The Earth
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Earthquakes within the Earth’s crust can be sudden and disastrous. Scientists cannot accurately predict when earthquakes will occur. Explain why. To obtain full marks you must support your answer with a description of what causes earthquakes. (4 marks)
plate (boundaries) sudden movement / colliding or normally move a few centimetres per year convection currents / driven by heat from radioactive processes / decay the idea of uncertainty with an explanation eg scientists do not know (with any certainty) • what happens under the crust • where the forces / pressure are building up • we cannot measure the forces • when the forces reach their limit (accept continental drift)
Two hundred years ago, scientists thought that the Earth was about 400 million years old. This estimate came from the idea that the centre of the Earth was still molten. More recently, measurement of radioactivity in rocks has shown that the Earth is much older than 400 million years. Suggest one reason why scientists now know that the Earth is much older than 400 million years. (1 mark)
Radioactivity (keeps the core hot) Accept the Earth is not cooling do not accept fossil / rock evidence
Suggest two pieces of evidence that could be used to show that the continents had once been joined (2 marks)
• the shapes of the two continents fit together (like a jigsaw) • the same type of rocks have been found • the same fossils have been found • rising magma rising through a gap under the Atlantic
About fifty years ago, new evidence convinced scientists that the Earth’s crust is made up of tectonic plates that are moving very slowly. Give two pieces of evidence that have helped to convince these scientists that the tectonic plates are moving. (2 marks)
• earthquakes • volcanoes • idea of distance between America and Europe / Africa is increasing e.g.continental drift • oceanic ridges • formation of (new) mountain ranges • formation of (new) islands • magnetic stripes • tsunamis
Suggest two reasons why the other scientists in 1920 thought that Wegener was wrong. (2 marks)
• continents / plates cannot move (thousands of kilometres) • modern / new animals are different • a land bridge (could explain the matching fossils / rocks) accept the continents / plates are attached to the Earth or continents / plates cannot drift / float ignore .no evidence/no proof
Explain how earthquakes are caused. (3 marks)
Movement of (tectonic) plates any two from: - vibration / (shock)waves (in the earth) - caused by convection currents (in the mantle) - heat / energy released from radioactive processes
In terms of what is happening within the Earth, explain the problems of trying to predict earthquakes. (2 marks)
scientists do not know: • what happens under the crust / mantle / under the surface • where forces / pressures are building up • how to measure these forces / pressures • when these forces / pressures reach their limit
Describe what causes the Earth’s tectonic plates to move. (3 marks)
in the mantle any two from: - convection (currents) / movement - radioactivity / radioactive decay / nuclear reactions - releases heat / thermal energy
Give one reason why Wegener’s idea was not accepted in 1915. (1 mark)
no / insufficient evidence / proof / explanation accept there were other theories such as a land bridge / solid crust
The theory of plate tectonics is used to explain why earthquakes occur. Explain how earthquakes occur. (2 marks)
(continental / tectonic) plates move any one from: • (caused by) convection currents (in the mantle) • (driven by) heat (energy) released by radioactive processes / decay • sudden (movement) / vibrations
Suggest why it is difficult to predict when an earthquake will occur. (1 mark)
• do not know / see / able to detect / measure what is happening below the Earth’s crust • build up of pressure between plates is randomly released
In 1915, Alfred Wegener had an idea that the change shown in the diagram was caused by continental drift. Most scientists could not accept his idea. Suggest why most scientists in 1915 could not accept Wegener’s idea of continental drift. (1 mark)
• Wegener had no evidence / proof • other scientists had different ideas / views • did not respect Wegener as a scientist / geologist accept movement too slow to measure accept continents / plates fixed or land bridge
The Earth has a layered structure and is surrounded by an atmosphere. Use this information and your knowledge and understanding to explain how continents move. (3 marks)
any three from: • plates (move) • heat energy / radioactivity (causes) • convection currents • in mantle
Scientists have suggested that the Earth consists of a core, mantle and crust. A ‘traditional’ theory is that the core is made of iron and nickel. A ‘controversial’ theory is that the core is like a nuclear reactor made of the radioactive elements uranium and plutonium. Why can scientists not prove which theory about the core is correct? (1 mark)
cannot get to / reach / drill to / see the core accept the core is (too) far down (into the Earth) / do not know what happens under the crust / Earth’s surface accept it is (too) hot / radioactive
Suggest two pieces of evidence that may have led Wegener to propose his hypothesis that continents move. (2 marks)
• the continents of South America and Africa would have fitted together like a jigsaw • there are matching / similar rocks / fossils on the continents of South America and Africa
Suggest why, in 1920, other scientists thought that Wegener’s hypothesis was wrong. (2 marks)
other scientists thought that continents are fixed / cannot float or Wegener had no evidence to prove that continents can move a land bridge could explain the matching / similar rocks / fossils on the continents of South America and Africa