Please enable JavaScript.
Coggle requires JavaScript to display documents.
Earth Science (10.1 Moving continents (Magnetic striping (Geologists found…
Earth Science
10.1 Moving continents
-
-
-
Magnetic striping
Geologists found that as they went away from the ridge, the magnetic field preserved in the rocks kept changing. At the start, the rocks had north pointing in the correct direction (towards what is now Earth’s north pole). Suddenly the direction of north changed to the opposite direction. North became south, then changed back again. This indicated that over millions of years Earths magnetic field changed
These patterns of strips of rocks with alternating magnetism are called magnetic striping. The patterns on either side of the ridge are symmetrical—rocks at a particular distance from the ridge on one side always have their magnetic fields pointing in the same direction as rocks the same distance away on the other side.
In the 1950s, scientists discovered that many rocks contained the magnetic iron oxide mineral called magnetite. Magnetite has a north-seeking pole and a south-seeking pole, just like a compass needle.When molten rock solidifies, all the magnetite particles in it line up with Earth’s magnetic field to point in the same direction. In this way, the direction of Earth’s magnetic field at the time is preserved in the rock.
More research into magnetic striping led geologists to support Hess’s theory about seafloor spreading. They concluded that there were great cracks in the crust and that magma rose up and added to each side of a crack to form new crust on the sea floor. New sea floor was being added equally on each side of the ridge.
This is why 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 many millions of years, so did the magnetic direction preserved in the rocks
-
Tectonic Plates
Tectonic plates can be very large. For example, the whole of Australia and parts of New Zealand are on a single tectonic plate. Most of the crust under the Pacific Ocean is on another plate. There are seven extremely large tectonic plates that are bigger than most continents. There are another ten or so medium-sized ones and about 60 smaller plates.
The crust is rigid, inflexible and is split into many large sections that move about on Earth’s surface. Each section is known as a tectonic plate.
-
-
10.? Tsunamis, their locations and warning systems
Tsunamis are caused by earthquakes which epicentres are in the ocean, the waves sent out from the earthquake form a massive wave
Usually begin around plate boundaries, but can travel for kilometers away from the epicenter or plate boundaries
Australia created an early warning system for tsunamis. This system uses data from 50 seismic stations in Australia and 120 from overseas stations. Computers linked to these stations alert scientists to a potential tsunami. Scientists then input the data into a scientific model to determine how big the tsunami may be, how long it may take to reach Australia and where it could hit the coast. They check with deep ocean detector buoys to see if the tsunami actually forms and if it is acting as expected from the model.
Recorder on seabed monitors changes in pressure; it can detect tsunamis as small as one centimetre. An acoustic link transmits data to moored surface buoy. Data relayed to satellit. Satellite transmitsdata to ground station
10.2 Plate Movements
Mountain building
When two continental plates collide, both are pushed upwards because both have similar densities. This upwards push forms ranges of very high mountains.
If oceanic crust is colliding with continental crust, then the denser oceanic plate sinks under the lighter continental plate. The continental plate becomes distorted, forming fold mountains and volcanoes. Fold mountains form when plates collide and the crust crumples upwards.
-