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6. Fossils

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Fossils are usually found in sedimentary rock

Vocabulary

fossils

The remains or the imprint of a plant or animal that died long

ago

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When a dead animal or plant gets covered by sediment,

a mold, or cast of the fossil may form

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Vocabulary

mold

A type of fossil that is an empty space formed when the soft parts of dead matter

decay and the sediments around the dead matter harden

into rocks

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Vocabulary

casts

A type of fossil that is formed when a mold is filled with

minerals that harden into rock

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As the sediments harden into rock, the soft parts of the dead

matter will decay

The empty space left in the rock is called a mold

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A cast has the same shape as the plant or animal

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If the mold fills with minerals from water, the minerals may

harden to form a cast.

The cast also has the same shape as the living thing that

died

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Traces of animals, such as footprints, may also become

fossils

Footprints are often found in mud that later hardened into

rock

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Whole plants or animals are the rarest kind of fossil

But entire giant wooly mammoths have been found

frozen in ice

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Fossils are an important source of information about the past

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For example, if scientists find fossils of shells on dry land,

they know that part of Earth was once covered with water

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Remember: Living organisms are made of carbon

Carbon-14 is useful in dating fossils, bones and wood up to

50,000 years old

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Organisms take carbon out of the environment to build

tissues in their bodies

When the organism dies, the carbon-14 turns into nitrogen-14

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The amount of carbon-14 can be measured to determine the

age of fossils

Or when humans first used a fire site!

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Carbon dating can be done on fossils, bones or wood that existed before the 1950’s

Because that is when humans began working with nuclear

materials

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Vocabulary

Carbon dating

A method of counting carbon-14 atoms to determine the age

of a fossil, bones, or wood