The mantle has all the properties of a solid except that it can flow very slowly.
Iron and nickel
Convection currents in the mantle.
Very slowly — speeds of a few cm per year.
At the boundaries between tectonic plates.
E.g. exactly when the earthquake will happen, exactly where the earthquake will happen and how strong the earthquake will be.

19. Questions – Application
Catania is a city in Italy that is located near to an active volcano. In the last few days there have been some mini-earthquakes in the city and some of the residents are starting to evacuate.
Why are some of the residents evacuating?
Suggest why not all of the residents are evacuating.
Palmdale is a city in the USA. It lies on the San Andreas Fault. Lots of earthquakes happen in Palmdale. Explain why.

20. Answers – Application
The mini-earthquakes could be a sign that the volcano is about to erupt.
E.g. The mini-earthquakes could be a false alarm and evacuating is very expensive/inconvenient.
Earthquakes occur when tectonic plates suddenly move, so they often occur at boundaries between tectonic plates. Palmdale is located on the boundary between two tectonic plates and so it will get lots of earthquakes. 1.