The Structure of the Earth Flashcards
Describe the structure of the Earth
A sphere with a thin rocky crust, mantle and core.
What is the middle of the earth made of?
The core contains iron
What causes volcanoes and earthquakes?
The movement of the tectonic plates.
How fast do plates move?
About 2.5 cm a year.
What happens if you add up all the plate movements over millions of years?
You get continental drift; the continents move around very slowly, India was once part of Africa.
What theory is now used for plate movements?
Plate tectonics is now widely accepted by scientists.
Describe the outer layer of the Earth
Oceanic plates under oceans, continental plates under continents.
What is the lithosphere?
The cold hard bit at the surface, the crust and the top of the mantle.
Why do plates float?
Why do plates float?
Why is studying the Earth’s structure difficult?
We can only drill so far in; the rest is based on seismology, the study of sound waves in the rock that are caused by explosions or earthquakes.
Why is plate tectonics now a widely accepted theory?
It explains a wide range of evidence; it has been discussed/ tested by a wide range of scientists.
Describe the mantle.
The bit between the crust and the core, a semi-solid that is hotter and runnier at the bottom.
What provides the energy for plate tectonics?
Radioactive processes in the core give heat to the mantle. Convection currents then cause the plates to move slowly.
When plates meet, what goes where?
Oceanic plates are more dense than continental so in destructive collisions there is subduction and partial re-melting of the oceanic plates.
At the ocean margins, what goes where?
Plates are cooler at ocean margins and so they sink and pull plates down.
How did the idea of plate tectonics begin?
In 1914 Alfred Wegener proposed continental drift, that the continents were moving, based on evidence from maps and geology. Scientists did not accept this at first.
What other evidence was found that provided evidence for plate tectonics?
New evidence in 1960s, sea floor spreading. The theory of plate tectonics was slowly accepted by the scientific community as subsequent research has supported the theory.
How does magma get to the surface?
Through cracks and weaknesses in rock.
Why does magma rise to the surface?
It is less dense than the rock around it.
How is igneous rock formed?
When molten rock cools.
What is magma anyway?
Molten rock under the earth
What is lava then?
Molten rock that escapes from volcanoes.
What causes different sized crystals in igneous rock?
Different cooling times, fast cooling gives small crystals. Basalt cools quickly and has tiny crystals. Rhyolite/Granite cools slowly, larger crystals. Gabbro cools very slowly, huge crystals.
How does the type of lava affect the eruption?
Iron-rich basalt lava is runny and fairly safe. Silicon-rich rhyolite is often explosive.
Why do people live by volcanoes?
Rich soils, fertile soils.
Why do geologists study volcanoes?
To predict earthquakes, to study earth structure.
How accurate are eruption predictions?
Why?
Better but not 100% accurate. We have greater understanding and can make better analysis.
