fossil

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Fossilsand theStoriesThey Tell

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Table of Contents

Introduction……………………………………………3

Is It a Fossil? Yes or No?…………………………..8

How Do Fossils Form?…………………………….12

What Stories Do Fossils Tell?……………………22

Introduction 3

Tyrannosaurus rex

Once there were dinosaurs. They roamed the earth for 140 million years. But about 60 million years ago, the last of the giant dinosaurs died out long before there were people to see them, tell about them, or draw their pictures.

Introduction 4

Giant ground sloth

Once there were giant ground sloths as big as the elephants that live today. But about 25 thousand years ago, like the dinosaurs, they all died out before any people saw them.

How do we know about animals from long ago that no longer live on earth?

Introduction 5

Tyrannosaurus rex skull

We know about dinosaurs and giant ground sloths because we have found their fossil bones.

Fossils form a diary telling the story of the earth’s past.

But that diary can’t be read by people who don’t know about fossils.

Introduction 6

Giant ground sloth skeleton

This presentation will teach you some of the things you need to know in order to read the fossil diary. You’ll learn just what is and is not a fossil.

You’ll also learn about four ways fossils can be made, and finally, you’ll learn some of the stories fossils tell about what the earth was like long ago.

Introduction 7

After learning these things, you, too, will be able to look at a fossil and read it like a book.

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Is It a Fossil? Yes or No?

Is It a Fossil? Yes or No? 9

Detective’s Guide

After you complete Is It a Fossil? Yes or No?, you will be able to identify an object as a fossil or not a fossil, and give a reason for your choice.


Fossils form a diary telling the story of the earth’s past. But reading and understanding the fossil diary can be tricky because there are many pages missing.

Some were destroyed by changes in the earth. Some have not been found. Still other pages are blank.

These pages were never written on because most living things do not become fossils when they die.


Because the fossil diary of the earth’s past can be so tricky to read, if you want to understand the story it tells, you’ll need to become a fossil detective. Just as police detectives use clues to figure out what happened at the scene of a crime, fossil detectives use fossil clues to help figure out the story of what happened on earth long ago.

These fossil detectives are called paleontologists. Paleontologists are scientists who look for fossils to try and fill in the missing pages of the fossil diary to better understand the earth’s past.

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When conducting an investigation, what’s the first thing a detective needs to do? Find clues. The trick is, what’s really a clue and what isn’t?

When a police detective studies the scene of a crime, there are many things to look at, but only some of them are really clues that will help solve the crime.

The same is true for fossil detectives. When paleontologists look for fossil clues, they have to be able to tell if what they are looking at really is a fossil or not.


To know if something is a fossil or not, you have to know exactly what a fossil is.

What do you think a fossil is?


Fossils are the remains of living things.

They can be the remains of plants.

Fossil leaf


Or they can be the remains of animals. Animal fossils are usually shells or bones. The shells or bones are usually quite heavy, as they have been “turned into stone”. They are also usually a different color from when they were alive.

Fossil shell Fossil alligator


But do fossils have to be the actual remains of a living thing? The picture below shows the footprints of a snipe-like shore bird that lived among the dinosaurs about 100 million years ago. No bones of this bird are known to exist.

Bird footprints

Do you think this is a fossil? Why or why not?


Fossil dinosaur footprint

Yes, the footprints are fossils. Fossils aren’t just the remains of living things. Fossils can be something that a living thing made.


Fossil dinosaur tracks

Footprints are not parts of a living thing. But they were made by living things.

Because they were made by living things, they are evidence that a living thing was there.


So, fossils are more than just the remains of living things. Fossils are the remains or evidence of living things.

Egyptian mummy

This picture shows an Egyptian mummy.

Is the mummy the remains of a living thing?

Do you think the mummy is a fossil? Why or why not?


No, an Egyptian mummy is not a fossil.

Egyptian mummy

How was the mummy formed? Priests took the dead person’s body and cut out the internal organs, dried out the rest of the body with a chemical called natron, rubbed oils on the body and wrapped it in linen.

In other words, the mummy was made by man. That’s why the mummy isn’t a fossil. Fossils have to form naturally, without any help from man.


Hieroglyphic writing

The Egyptian mummy isn’t a fossil for another reason. It’s not old enough.

Fossils are prehistoric. Prehistoric means that it comes from a time before people could record their history. But Egyptians wrote about their lives using hieroglyphics.

Because the mummy comes from a time when people were recording their history, the mummy is not prehistoric, so it isn’t a fossil. People started writing and recording their history about four to five thousand years ago.

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Cave man skull

What about the bones of a cave man? Cave men drew pictures of animals on the walls of their caves.

Would the bones of a cave man be a fossil?

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Cave paintings

Yes, the bones of a cave man would be a fossil. While the pictures cave men made show animals that lived at the time, the pictures don’t record the history of the cave men. Because people started writing their history about four to five thousand years ago, for something to be a fossil it has to be older than that.

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So, as fossil detectives, we now know exactly what kind of clues we’re looking for as we search for missing pages of the fossil diary.

Fossils are the natural remains or evidence of living things from prehistoric times.

Trilobite

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But sometimes it’s hard to tell if something is really the prehistoric remains or evidence of a living thing. Look at the picture. What do you think it shows?

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Dendrite

Later the water dried up, leaving the manganese behind. The pattern looks like a tree or fern, but it’s not.

While it may look like a fossil plant, this is a picture of a type of mineral deposit called a dendrite.

The mineral manganese was dissolved in water. The water seeped into the rock.

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Dendrites can be confusing. The best way to identify a dendrite is by how flat it is. Dendrites are usually as flat as a drawing on a piece of paper.

Fossils are usually not flat. You can see the rounded shape of the plant fossils on the right.

Plant fossil

Another clue is that dendrites follow the cracks in stones, sometimes turning as much as ninety degrees. That’s because they were formed by flowing water which seeps along cracks.

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This picture shows a kind of mineral crystal called galena. Some people are fooled by such crystals and think they are fossils.

But just like the dendrite, mineral crystals aren’t from living things, so they aren’t fossils.

Galena

Mineral crystals have repeating geometric shapes rather than the natural curving shapes of living things.

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Look at the picture to the left.

Is it a fossil, the prehistoric remains or evidence of a living thing?

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While it may look like a human leg, this is a picture of a stone. The stone just happens to be shaped like a human leg.

Because it’s not from a living thing it’s not a fossil.

One way to keep from being fooled by an unusually shaped stone is to remember that animal fossils usually show only the hard parts of a body, like the shell or bones. But in some very rare cases, that’s not always true.

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This picture shows a 40 million year old gnat. The entire body of the gnat has been preserved in a clear stone called amber.

Gnat preserved in amber

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Thumbs up if you think it’s a fossil.

Thumbs down if you think it’s not.

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Practice 1: Is It a Fossil? Yes or No?

Directions:

Look at the picture for each question.

On your paper, circle YES if the picture shows a fossil. Circle NO if the picture does not show a fossil.

On the lines, write the reason for your choice.

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1.

YES NO

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2.

YES NO

____________________________________________________________________________________________________________________________________________________________________________________________________

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3.

YES NO

____________________________________________________________________________________________________________________________________________________________________________________________________

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4.

YES NO

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fossil

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