Tectonic plates & Earth Flashcards
What is the continental drift theory?
Alfred Wegner believed that all the continents we know of today were all connected to form one supercontinent called Pangea.
The reason he believed this is because he found evidence of plant and animal fossils spread across each continent.
Evidence from modern continents: Mountain ranges in South America and Africa line up.
European coal fields match with similar coal fields in North America.
Evidence from Fossils: Fossils of the plant and trees found in rocks on widely separated landmasses.
Evidence from dinosaurs: Fossils of tropical plants found near Arctic Ocean.
Scratches in rocks made by dinosaurs found in South Africa.
Other scientists didn’t believe him because he didn’t have a reason as to how the continents actually drifted apart.
What are the two types of crust?
Oceanic crust is usually about 5–10 km thick and is mostly made up of basalt, a dense volcanic rock.
Continental crust is usually between 20–70 km thick and is lighter than oceanic crust.
What is the Earths structure like?
Crust: A layer of solid rock, 5-70km thick it is the thickest under the continents.
Mantle: The thickest of the four layers, made of solid and partially melted rock.
Outer core: A liquid mixture of iron and nickel. Its flow generates the Earths magnetic field.
Inner core: A solid mixture of iron and nickel at extreme pressures and temperatures (over 6000 degrees).
What are divergent plate movements?
When new divergent boundary forms on a continent
called a RIFT or CONTINENTAL RIFT. This plate movement is “Spreading centre - Slow”.
When a divergent boundary forms under the ocean its
called an OCEAN RIDGE. This plate movement is “Spreading centre - Fast”.
Divergent (constructive) two plates move away from each other. Molten rock (magma) rises from the mantle to fill the gap between two plates. This causes volcanoes and earthquakes but also forms mid-ocean ridges that develop into islands.
What are transform boundaries or plate movements?
Causes earthquakes, which can be fairly violent and frequent.
Two plates slide past each other, without creating or destroying any land.
As they move past each other they often get stuck, building up great pressure until finally they jolt past each other. This sudden movement is what causes earthquakes.
What are convergent plate movements?
A convergent (destructive) plate boundary is where two plates push against each other causing violent earthquakes, volcanoes and mountain ranges to be formed.
When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.
The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.
The worlds deepest parts of the ocean are found along trenches.
Continental plates (thick but not dense) push against oceanic plates (thin but dense) The plate with the older (cooler, more dense) crust descends into the subduction zone. Subduction is when oceanic crust sinks underneath continental crust .A chain of volcanoes forms on the overriding plate.
Continent on Continent; Neither side of the boundary wants to sink beneath the other side
As a result the two plates push against each other
Crust - buckles and cracks
High mountain ranges are pushed up.
What is seafloor spreading?
Two oceanic plates move away from each resulting in the formation of new oceanic crust.
Convection currents in mantle rise under oceanic ridges and spread. Oceanic crust (basaltic) created at ridges. Crust plus upper mantle (lithosphere) move laterally away – going along for the ride.
Evidence from molten material (magma)
Evidence from magnetic stripes
Evidence from drilling samples
What are convection currents?
Convection is a process of heat energy transfer; it occurs in matter where particles flow freely, such as liquids and gases. Convection produces currents within fluids, which distributes or transfers heat energy from one place to another. These convection currents can be found in a range of places in nature. Large-scale convection currents can also be described in Earth’s mantle.
Density is defined as the mass per unit volume. Density is referring to the amount of matter within a given volume of a substance. The more particles packed together in a given volume, the greater the density of that substance will be.
The particle model can be used to explain how a cold liquid has a higher density than a hot liquid of the same substance. This also applies to gases. This is a result of the difference in energy content of the liquid or gas.
NOTE: in the same substance the mass of the particles will be the same. The less energy a liquid has, the more tightly packed the particles. As a liquid heats up, more energy is being transferred to the particles. Thus they move more, become less bunched and produce more space between them, thereby becoming less dense.
Why do volcanoes erupt?
Heat deep within the Earth’s Mantle melts rocks to create a slow moving substance called Magma.
Magma is lighter than solid rock so it rises and collects in magma chambers.
Eventually magma pushes through vents in the Earth’s surface causing a volcanic eruption.
Volcanoes form along plate boundaries called subduction zones.
Volcanoes are most common along the ring of fire where there are many plates subducting.
Why do earthquakes happen?
Convergent transform plate boundaries cause earthquakes the most severe ones.
Earthquakes are vibrations caused by earth movements at plate margins and at major fault lines (cracks in the earth’s surface).
The two plates at a plate margin cannot move past each other easily.
The two plates lock together. Friction causes pressure to build up.
Suddenly the pressure is released and the plates jolt into a new position.
This causes seismic waves. The vibration are called an Earthquake.
Fault: A fracture in the rock that makes up the Earth’s crust.
Epicentre: The point at the Earth’s surfaces directly above the focus.
Focus: The point within the Earth where an earthquake rupture starts.
Platea: Massive rocks that make up the outer layer of the Earth’s surface and whose movement along faults trigger Earthquakes.
Seismic Waves: Waves that transmit energy released by an Earthquake.
What are P and S waves?
P stands for primary waves.
They are longitudinal waves.
They can pass through solids and liquids.
They cause the ground to move right to left.
S stands for secondary waves. They cause the ground to move up and down. They are transverse waves. They only pass through solids. They are slower than P waves.
Where do trenches, rift valleys, rifts and mid ocean ridges form?
Mid Ocean Ridge: Diverging plant boundaries on oceanic crust.
Trenches: Converging plate boundaries at the edge of subduction zones.
Rifts and Rift valleys: Diverging plate boundaries where the two boundaries move apart.
Where is the ring of Fire?
Around the Pacific Ocean some continents are Japan and the Phillipines.
