Lesson #14 of 18 in the Brain Makeover collaboration with Professor James Trefil/George Mason University, the 76ers Cheerleaders and the Science Cheerleader. See Brain Makeover Series.
#14: The Earth operates in many cycles.
You can think of the Earth as a giant machine with many gears, but with all of the gears meshing together to make a coherent whole. The planets’ “gears” include three important cycles:
Rock cycle – Rocks first formed from molten material on the early Earth (such rocks are called “igneous“). Material weathered from the rocks was carried down to river deltas and beaches where, over time, it built up to form a different kind of rock, called sedimentary. If tectonic activity lifts a sedimentary rock up, it will weather and contribute to new cycles of rock. Occasionally, sedimentary rocks are buried and, under the influence of heat and pressure, change into a new type of rock (termed “metamorphic“).
Water cycle—Water evaporates from the oceans and falls as rain on land. It eventually flows back into the ocean, either as a surface river or as an underground aquifer. Over long periods of time, the Earth’s water can be taken up in ice caps and glaciers (ice ages) or put back into the oceans.
Atmospheric cycle—The uneven heating of the Earth’s surface and the planets’ rotation cause the atmosphere to move and create our weather. Near the tropics, winds blow from the east (“trade winds“) while farther north they blow from the west (“prevailing westerlies“), then blow from the east again near the poles.