Plate Tectonics Flashcards
What are the layers of the Earth?
Core, mantle, crust.
What is the structure, composition and consistency of the core?
There is a solid inner core and a semi-molten outer core, both of which contain iron and nickel.
What is the structure, composition and consistency of the mantle?
The part of the mantle nearest the core is quite rigid, the layer above this (the asthenosphere) is semi-molten and the very top of the mantle is rigid too. The mantle is made mostly of silicate rocks.
What is the structure of the crust?
There is oceanic and continental crust. Continental crust is 30-70km thick and less dense. Oceanic crust is 6-10km thick and more dense.
What is the lithosphere?
The lithosphere is rigid mantle and crust, which is divided into tectonic plates.
What is the asthenosphere?
The asthenosphere is the semi-molten mantle.
What is the plate tectonics theory?
In the 17th century, people first noticed that South America and Africa looked like they could fit together, there were suggestions that the continents may once have been joined. In 1912, Alfred Wegener proposed the theory of continental drift, suggesting that all the continents were once joined as one supercontinent called Pangea 300 million years ago. The North was called Laurasia, and the South was called Gondwanaland.
What did Alfred Wegener base his theory on, and why wasn’t it taken seriously initially?
Geological evidence and fossil records, but he couldn’t back it up with a mechanism that explained how the continents moved.
Explain why there are convection currents in the asthenosphere and how they move tectonic plates.
Radioactive decay in the mantle and the core generates heat. When lower parts of the asthenosphere heat up, they become less dense and slowly rise. As they move towards the top of the asthenosphere they cool down, become more dense, and slowly sink. These circular movements of semi-molten rock are called convection currents. Convection currents create drag on the base of the tectonic plates and this causes them to move.
What is the cause of sea floor spreading/how do tectonic plates move?
Convection currents in the asthenosphere.
Explain the process of sea floor spreading.
Rising convection currents diverge at the base of the lithosphere, the drag of the convection currents causes the oceanic plates above them to diverge too. Magma rises up to fill the gap created, then cools to form new crust. Over time, the new crust is dragged apart and more new crust forms in-between.
What are the 5 pieces of evidence for the theory?
Geology, fossil records, living species, climatology and paleomagnetism.
How does geological evidence support the theory?
Areas of South America and Africa have rocks of the same age and composition, which line up when you fit the contents together. These rocks must have formed under the same conditions and in the same place in order to match so well.
How do fossil records support of the theory?
By fitting land masses together you can match up the distribution of some fossils (e.g. fossils of the mesosaurus). It is very unlikely that this species migrated over thousands of miles of water, or that they evolved in different places.
How do living species support the theory?
The same living organisms can be found on different continents (e.g. earthworms of the family megascolecidae are found in New Zealand, Asia and North America. It is very unlikely that this species migrated over thousands of miles of water, or that they evolved in different places.
Hoes does climatology support the theory?
There’s evidence that the past climates of some continents were similar, despite being thousands of miles apart now. Large coal deposits that were formed in tropical conditions have been found in North America and parts of Europe, suggesting these regions were once closer to the equator than they are now.
How does palaeomagnetism support the theory?
Once every 200,000 years, the Earth’s magnetic field reverses polarity. As magma erupts from mid-ocean ridges, magnetic materials in the molten rock align themselves with the direction of the Earth’s magnetic field. When the crust has solidified, the alignment is fixed. The magnetic minerals in crust created in times of normal polarity are aligned in the opposite direction to those in crust created in periods of reverse polarity. This creates a series of alternating magnetic stripes along the sea floor. The stripes show that the crust is older the further away from a mid-ocean ridge you go, this means the plates are moving apart.
What is the evidence for sea floor spreading?
Palaeomagnetism.
What is the evidence for convection currents?
Continental drift.
Which hazards occur at constructive margins?
Earthquakes and volcanoes.
Which hazards occur at oceanic-continental destructive margins?
Earthquakes and volcanoes.
Which hazards occur at conservative margins?
Earthquakes.
In which direction do plates move at constructive margins?
Apart.
In which direction do plates move at destructive margins?
Towards each other.
In which direction do plates move at conservative margins?
Past each other.
What landforms are created at constructive margins?
Mid-ocean ridges and rift valleys.
How are mid-ocean ridges formed at constructive margins?
Where plates diverge beneath ocean, rising magma causes the oceanic crust to bulge and fracture, forming fault lines. As the plates keep moving apart, the crust between parallel faults drops down to form a rift valley. For example, the Mid-Atlantic Ridge.
How are rift valleys formed at constructive margins?
Where plates diverge beneath land, rising magma causes the continental crust to bulge and fracture, forming fault lines. As the plates keep moving apart, the crust between parallel faults drops down to form a rift valley. For example, the East African Rift System.
How are volcanoes formed at constructive margins?
The mantle is under pressure from the plates above. When they move apart, the pressure is released at the margin. The release of pressure causes the mantle to melt, producing magma. The magma is less dene than the plate above, so it rises and can erupt to form a volcano.
How do earthquakes happen at constructive margins?
The plates don’t move apart in a uniform way, some parts move faster than others. This causes pressure to build up. When the pressure becomes too much, the plate cracks , making a fault line and causing an earthquake.
What landforms are created at oceanic-continental destructive margins?
Deep sea trenches and fold mountains.
How are deep sea trenches formed at destructive margins?
The more dense oceanic crust is subducted under the less dense continental one (or less dense oceanic one), forming a deep sea trench. For example, the Peru-Chile trench.
