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By the end of the 2nd grade, students should know that
- Water can be a liquid or a solid and can go back and forth from one form to the other. If water is turned into ice and then the ice is allowed to melt, the amount of water is the same as it was before freezing. 4B/P2
By the end of the 5th grade, students should know that
- When liquid water disappears, it turns into a gas (vapor) in the air and can reappear as a liquid when cooled, or as a solid if cooled below the freezing point of water. Clouds and fog are made of tiny droplets or frozen crystals of water. 4B/E3*
By the end of 8th grade, students should know that
- Eight planets of very different size, composition and surface features move around the sun in nearly circular orbits. Some planets have a variety of moons and even flat rings of rock and ice particles orbiting around them. Some of these planets and moons show evidence of geologic activity. The Earth is orbited by one moon, many artificial satellites and debris. 4A/M3
- Many chunks of rock orbit the sun. Those that meet the Earth glow and disintegrate from friction as they plunge through the atmosphere -- and sometimes impact the ground. Other chunks of rock mixed with ice have long, off-center orbits that carry them close to the sun, where the sun's radiation (of light and particles) boils off frozen materials from their surfaces and pushes it into a long, illuminated tail. 4A/M4*
- The Earth is mostly rock. Three-fourths of the Earth's surface is covered by a relatively thin layer of water (some of it frozen), and the entire planet is surrounded by a relatively thin layer of air. 4B/M2ab*
National Science Education Standards
Earth and Space Science -Content Standard D
PROPERTIES OF OBJECTS AND MATERIALS
Materials can exist in different states -- solid, liquid and gas. Some common materials, such as water, can be changed from one state to another by heating or cooling.
PROPERTIES AND CHANGES OF PROPERTIES IN MATTER
A substance has characteristic properties, such as density, a boiling point and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.
EARTH IN THE SOLAR SYSTEM:
The Earth is the third planet from the sun in a system that includes the Moon, the sun, seven other planets and their moons, and smaller objects, such as asteroids and comets.
STRUCTURE OF THE EARTH SYSTEM
Water, which covers the majority of the Earth's surface, circulates through the crust, oceans and atmosphere in what is known as the "water cycle." Water evaporates from the Earth's surface, rises and cools as it moves to higher elevations, condenses as rain or snow, and falls to the surface where it collects in lakes, oceans, soil, and in rocks underground.
Water is a solvent. As it passes through the water cycle it dissolves minerals and gases and carries them to the oceans.
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