Science - Plate Tectonics Flashcards
Alfred (Wegner) Wagwan G’s 2 pieces of evidence for Continental Drift
- The continents fit together like a jigsaw.
- There are fossils of the same species on diferent continents.
Harry Hess’ 3 pieces of evidence for Seafloor Spreading
- Magnetic striping
- The seafloor further from the ridges is older than the rock closer to the ridges
- There is less sediment ontop of the crust that is close to the ridges compared to the crust that is far from the ridges
Magnetic Striping
When the magnetite in the magma aligns with the earth’s magnetic field which changes every few hundred thousand years, causing the magnetite to point in an opposite direction. This creates stripes of rock with the magnetite pointed one way, and stripes of rock with the magnetite pointed the other way.
What is a Diverging Boundary?
Where the plates move away from each other, creating new crust.
What is a Converging Boundary?
When the plates move towards each other, destroying crust.
What is a Transform Boundary?
When the plates move past each other.
Subduction
When a plate goes underneath another plate in a converging bourndary.
Characteristics of oceanic crust
- Denser
- Thinner
- Contains heavier elements (Fe, Mg, etc.)
- It is wet and slippery as well as containing lots of sealife due to being underwater
Characteristics of continental crust
- Less dense
- Thicker
- Contains lighter elements (Al, Si, etc.)
- It is dry and desert like, containing humans, civiliazations as well as mostly of the known animal species.
Theories for plate movement
- Convection currents
- Gravity
Convection currents
When the hot magma rises from the asthenosphere, hitting the plates and drags them before sinking back down
How does gravity make plates move?
Either:
1. Slab pull, where gravity pushes on the crust near the subduction zone
or:
2. Ridge push, where the new crust that formed at the ridge pushes older crust down.
Seafloor spreading
A theory where new rock is formed at mid-ocean ridges and slowly moves outwards.
Tectonic plates
Massive slabs of rock that make up the earths crust.
Lithosphere
The highest layer of earth made of the crust and upper mantle. This layer is rigid.
Asthenosphere
The second layer of earth made of lower mantle. This layer is flexible.
The outer core of the earth
The second deepest layer of the earth made of liquid metal
Rifting
A process to split a continent into two where a continent would crack and fill with water from the oceans, folowed by seafloor spreading.
Landform made by continental-continental converging boundaries
Mountain ranges
Landform made by oceanic-continental converging boundaries
Mountains, volcanoes and trenches
Landform made by oceanic-oceanic converging boundaries
Island Arcs, Volcanoes
Landforms made by transfom boundaries
Mountains, Fault lines
Landforms made by divergent boundaries
Rift valleys, Ocean ridges and Volcanoes
What are 4 things that volcanoes release when erupting?
- Ash
- Lava
- Gas (Steam & Hydrogen sulfate)
- Scoria (Solid volcanic rock)
Why did the scientific community initially reject Wegener’s theory?
He couldn’t explain how the continents moved
Magma vs Lava
Magma is undergorund while Lava is aboveground
Hot spot volcanoes
Isolated weak spots within a plate where a lot of magma is present. When the magma floats to the surface it creates a hot spot volcano.
How do earthquakes occur?
When tectonic plates that are held together with friction eventually slip, releasing energy into the surrounding rock or water.
How are earthquakes measured?
Using a seismometer
Primary waves
Waves from an earthquake that move back and forth. They travel the fastest out of the three waves.
Secondary waves
Waves from an earthquake that move up and down. They travel at speeds between Primary and Surface waves
Surface waves
Waves from an earthquake that travel in a rolling motion. They travel the slowest and are the most destructive.
Where do earthquakes occur
Most commonly on plate boundaries, especially on transform boundaries.
Focus
Where the slip occurs in an earthquake
Epicentre
The point on the suface above the Focus
When does a tsunami occur?
When an earthquake occurs in the ocean
Ritcher scale
A logarithmic scale for earthquake severity
Magma moves through ____ in the earths crust
Weaknesses
