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6.Fossils 2

3 Fossils are usually found in sedimentary rock Vocabulary fossils The remains or the imprint of a plant or animal that died long ago

4 When a dead animal or plant gets covered by sediment, a mold, or cast of the fossil may form

5 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

6 Vocabulary casts A type of fossil that is formed when a mold is filled with minerals that harden into rock

7 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

8 A cast has the same shape as the plant or animal

9 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

10 Traces of animals, such as footprints, may also become fossils Footprints are often found in mud that later hardened into rock

11 Whole plants or animals are the rarest kind of fossil But entire giant wooly mammoths have been found frozen in ice

12 Fossils are an important source of information about the past

13 For example, if scientists find fossils of shells on dry land, they know that part of Earth was once covered with water

14 Remember: Living organisms are made of carbon Carbon-14 is useful in dating fossils, bones and wood up to 50,000 years old

15 Organisms take carbon out of the environment to build tissues in their bodies When the organism dies, the carbon-14 turns into nitrogen-14

16 The amount of carbon-14 can be measured to determine the age of fossils Or when humans first used a fire site!

17 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

18 Vocabulary Carbon dating A method of counting carbon-14 atoms to determine the age of a fossil, bones, or wood