Earth structure Flashcards
What are the 4 main layers of the earth
inner core, outer core, mantle, crust
Describe inner core
inner core forms the centre of the Earth and is 1400 km across. The inner core is solid and dense; in fact, it is over five times denser than rocks on the surface. The inner core is made up of iron (80%) and nickel and has a temperature of around 5500°C.
Describe the outer core
Surrounding the inner core is the outer core. The outer core consists of dense, semi-molten metal and is around 2100 km thick. The temperature of the outer core is between 5000 and 5500°C.
Describe the mantle
Outside the core is the mantle. The mantle is a semi-molten layer around 2900 km thick. It is less dense than the outer core.
Describe the crust
The crust forms the surface of the Earth. The crust is divided into large sections called tectonic plates. Tectonic plates can be either oceanic, continental or a combination of both
3 evidence for tectonic plates moving
Convection currents occur in the mantle. These convection currents move heat from the interior of the Earth towards the surface.
As the semi-molten rock in the mantle is heated, it becomes less dense than its surroundings and rises. As it reaches the crust above, it spreads out carrying the plates above with it. As the semi-molten rock then cools, it gradually sinks back down to be re-heated.
Another explanation for plate movement is ridge push. Newly-formed plates at oceanic ridges (constructive plate margins) are warm, and so have a higher elevation at the oceanic ridge than the colder, more dense plate material further away; gravity causes the higher plate at the ridge to push away causing the plates to move away from each other.
Additionally, at destructive plate margins the denser, oceanic plate sinks into the mantle under the influence of gravity, which pulls the rest of the plate along with it. This is known as slab pull.
What is the point where plates meet
The point where plates meet is known as a plate boundary or margin.
how do destructive plate boundaries form
When an oceanic and continental crust move towards each other, a destructive plate boundary is formed
Where are Volcanoes and earthquakes distributed
volcanoes and earthquakes mainly occur in narrow bands. When compared to the map above it is clear that the majority of the world’s earthquakes and volcanic eruptions occur along plate boundaries.
What is a constructive plate margin
Where two tectonic plates move apart below an ocean, the gap between them fills with molten magma, and the lava that is released constructs new crust. The Mid-Atlantic Ridge is the longest conservative plate margin in the world
What is a destructive plate margin
Destructive plate boundaries occur where dense, oceanic crust subduct lighter, continental crust forming a subduction zone. As the oceanic crust sinks below the continental crust, it melts, forming magma. Where magma rises to the surface, it forms explosive composite volcanoes.
Where are conservative plate boundaries found
Conservative plate boundaries occur where two tectonic plates are moving past each other, either in opposite directions or in the same direction but at different speeds. Plates do not slide past each other smoothly. Friction causes them to lock together.
