The Restless Earth Flashcards
Core
At the earths core, the temperature will be over 6000 degrees C. It is believed to be made out of iron and nickel, with a liquid core surrounding a solid inner core. The outer core is about 1200km deep and the inner core around 2200km deep.
Mantle
This is the thickest layer (2900km) it is made of silicate rocks that remain molten in the high temperatures (3500 degrees C) and flow it move about. These layers can be known as asthenosphere.
Crust
This is a thin layer (5 to 7km deep). The crust and some of the more solid mantle are sometimes known as the lithosphere.
How do convection currents cause plate movement
Convection currents occur in the mantle. These currents are caused by radioactivity decay in the core. The extreme heats this creates caused the mantle rock to melt. As rock becomes liquid, it becomes less dense than the material above it and starts to rise to the surface. This movement causes the plates to move towards or away from the heat source (core) so it becomes more dense and sinks back deeper into the mantle where it will become heated again.
Continental plates
Thick plates (35-100km) that form from land masses/ continental areas.
Ocean plates
Usually thinner plated (6-10km) that form at the bottom of ocean floors.
Constructive plate margin
Plates pull apart by the convection currents in the soft rock. Magma rises between them forming small volcanoes on the ocean floor it hardens to basalt, Which form new ocean floor so the ocean floor is spreading about 2.5 cm per year. Landform: mid-ocean ridge.
Example of a constructive plate margin
Mid Atlantic ridge Iceland.
Deconstructive plate margin
The nasca plate is heavier (oceanic crust is heavier) so it gets pushed down at an ocean trench (subdued- pushed down).
The rock jolts and grinds its way down, causing earthquakes. At the same time, it heats up. Some rock melts its way through the Andes to form a volcano.
Landform: subduction zone, ocean trench.
Example of a destructive plate margin
Nevado del ruiz, Columbia.
Collision plate margin
The crust gets pushed and folded upwards to form a mountain range. The mountain of the rock causes earthquake. But no rock gets pushed down and melted, so no volcanos.
Fold mountains.
Example of collision plate margin
Himalayan mountains.
Conservative plate margin
Parts of the plates get stuck, they lurch free. This causes earthquakes. But no rock get pushed down & melted, so no volcanos. Landform: fault lines.
Example of conservative plate margin
San andreas fault, California.
Earthquake definition
A term or starting in the crust which causes the shaking to be felt in the earths surface.
Volcano definition
A cone shaped mountain built up from hardened ash and lava, from which molten material erupts onto the earths surface.
Subduction zone
An area where crust is being forced down into the mantle.
Mid- ocean ridge definition
Where two plates made of oceanic crust move apart, the magma of the mantle rises to fill the gap, causing the crust to rise and form a ridge.
Fold mountains definitions
When the crust of a continental plate folds and buckles upwards.
Ocean trench definition
When oceanic crust is forced down (subducted) into the mantle and sinks below normal level to create a deep trench in the ocean.
Fault line definition
A weak line in earths surface, where crust is moving, causing earthquake activity.
Examples of igneous rocks
Basalt & granite.
Examples of sedimentary rocks
Limestone & sandstone.
Examples of metamorphic rocks
Slate & marble.
How are igneous rocks formed
Formed from cooling and solidifying of magma. Molten rock is called lava on the surface. Extrusive - on the surface crystals are usually evident in the rock. However, if the rock cools quickly as the lava hardens on the surface there will be little evidence of crystals (basalt) if the magma is cooled slowly underground then crystals are more evident (granite)
