SCIENCE EARTH SCIENCE TEST Flashcards
Wegner Theory
Alfred Wegener proposed that the continents were once united into a single supercontinent named Pangaea. He suggested that Pangaea broke up long ago and that the continents then moved to their current positions. He called his hypothesis continental drift.
Sea-Floor Spreading
The process of new crust forming at the ocean ridges and spreading outwards
The major tectonic plates
African plate
Pacific plate
Australian plate
Antarctica plate
Eurasian plate
Antarctic plate
North American plate
South American plate
Hess’ Theory
50 years after Wegener proposed his theory, Harry Hess confirmed the theory by using the evidence of seafloor spreading to explain what moved continents.
Magnetic Stripping
Magnetic striping: the patterns of magnetism trapped in rocks on each side of plate boundaries. When molten rock solidifies, all its magnetic particles line up with Earth’s magnetic field to point in the same
direction. The pattern of magnetism was symmetrical – the rocks at equal distances on each side of the ridge were formed at the same time and so had their magnetic fields pointing in the same direction. As Earth’s magnetic field changed over millions of years, so did the magnetic direction preserved in the rocks
Age of the Sea-floor
The further the rocks of the Sea-floor were from the ridges, the older they were. The Sea-floor as very young compared with the rocks in the continents.
Sediment Thickness
The sediment rock layers on the ocean floor become thicker as you move away from the ridges. This means that sediments had been falling for longer on the rocks on the sea floor further away from the ridges
Convection Currents
Convection currents drive the movement of Earth’s rigid tectonic plates in the planet’s fluid molten mantle. In places where convection currents rise up toward the crust’s surface, tectonic plates move away from each other (Sea-floor spreading).
Two Types of Crust
Oceanic Crust
Continental Crust
Oceanic Crust
It is found on the ocean floor, below sea level. The oceanic crust is thinner, and denser than the continental crust due to the presence of iron and magnesium.
Continental Crust
It is the crust that forms the continents. Contains lighter elements such as aluminium and silicon.
Volcano
Is a place where extremely hot material from inside Earth erupts at Earth’s surface. Materials can include:
Gas (Steam and hydrogen sulfide)
Ash
Lava
Lumps of solid volcanic rock such as scoria
Earthquake
An earthquake is the rapid movement of the ground, usually back and forth and up and down in a wave motion. Caused by the rapid release of energy as the tectonic plates move.
Detecting Earthquakes
Earthquakes are detected by using an insturment called a seismometer.
Seismic Waves
The movement of the ground in an earthquake occurs in a shaking back and forth motion called a wave. These waves are known as called seismic waves. There are three main types of seismic waves.
Primary Wave
Longitudinal waves that travel fast through the earth. Longitudinal waves move the ground back and forth.
Primary Wave
Longitudinal waves that travel fast through the earth. Longitudinal waves move the ground back and forth.
Secondary Waves
Are transverse waves that travel slightly slower than primary waves through Earth. Transverse waves move the ground up and down.
Surface Waves
Are the slowest waves and cause the most destruction.
Crust
The crust is the Earth’s outermost solid layer. It makes up our mountains and plains and makes up the floors of our ocean and seas. The crust varies in thickness from about 5km under the oceans to about 30km under the continents. The crust is split into sections known as tectonic plates.
Rifting
Rifting is the process of continents breaking up, subsiding and allowing in water from the sea.
Divergent Plate Boundaries
Where plates are moving away from each other in opposite directions. Aalso known as constructive boundaries. When the plates separate they leave a rift between them. The mid-ocean ridge forms a diverging boundary the ridge is the evidence that new curst is being constructed. Diverging boundaries also occur on land.
Converging Boundaries
Where plates are colliding with each other. They are also known as destructive boundaries. Rock is destroyed at converging boundaries. These collisions make all sorts of land features such as mountains, chains of island and underwater trenches.
Transform Boundaries
*Where plates are sliding parallel to each other but in opposite directions.
Subduction
When one plate sinks below another plate during a collision.
GPlates
A tectonic reconstruction software, which helps us visualiser the earthe’s crust.
Three ways GPlates help us
-Opal Prospectors use GPlates to find opal fields
-Scientists use GPlates in their research.
-Helps us predict the changes on the Earth’s surface in the future.
Volcanoes and plate boundaries
Most volcanoes are found at or near plate boundaries. This is because the movement of the plates create weakness in the crust and also generates intense heat that can melt rock.
Earthquakes and plate boundaries
Most earthquakes start at the edge of a tectonic plate.
