1) Plate tectonics theory ( mostly complete)

1) Plate tectonics theory ( mostly complete)

1. Earths structure

   • The Earths Core
     • At the centre of the Earth is the Core. The core is split into an inner core and outer core. the core itself is 5100km- 6378km deep
     • Inner core is a solid ball 5100 km containing lots of Iron and Nickel
     • Outer core is Semi- Molten and also contains lots of Iron and Nickel 6378 km
   • The Earths Mantle
     • The Part of the mantle nearest the core is quite rigid
     • The Layer above is called the Asthenosphere. It is Semi Molten
   • The Earths Crust
     • The Outer layer of the earth is the crust. the rigid top part of the mantle and crust is called the lithosphere

2. The Ground underneath the surface is moving all the time.

3. Tectonic plates and movement

   • the lithosphere is divided into lots of slabs called tectonic plates. the plates are moving due to convection currents as in the Asthenosphere. the places where plates meet are called boundaries or plate margins

4. plates moving apart

   • Crust is created when plates move apart.
     • Rising convection currents diverge (move apart) at the base of the lithosphere. The drag of the convection currents causes the plates to move above them and diverge too.
     • Magma rises up to fill the gap created then cools to form new crust. Over time, the new crust is dragged apart and even more new crust forms between it. when this happens at a plate margin under the sea, the sea floor gets wider. (sea floor spreading) This creates structures called mid-ocean ridges (ridges of higher terrain on either side of the margin
     • A similar process of spreading occurs on land margins where plates are moving apart. when plates move together, sometimes, the crust is destroyed. sometimes, it can also be pushed up into mountains.

5. Alfred Wengener

   • in 1912, Alfred Wegener proposed the theory of continental drift. he suggested that all continents were once joined as one supercontinent called Pangea which drifted apart.
   • Wegener based his theory on Geological evidence and fossil records but couldn't back it up with a mechanism that explained how the continents moved. However, in the 1950s, palaeomagnetism provided evidence of continental drift. then in the 1960s. Sea floor spreading was discovered. this provided a mechanism,
     • The continental drift theory was developed further by scientists after these findings. It grew into the theory of plate tectonics.
   • evidence
     • Geology
       • Areas if South America and Africa have rocks od the same age and composition. If you fit these continents together, the distribution of the rocks matches up. you can also match up the same rock type and distribution of some mountain ranges. e.g mountains in Norway, Sweden and Finland are smilar to those on the east coast of North America.
       • These rocks and mountains must have formed under the same conditions and in the same place in order to match so well. this would only be possible if all continents were once joined.
     • Fossil records
       • By fitting land masses together, you can match up the distribution of some fossils. It's very unlikely that these species migrated across thousands of miles of water or that they evolved in different places. So fossil records suggest that these places were joined together when these organisms were alive hundreds of millions of years ago.
         • examples of species
           • reptile
             • Lystosaurus
             • Cynognathus
             • Memosaraus
           • plant
             • Glossopteris
     • Living Species
       • The same living organisms can be found on different continents- like the fossilised organisms. it is unlikely that they migrated across oceans or evolved in different locations.
         • e.g Earthworms of the family of Megascolecidae are found in New Zealand, parts of Asia and Noth America. This suggests that the continents were once joined, allowing the Earthworms to travel between them.
     • Palaeomagnatism
       • Palaeomagnetism is the study of the history of the Earths magnetic field. Once every 200,000 years or so, the Earths magnetic field reverses polarity (the magnetic North and south poles switch). palaeomagnetism has provided evidence for the process of sea floor spreading
       • As Magma erupts from the mid-oceanic ridges, magnetic minerals in the molten rock align themselves with the direction of the Earths magnetic field. when the new crust has solidified, the alignment is fixed.
       • The magnetic minerals in the Crust created in periods of normal polarity (magnetic North near the North pole) are aligned in the opposite direction to those in the crust created in periods of reverse polarity (magnetic North near south pole)
     • Climatology
       • There's evidence that the past climates of some continents were similar despite being thousands of miles apart now. this suggests that they were located together and in a different place on earth to where they are now.
         • Similar glacial deposits are found in Antartica, Africa, South America, India and Australia. By fitting these places together, they match the distribution of deposits which suggests they were joined together millions of years ago.
         • Large coal deposits that were formed in tropical conditions have been found in North America and parts of Europe. this suggests these regions were once closer to the equator than they are now- they have drifted over time.

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