Plate tectonics Flashcards
Geology
study of the Earth’s structure, the rocks it is composed of and the processes by which it changes.
Found in?
- position of continents
- types of lifeforms
- climates must be collected from a broad range of sources around the globe.
- landforms, rocks, minerals and fossils
Static Earth Theory
Earth’s continents have changed significantly since it was formed.
Catastrophism
idea that violent geological upheavals, such as volcanoes and floods, were the main driving force for past change on Earth.
Uniformitarianism
geological processes happening today have been the same throughout Earth’s’ history.
“The present is the key to the past”
Charles Lyell
helped build the geologic time scale.
based on the law of superposition, which states that younger layers of sediments rest on top of older layers
Alfred Wegener
Proposed the theory of continental drift.
Earth’s continents move across the ocean over time.
the continents were once all joined together in a supercontinent he called Pangaea.
Plate tectonics
Plate tectonics theory has replaced the theory of continental drift.
the Earth’s crust consists of giant pieces called tectonic plates. Movement occurs because of convection currents in the molten magma under the plates.
Layers of The Earth
Crust: outermost layer of rock
Mantle
-Asthenosphere: mobile upper mantle
-Mesosphere: rigid lower layer
Outer core: liquid nickel and iron
Inner core: solid ball of iron
Convection in the Mantle
Hotter, less dense material in the lower mantle moves upward, while cooler, more dense material in the upper mantle moves downward.
This process is called convection.
It is the main driving force for the movement of tectonic plates.
Evidence - Earthquakes
The location of earthquakes reveal boundaries between tectonic plates.
Earthquakes can occur when plates collide or slide past each other.
Evidence - Volcanoes
When a more dense tectonic plate collides with a less dense tectonic plate, the more dense plate is forced down (subducted) into the mantle.
This can cause volcanoes to form.
Evidence - Ocean Floor Spreading
Oceanic tectonic plates can spread, forming mid-ocean ridges.
Pressure from mantle convection pushes the plates apart.
Mid-ocean ridges are located along the boundaries of tectonic plates.
Evidence - Paleomagnetism
particles containing iron, cobalt or nickel can align with Earth’s magnetic field.
These rocks show that Earth’s magnetic field direction has reversed many times in the past.
Cause of Earthquakes
caused by the sudden movement of tectonic plates that make up Earth’s crust.
The point within Earth where tectonic plates move against each other is called a fault. Earthquakes are more likely to occur along faults than other locations.
Earthquake Focus and Epicentre
When a tectonic plate moves, energy is transmitted in all directions as seismic waves.
The focus is the location within the Earth where energy is released. The focus is the source of the seismic waves.The location on Earth’s surface directly above an earthquake focus is called the epicenter.
Body waves
move through Earth’s interior.
Primary waves (P)
Arrive from focus first, travel fastest, longitudinal waves. This means that the direction of vibration is parallel to the direction the wave travels. through solids and liquids. Pass through the liquid part of the core, but waves refract (bend) as they pass from one layer to another.
Determines the location and properties of Earth’s interior layers.
Seconadary waves (S)
Arrives second. Transverse waves which means that the direction of vibration is perpendicular to the direction the wave travels. Travel through solids, but not through liquids. There is an S wave shadow on the side of Earth opposite to a source of seismic waves. Earth’s outer core is liquid.
Body waves
move through Earth’s interior.
Surface waves
Just below or along the Earth’s surface. They travel slower and not as far as body waves. Surface waves are especially damaging to buildings.
Love (L) waves
side-to-side motion.
Raleigh (R) waves
rolling motion (like an ocean wave).
seismometer
an instrument that detects and records seismic waves.
Order of waves
P waves arrive first, then S waves and then finally L and R waves. The average speeds of these waves are known. After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.
Measuring Seismic Waves: Location
Triangulation: Three seismograph stations are needed to locate the epicenter of an earthquake.
Measuring Seismic Waves: Amplitude
The amplitude of a wave is the maximum displacement that occurs during the vibration. The maximum wave amplitude is used to calculate the earthquake’s magnitude.
Richter Scale
one of the scales used to describe the magnitude of earthquakes.
Earthquake predictions?
foreshocks, changes in magnetic fields, changes in groundwater levels and patterns in past earthquakes have helped to predict earthquakes.
