Big+Idea+3-4+Earth

The earth system changes constantly as air, water, soil, and rock interact, and the earth is a part of a larger sun, earth, moon system.

 * Like all planets and stars, Earth is roughly spherical in shape.
 * Anything on or near the earth is pulled downward by the earth's gravity.
 * Earth rotates on its axis once every 24 hours giving rise to the cycle of night and day and making it seem as if the sun, moon, stars, and planets orbit the earth once each day.
 * Objects in the sky have patterns of movement that can be observed.
 * When liquid water disappears, t turns into a gas (water vapor) in the air. It can reappear as a liquid when cooled or as a solid when cooled further.  Clouds and fog are made up of tiny water droplets or ice crystals.  When such droplets or crystals get large enough, they fall as precipitation.
 * Water from precipitation can seep into the ground, run off, or evaporate. Most of it eventually flows through streams, rivers and lakes and returns to the ocean.
 * Weather variables such as temperature, barometric pressure, wind direction and speed, cloud cover, and precipitation change in predictable patterns.
 * Rock is composed of different combinations of minerals. Smaller rocks come from the breakage or of larger rocks.
 * Soils develop by the breakdown of rocks by weathering and the addition of organic material. Soil also contains many living organisms.
 * Earth processes occur over such long time spans and such large areas that maps and models are used to help understand them.

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