Fossils

Most living things that have ever been on Earth are now extinct. We know about them from fossils. A fossil is the remains of an ancient living thing that has been preserved in the Earth’s crust. Most things that die will not become fossils. It takes a lot of special conditions for them to form.

According to the passage, most things that ever lived are

• fossils.

• extinct.

• animals.

• still alive.

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NGSS.MS-LS4-1

Which of these describes a fossil?

• a desert that used to have a body of water in it

• a species that no longer lives anywhere on Earth

• a scientist who studies the history of life on Earth

• an ancient organism or its trace that has been preserved

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NGSS.MS-LS4-1

NGSS.MS-LS4-2

When people think of fossils they often think of dinosaur bones. But fossils are more than bones, and they don’t all come from dinosaurs or even animals. Plants can fossilize, too. Two main types of fossils are body fossils and trace fossils. Bones, shells, seeds, teeth and leaves are all examples of body fossils. They were actual parts of the plant or animal that died. Nests, footprints, dung and bite marks are all examples of trace fossils. They are things the plant or animal left behind. Trace fossils were not part of the organism’s body. Instead, they are clues that the organism was present.

Which of these is a trace fossil?

• an oyster shell

• an ancient fern leaf

• an ancient bird nest

• a dinosaur’s jaw bone

Which of these is an example of a body fossil?

• woolly mammoth footprints

• a T. Rex bite mark

• a dodo bird nest

• a shark tooth

In order to become a fossil, specific conditions need to be met. An organism needs to die in the right place. It must avoid scavengers and decomposers that would destroy its remains, and it needs to have hard body structures. Soft body structures will decay. Even if a fossil does form, it might not be found. Fossils are sometimes crushed, weathered, eroded and even melted before they are ever discovered.

Based on the passage, which of these best describes fossils?

• rare to find and hard to form

• often formed but never found

• always crushed and often soft

• common to find and easy to form

Tags

NGSS.MS-LS4-1

Which of these is most likely to fossilize?

• a jellyfish’s very soft body

• fruit with a high water content

• a crab claw, which is very hard

• a horse’s mane, which is made of hair

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NGSS.MS-LS4-1

NGSS.MS-LS4-2

An animal with sharp teeth likely ate

• nuts.

• meat.

• grass.

• leaves.

Fossils can tell us a lot, but they can’t tell us everything. Think of everything you know about what a mouse looks like, its diet and behavior. If mice went extinct, what parts would fossilize? Its tail, fur and organs would not. They are too soft to be preserved. Future paleontologists would have to make a guess about what their brain looked like by studying their skulls. Paleontologists wouldn’t know what mice fur looked like, what colors it could be or it it had a pattern. As new fossils are added to the fossil record, we learn more. But Earth’s history still holds many mysteries.

The fossil record can best be described as

• too large.

• unhelpful.

• incomplete.

• not growing.

Tags

NGSS.MS-LS4-1

Animal footprints might give clues about all of these except the animal’s

• diet.

• size.

• weight.

• behavior.