What are the layers of the Earth?
- crust: outer layer of rock
- mantle:
- solid section between crust and outer core
- near the crust rigid
- deeper causes temperature rise, meaning less rigid and can flow very slowly, behaving like a semi-liquid
- outer core is liquid
- inner core is solid
What is a lithosphere?
- crust and upper part of mantle
- made up of a jigsaw of tectonic plates
- over 100km thick in places
What is the Earth’s surface like and how does it move?
- tectonic plates are rocky rafts floating on the mantle
- plates move about 2.5cm per year
- volcanoes and earthquakes often occur where plates meet (movement of plates against each other causes them)
How can scientists use seismic waves to see what is below the crust?
- s waves travel through the mantle, showing that it’s solid
- s waves not detected in cores shadow, so the outer core is liquid
- p waves move faster through the middle of the core, suggesting the inner core is solid
What is Alfred Wegener’s theory?
- Africa and South America had been one continent which split
- his theory of continental drift supposed about 300 million years ago there was one big supercontinent (Pangaea), that broke into smaller chunks and drifted apart
What evidence supports Alfred Wegener’s theory?
- coastlines of Africa and South America fit together
- fossils of fresh water crocodile in Africa and South America
- matching layers of rock in different continents
- similar earthworms living in both South America and South Africa
Why was Alfred Wegner’s theory not accepted at first?
- theory explained things that couldn’t be explained by ‘land bridge’ theory (e.g. formation of mountains, theory said happened as continents smash into each other)
- the movement of drifted couldn’t be detected so his explanation of how drifting happened wasn’t convincing
What new evidence proved Alfred Wegner’s theory was correct?
- in 1960s scientists investigated the Mid-Atlantic ridge
- finding evidence that magma rises through sea floors and solidifies and forms underwater mountains, that are roughly symmetrical on both sides of ridge (showing the sea floor is spreading, about 10cm per year)
How are convection currents inside the Earth caused?
- radioactive decay creates lots of the heat inside the Earth
- heat creates convection currents in mantle
- causing plates of the lithosphere to move
What are the properties of p waves?
- travel through solids and liquids
- travel faster through solids
What are the properties of s waves?
- travel through solids
- slower than p waves
What is the land bridge theory?
-people believed the continents were liked by land bridges that sunk or were covered by water as the Earth cooled
How did the magnetic orientation of rocks provide evidence for Wegner’s theory?
- liquid magma erupts out of the gap on the sea floor, ion particles in rocks tend to align themselves with Earth’s magnetic field
- every half million years or so the Earth’s magnetic field swaps direction–and the rock on either side of the ridge has bands of alternate magnetic polarity, symmetrical about the ridge
- evidence that the new sea wall was being created and continents were moving apart
