C2A - The Earths Structure Flashcards
Describe the crust ?
A thin outer layer of solid rock. Average depth is 20 km
What is the earth made up of ?
A crust A mantle A outer core A Inner core Lithosphere
Describe the mantle ?
The solid section between the crust and the core. Near the crust it’s very rigid but as you go deeper the temperature rises so becomes less rigid and flows very slowly. Basically like a semi liquid
What percentage of the earths radius is the core ?
Just over half
What is the difference between the outer and inner core ?
Outer core = liquid
Inner core = solid
What does the lithosphere include ?
It includes the crust and upper mantle
What is the lithosphere made up of ?
A jigsaw of tectonic plates
Three properties of the lithosphere ?
1) cold
2) rigid
3) 100 km thick
Why is it so hot inside the earth ?
Radioactive decay
Describe convection currents in the mantle
The heat from radioactive decay creates the convection currents in the mantle causing the plates to move
What are big rocky rafts that float on the mantle ?
Tectonic plates
How are tectonic plants able to float on the mantle ?
They are less dense than the mantle
What happens if tectonic plates all moved ?
The continents will move too
Jane is worried her continent will float away from her boyfriends in the next week. Tim reassures her that that won’t happen. How does he know ?
The plates move very very slowly. About 2.5cm a year
How do earthquakes and volcanos occur ?
When plates meet
Why is it difficult to study the inner structure of the earth ?
You can’t get at it directly as the crust is too thick to drill through
What do scientists use to study the earths structure ?
Seismic waves
How are seismic waves produced ?
By earthquakes. Or setting of a man made explosion at the earths surface
How do seismic waves help ?
By measuring the time it takes for the waves to travel through the earth and the location of them scientists can draw conclusions about the earths structure
Name the two types of seismic wave that can travel through earth ?
P waves
S waves
What are the similarities and differences between p and S waves ?
Both travel through solids. But only P can travel through liquid
If S waves are detected in the mantle but not the outer core what does that tell us ?
Mantle is a solid whereas outer core must be a liquid
Scientists realised the inner core was solid. How ?
P waves travel faster through the middle of the core
A long time ago every was confused about the formation of the earth as observations had not been explained. What things confused them ?
1) the fact that fossils of very similar plants and animals had been found on different sides of the Atlantic Ocean
2) why the coast lines of Africa and America fit together
3) why there were fossils of sea creatures in the Alps
Explain the ‘land bridge’ idea
Many people thought continents had been linked by land bridges which had now sunk or been covered by water as the earth cooled
What was Alfred wegeners initial idea ?
Africa and South America had originally been one big continent that split in half
What was wegeners evidence ?
There were matching layers in the rocks in the different continents and similar earthworms were living in both
What is the modern day plate tectonics theory ?
1) 300 million years ago there was a super continent that was called Pangea
2) Pangea broke into smaller chunks. Those are our continents
3) These chunks are still slowly drifting apart
Why did other scientists frown upon Wegeners theory ?
1) He said mountains were formed by continents crashing into each other
2) Drifting explanation was not clear
3) He said continents movement was caused by tidal forces and earths rotation
Later on more evidence was found that explains the sea floor movement. What was it ?
Magma rises up through the sea floor. Solidifies and forms underwater mountains which are kind of symmetrical. Suggesting the seafood spreads about 10 cm a year.
Explain the magnetic orientation evidence ?
Liquid magma erupts out of the gap and iron particles in the rocks tend to align themselves with the earths magnetic field. As it cools they set in position
Every half million years or so the earths magnetic field swaps direction and the Rock on either side of the ridge has bands of alternate magnetic polarity, symmetrical about the ridge
