Schist rocks are metamorphic.
How did the theory of plate tectonics develop?
Around 1620 Francis Bacon made a discovery that the shape of South America and Africa looked as if they good have once been joint. In the 1800 Charles Lyle made a suggestion that the continents where very slowly moving however It was so slow that we could not see this.In 1850 Antonio Snider suggested that The Earth had once began to cool which made the continents split up due to a catastrophic event.In the 1900’s Alfred Wegener published a book which was about continental drift. Wegener believed that the continents where once joint together as they looked as If they were and also that the same fossil types had been found only down the side of south America and also Africa. Getting people to accept His theory was a problem:
1. He was not able to explain how the continental drift had happened.
2. His book was published in Germany during world war one so not that many people read it.
3. The book was not translated into English until 1924.
It was not until 50 years later after his ordinal idea, that the theory was accepted.
Alfred Wegener’s theory was finally accept due to :
In 1950 ocean floors were mapped, the mid Atlantic ridge was discovered and it was found out that the Atlantic ocean was getting wider by a few cm's per year.In the 1960’s Harry Hess made a suggestion that the ocean ridges were caused by convection currents in the earths mantle. Volcanoes occur along chains. Showing that the earth’s surface is split up into large plates. A final thing that helped his theory to be accepted was rgar Fred Viner and Drum matthews , found there were magnetic stripes on the ocean floor. This was the evidence that was needed for his theory to be at last accepted.
The plates were once together and then they slowly drifted apart.
The earth’s Crust
The Earth's crust is divided into huge, thick plates that drift atop the soft mantle. The plates are made of rock and are from 80 to 400 miles (50 to 250 km) thick. They move both horizontally and vertically. Over long periods of time, the plates also change in size as their margins are added to, crushed together, or pushed back into the Earth's mantle.
PLATE TECTONICS
The theory of plate tectonics was developed in the 1960's. This theory explains the movement of the Earth's plates (which has since been documented scientifically) and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation.
The top layers of the plates are called the crust. Oceanic crust (the crust under the oceans) is thinner and denser than continental crust. Crust is constantly being created and destroyed; oceanic crust is more active than continental crust.
TYPES OF PLATE MOVEMENT: Divergence, Convergence, and Lateral Slipping
At the boundaries of the plates, various deformations occur as the plates interact; they separate from one another (seafloor spreading), collide (forming mountain ranges), slip past one another (subduction zones, in which plates undergo destruction and remelting), and slip laterally.
Divergent Plate Movement: Seafloor Spreading
Seafloor spreading is the movement of two oceanic plates away from each other, which results in the formation of new oceanic crust (from magma that comes from within the Earth's mantle) along a a mid-ocean ridge. Where the oceanic plates are moving away from each other is called a zone of divergence
Convergent Plate Movement:
When two plates collide, some crust is destroyed in the impact and the plates become smaller. The results can change depending upon what types of plates are involved
Oceanic Plate and Continental Plate - When a thin, dense oceanic plate collides with a light, thick continental plate, the oceanic plate is forced under the continental plate; this is called subduction.
Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity.
Two Continental Plates - When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upwards.
Lateral Slipping Plate Movement:
When two plates move sideways against each other, there is a tremendous amount of friction which makes the movement jerky. The plates slip, then stick as the friction and pressure build up to high levels. When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake.
