Unit 1C - The Restless Earth Flashcards
What are the three basic rock groups?
Igneous
Sedimentary
Metamorphic
Give two examples of igneous rock types.
Basalt
Granite
Give two examples of sedimentary rock types.
Sandstone
Limestone
Give two examples of metamorphic rock types
Marble
Slate
Explain how igneous rocks formed, making sure to describe their general appearance and structure.
Explain why the formation of a crystalline structure in the rock may not occur.
Igneous rocks are those that have been formed by the cooling and solidifying of molten rock (magma) from underneath the Earth’s crust. 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 the crystals (for example, basalt). If the magma is cooled slowly underground, then a crystalline structure will be more evident (for example, granite).
Explain how sedimentary rocks are formed, making sure to describe their general appearance and structure.
Sedimentary rocks are those that have been formed by the sediments that have built up over a long period of time, usually under water. The sediments are made up of weathered and eroded material that builds up in layers. As more and more material is added, pressure pushes air and water out, and the sediment gets cemented into a rock.
The mineral particles in the rock are usually made from mud, sand and clay. Limestone and sandstone are good examples of sedimentary rocks. These rocks can contain fossils. Sedimentary rocks are very easy to recognise due to their flat structure in stratified beds.
(Please see diagram of stratified layers of rock on page 107 of textbook)
Explain how metamorphic rocks are formed, making sure to describe their general appearance and structure.
Metamorphic rocks are those rocks that have been changed from an earlier state through the addition of pressure or heat. The rocks would originally have been igneous or sedimentary. For example, marble is a metamorphic rock which was once limestone, a sedimentary rock.
Metamorphic rocks are tough and can be highly resistant to erosion, as they have undergone very hard conditions in their formation. They are often used as building materials, for example slate.
How is basalt formed?
Lava erupts from volcanoes and solidifies.
How is granite formed?
Magma hardens within the Earth’s crust.
How is sandstone formed?
Particles the size of grains of sand are pressed together.
How is limestone formed?
Shells and skeletons of tiny creatures on the sea floor are compressed.
How is marble formed?
Limestone is altered by heat or pressure.
How is slate formed?
Shale, clay and volcanic ash is changed through pressure.
Describe the structure of the Earth.
Crust
Mantle
Outer core
Inner core
What is the temperature of the Earth’s core?
Over 6,000 °C
What is the core composed of?
Iron and Nickel
What is the state of the inner core and outer core?
Inner core = Solid
Outer core = Liquid
What is the mantle?
The mantle is the thickest layer of the Earth, containing molten rock which flows and moves about.
What is the mantle composed of?
Silicate rocks
What is the temperature of the mantle?
3,500 °C
What are the mantle layers also known as?
The asthenosphere
What is the crust?
The crust is the outermost section of the Earth. It is a thin layer, varying in depth in different places. The crust is broken up into several pieces, which are known as plates.
The crust and some of the more solid mantle are sometimes known as…
The lithosphere
What are plates?
Sections of crustal rock.
Who originally proposed the theory of plate tectonics?
Alfred Wegener
What was the name of the original supercontinent?
Pangea
How do convection currents cause plate movement?
Deep inside the thick mantle layer of the Earth, the extreme heat from the Earth’s core causes mantle rock to melt. As the rock becomes liquid, it becomes less dense than the material above it and starts to rise towards the surface. The molten rock (magma) rises and attempts to break through cracks in the crust where possible. The magma in the mantle layer will then interact with the crust (often due to friction from the moving mantle rock) causing sections of the crust to move towards or away from each other. Any excess magma, now that it is far away from its source of heat, will start to cool and solidify, and as the rock becomes more dense, the rock will sink back deeper into the deeper into the mantle, where it will become heated again.
What are the two different types of plate that make up the Earth’s crust?
Continental plates
Oceanic plates
What are continental plates?
Continental plates are usually thick plates that form at land masses/continental areas.
What are oceanic plates?
Oceanic plates are usually thinner plates that form at the bottom of ocean floors.
What are the features of continental plates, giving an example of the rock types that they are composed of.
- 35-100 km (thick)
- Rocks can be very old
- Generally contains ‘light’ rocks that are less dense
- Example: Granite
What are the features of oceanic plates, giving an example of the rock types that they are composed of.
- 6-10 km (thin)
- Rocks can be very young
- Generally contains ‘heavy’ rocks that are more dense
- Example: Basalt
What are the processes and landforms associated with constructive plate margins.
A constructive plate margin is a boundary where two plates are moving away from each other. They are moved as the convection currents push the plates further away.
Landform: Mid-ocean ridge (a gap in the seabed)
Example: Iceland
Constructive plate margins can only occur …
Under the oceans