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| Frage | Antworten |
| Who proposed continental drift? | Alfred Wegener |
| Who proposed seafloor spreading? | Harry Hess |
| How was seafloor spreading discovered? | Scientists discovered seafloor spreading because they were dropping very long cables because they had discovered a large mountain range in the middle of the Atlantic Ocean. After WWI, studies showed that the underwater ridge continued into other oceans right around the Earth. In the middle of these ridges were found to have great cracks in the middle. Harry Hess proposed that a new rocky crust was forming at the ridges and spreading outwards. |
| What is the asthenosphere? | The upper mantle layer. |
| What are the characteristics of the asthenosphere? | Very thick, slow moving, liquid, allows tectonic plates to move on it. |
| What is subduction? | An oceanic crust collides with a continental crust then the denser oceanic plate sinks under the continental plate. The continental plate becomes distorted and fold mountains and volcanoes form as well as a deep ocean trench. |
| Why does the more dense oceanic plate sink under the continental plate? | Because the oceanic plate is more dense than the continental. |
| What were the two main observations that led Alfred Wegener to his theory of continental drift? | He noted that the continents appeared as if they all once fitted together and that fossils of the same species were found miles apart and there was no other logical explanation apart from continental drift. |
| What was the name Wegener gave to the big land mass he fitted together? | Pangaea |
| How did Wegener deduce what Pangaea looked like? | By fitting all the continents together. He then said that somehow the continents must have separated and drifted apart. |
| What is seafloor spreading? | It occurs when two plates are moving apart from each other, forming cracks in the surface. Magma comes up between these cracks, cools and forms new rock. This then spreads outwards. |
| What is the evidence to support the theory of seafloor spreading? #1 | The way the mountain ridges extend all the way around the Earth, and are not just in the Atlantic. There are lots of underwater mountain ranges. |
| #2 theory of seafloor spreading | The age of the sea floor varies depending where you look. |
| #3 theory of seafloor spreading | There is magnetic striping in the rock in some areas. |
| Why does magnetic striping exist? | Because when some of the rock was formed the north pole was facing north and when other rock was formed at different times the pole direction had changed direction. |
| Magnetic striping 2 | The rock is then pushed outwards creating a symmetrical pattern of magnetism on either side of the crack in the ridge, because the rock at equal distance from the crack was formed at the same time. |
| Define continental drift | The theory or idea that the continents are moving. |
| Define plate tectonics | The theory or idea of having actual plates that move. |
| Magnetic field reversal is... | the change of direction of the Earth’s magnetic field. |
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