This process distributes heat and soluble nutrients around the world. As it rises, it cools and becomes less dense than the air around it, spreading out and descending toward the equator again. Atmospheric convection currents are also what keep clouds aloft. Geologists believe the molten rock deep within the earth circulates by convection currents. These constantly circulating cells of hotter and cooler molten rock are thought to help heat the surface. Some geologists believe convection currents within the earth are a contributing cause of volcanoes, earthquakes and continental drift.
Herb Kirchhoff has more than three decades of hands-on experience as an avid garden hobbyist and home handyman. Since retiring from the news business in , Kirchhoff takes care of a acre rural Michigan lakefront property and applies his experience to his vegetable and flower gardens and home repair and renovation projects. The Definition of a Convection Cell. What Causes Convection Currents on the Mantle?
Allow the water to stand about 5 minutes. Fill a small container with very cold water. Add a drop of blue food color. Fill another small container with hot water. Add a drop of red food color. Use a medicine dropper to release a drop of hot, red water at the bottom of one cup. Observe and record the results. Repeat, releasing the water on the surface. Record the results. In the second cup, repeat the process using the cold, blue water. What can you determine about warm water? Cold water? Which is more dense?
In the third cup, simultaneously release hot, red water on the bottom and cold, blue water at the surface. Poke a few small holes in the paper cup. Put the blue ice cubes in the paper cup. Tape the cup to the side of the aquarium.
The hot water moves to the surface, then spreads out and cools. Cooler water sinks to the bottom. Magma is the molten rock below the crust, in the mantle. Tremendous heat and pressure within the earth cause the hot magma to flow in convection currents. Based on evidence that has been found at plate boundaries, make some hypotheses about the movement of those plates.
The earth has changed in many ways since it first formed 4. They have gradually moved over the course of hundreds of millions of years—alternately combining into supercontinents and pulling apart in a process known as continental drift.
The supercontinent of Pangaea formed as the landmasses gradually combined roughly between and mya. It is widely accepted by scientists today. Earthquakes and volcanoes are the short-term results of this tectonic movement. The long-term result of plate tectonics is the movement of entire continents over millions of years Fig. The presence of the same type of fossils on continents that are now widely separated is evidence that continents have moved over geological history. Evaluate and interpret several lines of evidence for continental drift over geological time scales.
The shapes of the continents provide clues about the past movement of the continents. The edges of the continents on the map seem to fit together like a jigsaw puzzle. For example, on the west coast of Africa, there is an indentation into which the bulge along the east coast of South America fits.
The shapes of the continental shelves—the submerged landmass around continents—shows that the fit between continents is even more striking Fig. Some fossils provide evidence that continents were once located nearer to one another than they are today. Fossils of a marine reptile called Mesosaurus Fig. Another example is the fossil plant called Glossopteris, which is found in India, Australia, and Antarctica Fig.
The presence of identical fossils in continents that are now widely separated is one of the main pieces of evidence that led to the initial idea that the continents had moved over geological history. Evidence for continental drift is also found in the types of rocks on continents. There are belts of rock in Africa and South America that match when the ends of the continents are joined.
Mountains of comparable age and structure are found in the northeastern part of North America Appalachian Mountains and across the British Isles into Norway Caledonian Mountains. These landmasses can be reassembled so that the mountains form a continuous chain. Evidence from glacial striations in rocks, the deep grooves in the land left by the movement of glaciers, shows that mya there were large sheets of ice covering parts of South America, Africa, India, and Australia.
These striations indicate that the direction of glacial movement in Africa was toward the Atlantic ocean basin and in South America was from the Atlantic ocean basin. This evidence suggests that South America and Africa were once connected, and that glaciers moved across Africa and South America. There is no glacial evidence for continental movement in North America, because there was no ice covering the continent million years ago.
North America may have been nearer the equator where warm temperatures prevented ice sheet formation. Mid-ocean ridges or spreading centers are fault lines where two tectonic plates are moving away from each other.
Mid-ocean ridges are the largest continuous geological features on Earth. They are tens of thousands of kilometers long, running through and connecting most of the ocean basins. Oceanographic data reveal that seafloor spreading is slowly widening the Atlantic ocean basin, the Red Sea, and the Gulf of California Fig.
The gradual process of seafloor spreading slowly pushes tectonic plates apart while generating new rock from cooled magma. Ocean floor rocks close to a mid-ocean ridge are not only younger than distant rocks, they also display consistent bands of magnetism based on their age Fig.
Geomagnetic reversal allows scientists to study the movement of ocean floors over time. Paleomagnetism is the study of magnetism in ancient rocks. In other words, the particles will point in the direction of the magnetic field present as the rock was cooling.
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