Big+Idea+5-7+Earth

Solid, liquid, and gaseous earth materials all circulate in large scale systems at a variety of time scales, giving rise to landscapes, the rock cycle, ocean currents, and weather and climate.

 * The earth is mostly rock, with a metallic core, a thin layer of water covering about 3/4 of the surface and surrounded by a thin blanket of air.
 * Everything on or near the earth is pulled toward Earth's center by a gravitational force.
 * Because Earth turns daily on an axis that is tilted relative to the plane of Earth's orbit, sunlight falls more intensely on different parts of the earth during different parts of the year, producing the seasons and seasonal patterns in weather.
 * The moon's revolution around the earth once in about 28 days changes what part of the moon is lighted by the sun and how much of that part we can see from the earth, giving rise to the phases of the moon.
 * The cycling of water in and out of the atmosphere plays an important role in determining climatic patterns.
 * The atmosphere is heated by the sun and by the ground (which is heated by the sun) and oceans, leading the atmosphere to circulate in large scale patterns which help to steer weather systems. Large scale wind patterns also drive surface currents in the oceans.
 * The circulation of the ocean and atmosphere carries heat energy and has a strong influence on climate around the world.
 * Interaction of circulating air masses gives rise to a wide variety of weather phenomena including fronts, mid-latitude cyclones (and anti-cyclones), and severe weather (tropical storms, tornados, severe thunderstorms, etc.).
 * Heat flow from the earth and motion within the earth lead the outer shell of the earth to move around in large rigid pieces (plates) and leads to the creation and destruction of ocean basins, motion of continents relative to one another, earthquakes, volcanic eruptions, and development of mountain belts.
 * Some changes in Earth's surface are abrupt, such as earthquakes, volcanos, meteor impacts, and landslides. Others are gradual, such as the lifting up of mountains or their wearing away by erosion.
 * Sediments consisting of eroded materials (and sometimes the remains of organisms) can be buried by younger layers of sediment and be compressed and cemented together to form solid rock again.
 * Sedimentary rocks buried deeply enough may be reformed by heat and pressure into new rocks, perhaps by melting and then crystallizing or perhaps by recrystallizing while remaining solid. These rocks may be forced up again to the surface by mountain building.  Once exposed again by erosion, the geometry, sequence, and textures of those rocks and rock layers can be used to infer their history.
 * Thousands of layers of sedimentary rock confirm the long history of the changing surface of the earth and the changing life forms whose remains are found in successive layers.
 * Earth materials (rocks and soils) can be classified by their composition and texture and those features can be interpreted to infer the history of the material.
 * Human activities change land cover and land use patterns, add or remove nutrients from ecosystems and modify some of the fundamental cycles of the earth system, including the carbon cycle. These changes can have unexpected and far-reaching effects due to the complex interconnections among earth systems.

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