Geology year 8 Flashcards
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Geology definition
Geology is the study of Earth.
Inner core
Hot as surface of the Sun. It is solid. It is made of Iron and Nickel.
Outer core
Hot but not as hot as the inner core. It is made of liquid. It is composed of Iron and Nickel.
Mantle
It is hot. It is the largest layer. It is composed of various materials. It is solid and liquid.
Crust
It is cool. It is what we live on. It is composed of rocks and various materials. It is solid.
What are rocks made of?
Minerals
What are minerals made of?
They are made of chemicals and are the same substance throughout.
What are crystals?
Crystals are minerals inside of rocks that have a chance to grow into the shape they were meant to be. Rocks have different types of crystals depending on the way they’re formed.
Rock cycle
Sedimentary rock to Metamorphic rock = Changed by heat,pressure and/or chemical action. Metamorphic rock to magma = Melting. Magma to Igneous rock = Solidification. Igneous rock to Sedimentary rock = weathering and erosion. Metamorphic rock to Sedimentary rock = erosion. Igneous rock to Metamorphic rock = Changed by heat, pressure and/or chemical action.
Igneous rocks and the forming of extrusive and intrusive igneous rocks
Igneous rocks are to do with eruptions. When the magma is erupted out and reachers the Earth’s surface it becomes lava. When it is cooled and solidified it is called Extrusive igneous rocks. The magma that comes out cools inside the volcano/crust of the Earth and becomes rock with large crystals called intrusive igneous rocks. To recap, Igneous rocks is formed through the cooling and Solidification of magma or lava.
Characteristics of Extrusive rocks.
They have small crystals that may be hard to see. Extrusive rocks usually contain large spaces caused by gas bubbles making the rock look rough and bubbly.
Characteristics of Intrusive igneous rocks
They have large crystals. The large crystals interlock with each other.
Erosion
The removal of soil and rock by natural processes such as wind or water flow.
Sediment
A material that is broken down by processes of weathering and erosion.
Deposition
The process of a sediment being laid down and stopped to add to a landform or land mass.
Weathering
The deterioration of rocks, soils and minerals through contact with weather (wind, wind, sunlight etc).
Sedimentary rock formation
- Eroded sediments end up in the water and begin to settle (sedimentation).
- With time, more layers pile up and presses down the lower layers (compaction).
- More layers (strata) and further compaction forces out water from layers.
- Salt crystals glue the layers together (cementation). Rock mass formed is sedimentary.
Clastic sedimentary rocks
Weathering creates small rock fragments which are deposited (sink) in the sea and form a sediment, building up over time. Dead plants and animal can become trapped within the sediment forming fossils. Over time, the pressure of layers above compact the sediments together.
Examples of sedimentary rock
Breccia, conglomerate, sandstone and shale.
Chemical sedimentary rocks
They form when materials dissolved in water come out of solution, form a solid and sink to the bottom (evaporation and crystallisation). Examples: Halite, Gypsum, Limestone. Characteristics are that most have crystals, are quite soft and have no layering.
Organic sedimentary rocks
Form when dead plants and animal debris is buried under water and dirt. The exposure to high pressure and heat overtime turns the remains into organic rocks. The characteristics are that they can be layered, mostly soft and may contain fossils.
Timeline of how old fossils are
Fossils get older the deeper we dig. Paleozoic is 225 - 570 million years old. Proterozoic million is 570 million - 1 billion years old. Archeozoic is more than 1.5 billion years old.
How are Metamorphic rocks formed
It is formed from pressure and heat and it can be formed from any of 3 rocks.
Regional metamorphism
As tectonic plates move and collide on each other, they are heated and compressed. This is called regional metamorphism.
Contact metamorphism
When rocks come into contact with hot magma as it pushes through the crust, causing them to change.
Examples of metamorphic rocks
Slate, schist, phyllite and gneiss.
Characteristics of metamorphic rocks
They are dense and harder than sedimentary rocks. Often have crystals due to effect of heat and pressure. They have a zig-zag pattern.
Earth tectonic timeline
Permian Period was 250 million years ago and Earth was one large landmass. Alfred Wegener called this Pangaea. Next was the Triassic period which was 200 million years ago and the land was split into two: Lavrasia and Gonewanaland. Next was the Jarassic period which was 145 million years ago and the continents we knew today were starting to get visible. Next was the gretaceous period which was 65 million years ago. Lastly, there is the present day. Alfred Wegener thought of this theory.
Plate boundaries
The place where two tectonic plates meet
Divergent plate boundaries
When two plates are moving apart. Often occurs in the ocean. Molten rock (magma) rises up in the gap created. This is called shield volcanoes. A large eruption can occur where lava rises above ocean, where it cools and forms an island.
Convergent (subduction) plate bounderies
When the two plates move towards each other. Oceanic crust collides with continental crust. The oceanic crust is denser and is subducted into the Mantle and melts. Melted material mixes with volatile gases, which force it to surface = explosive eruption.
What may happen when two plates move into each other?
They can get jammed and pressure can build up. Eventually, the plates give way and jolt past each other and the energy is released as seismic waves and an earthquake occurs.
Convection currents
They are the hot air rising and cool air going down to be risen again which causes the plates to move.
Conservative boundaries
The plates slide past each other in vertically in different directions. No volcano occurs but earthquakes can be destructive. They are rubbing along each other.
Collision convergent boundaries
Two plates slowly move towards each other and when they collides they force up. It takes millions of years to do this. It is how mountain ranges like Himalayas are formed.
Physical weathering
Freeze-thaw weathering = When water gets into the rock and freezes which puts pressure on the rock and leaves a larger gap for more water to enter after the previous has melted and so on. Onion skin weathering = When it is very hot in the day and cold in the night so the rock contracts frequently until the surface is breaks/peels off.
Chemical weathering
Acid rain = When acid rainwater hits the rock. This is an extremely quick method of weathering.
Biological weathering
Plant roots can penetrate through even the strongest rocks over time. This causes the rocks to break. Animals walking over the rocks can also wear/weather the rocks off.
Deformation
Is the process by which rocks change shape when under stress.
Folding
Occurs when rock layers bend under stress. The bends are called folds.
2 types of folds
Syncline fold: youngest layers of rock arched downwards.
Anticline fold: the oldest layers of rock arched upwards.
Fault
A crack called a fault forms when large blocks of rock break and move past each other. This is due to so much stress on the rock. The blocks of rock on either side of a fault = fault blocks.
3 kinds of faults
Normal fault, reverse fault and strike-slip fault.
Normal fault
This is extensional stress. This is where the foot wall is above the hanging wall. The hanging wall is moving down as a result to gravity.
Reverse fault
The hanging wall is above the foot wall. This is compressional stress. This is common along convergent boundaries.
Strike-slip fault
This is shear stress. The fault blocks move past each other horizontally. These are common along transform boundaries.
How can one tell the difference between the hanging wall and the foot wall?
The hanging wall is the wall above the fault line. For example, is you see where the fault line is (which is where the area where one block is no longer touching the other near the bottom of the blocks) and you go up from it the hanging wall is the wall that the line crosses through.
Elastic deformation
Reversible strain
Deductible/plastic deformation
Is irreversible and keeps bent when released.
Fracture deformation
Material breaks and it is irreversible.
Orogeny
Mountain building process in the convergent plate.
Types of stress on a rock
Compression, tension, shearing and confining/uniform.
Examples and characteristics of igneous rocks
Examples of igneous rocks are Basalt, Granite, Obsidian and Pumice. Igneous rocks are hard and strong because the minerals and crystals they contain are hard and strong. They also have interlocking crystals which grow into each other and lock together.
