Physical properties include the state of matter. We know these states as solid, liquid, or gas. Properties can also include color and odor. For example, oxygen is a gas. It is a major part of the air we breathe. It is colorless and odorless. Chlorine is also a gas. In contrast to oxygen, chlorine is greenish in color. It has a strong, sharp odor. Have you ever smelled cleaning products used around your home? If so, you have probably smelled chlorine. Another place you might smell chlorine is at a public swimming pool. The chlorine is used to kill bacteria that may grow in the water. Other physical properties include hardness, freezing, and boiling points. Some substances have the ability to dissolve in other substances. Some substances cannot be dissolved. For example, salt easily dissolves in water. Oil does not dissolve in water.
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QUESTION: Why is chlorine used in our everyday lives and how?

Fossils can be used to match up rock layers. As organisms change over time, they look different. Older fossils will look different than younger fossils. Some organisms only survived for a short time before going extinct. Knowing what organisms looked like at certain times also helps date rock layers. Some fossils are better than others for this use. The fossils that are very distinct at certain times of Earths history are called index fossils. Index fossils are commonly used to match rock layers. You can see how this works in Figure 2.30. If two rock layers have the same index fossils, then they're probably about the same age.
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QUESTION: How are index fossils useful?

Shelly wanted a puppy. She asked her mommy and daddy every day for one. She told them that she would help take care of the puppy, if she could have one. Her mommy and daddy talked it over and said that they would get Shelly a new puppy. Her mommy took her to the dog pound so that she could choose one that she wanted. All the puppies at the dog pound need a loving home. Shelly went to every cage and looked each puppy in the eyes and talked to each one. After each one, she told her mommy, "No, this isn't the one for me." Finally, she saw a black and white spotted one that she fell in love with. She screamed, "Mommy, this is the one!" Her mommy asked the worker to take the puppy out so that Shelly could make sure. Shelly and the puppy fell in love with each other right away. Shelly and her mommy took the black and white spotted puppy home with them. Shelly was so excited that she talked all the way home. After thinking hard, Shelly had a name for her new puppy, Spot. Now, Shelly has a new best friend and they play together every day when Shelly gets home from school.
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QUESTION: What did Shelly say she would do with the Puppy if she could have one?

Have you ever looked closely at a globe? That continents look like a giant jig-saw puzzle. North America looks like it could fit next to Europe. The edge of South America matches Africa. Scientists noticed these same features. It caused them to start asking questions. They wanted to know if these continents were was connected? If so, how can something so large move so far? What could possibly have enough force to move such a giant slab of rock? Is there other evidence that can provide clues to the past positions of continents? How can answering these questions help us? A scientist named Alfred Wegener had these same questions. Wegener look at rocks on both sides of the Atlantic Ocean. He noticed they were the same type and age. He thought that the rocks must have formed side by side. He proposed that the rocks then drifted apart. One part went with North America. The other part stayed with Europe.
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QUESTION:
Which scientist noticed that rocks were the same on both sides of the Atlantic Ocean?