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Continental Drift 2. Schedule. How do the continents move?. 1950s - Scientists begin mapping the sea floor. How would you think the sea floor would look? They thought it would look smooth. Scientists found mid-ocean ridges, or underwater mountains. Mid-Ocean Ridges.
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How do the continents move? • 1950s - Scientists begin mapping the sea floor. • How would you think the sea floor would look? • They thought it would look smooth. • Scientists found mid-ocean ridges, or underwater mountains.
Mid-Ocean Ridges • Form along cracks in the crust • Molten rocks rise though the cracks, cool, and the mountains are formed. • Newer rock comes out, and pushes the older rock away. • Scientists tested rocks and found that the youngest rocks were by cracks in Earth. • The oldest ocean rock is only 160-180 millionyears old. • The continents that we live on is about 4 billion years old.
If we keep getting new rock, why is Earth the same size? • Deep sea trenches • The older crust comes to a trench, and it sinks into the trench. • Old crust is destroyed at the same rate new crust is being formed; this is why we are not getting any bigger. • This proves that Earth is moving!
Why do plates move? • Tectonic plates rest on the asthenosphere. • Rocks move by convection. • Convection - energy transfer by the movement of material • Hot softer rock rises, cools, and sinks, process starts again and again • This is called a convection current. • These convection currents are present in the asthenosphere and mantle.
Plate Tectonic Theory • Theory of plate tectonics - The lithosphere is made up of huge plates that move over the surface of the earth • Plates move over a long period of time in three main ways • Past each other • Move apart • Push together • Earthquakes, volcanoes, and mountain ranges occur when the plates run into each other.
