Goal 11 Fossils and the Stories They Tell

Once there were dinosaurs. They roamed the earth for 140 million years 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. Tyrannosaurus rex Introduction

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? Giant ground sloth Have students brainstorm and respond to the question before continuing. Introduction

Fossils form a diary telling the story of the earth’s past. 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. Tyrannosaurus rex skull Introduction

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. Is It a Fossil? Yes or No?

What do you think a fossil is? 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? Have students brainstorm and respond to the question before continuing. When consensus is reached, write that definition on the board. Is It a Fossil? Yes or No?

Fossils are the remains of living things. They can be the remains of plants. Fossil leaf Is It a Fossil? Yes or No?

Or they can be the remains of animals 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 alligator Fossil shell Is It a Fossil? Yes or No?

Do you think this is a fossil? Why or why not? 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? Have students brainstorm and respond to the question before continuing. Is It a Fossil? Yes or No?

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. Is It a Fossil? Yes or No?

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. Ask students how the definition on the board could be modified to reflect this new information. Write a revised definition on the board: Fossils are the remains or evidence of living things. Is It a Fossil? Yes or No?

This picture shows an Egyptian mummy. 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? Have students brainstorm at each STOP sign and respond to the question before continuing. Do you think the mummy is a fossil? Why or why not? Is It a Fossil? Yes or No?

No, an Egyptian mummy is not a fossil. 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. Ask students how the definition on the board could be modified to reflect this new information. (Add that fossils are natural remains.) Write a revised definition on the board: Fossils are the natural remains or evidence of living things. Is It a Fossil? Yes or No?

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

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? Have students brainstorm and respond to the question before continuing.

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

Dendrites can be confusing 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.

This picture shows a kind of mineral crystal called galena 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.

Look at the picture to the left. Is it a fossil, the prehistoric remains or evidence of a living thing? Have students brainstorm and respond to the question before continuing.

While it may look like a human leg, this is a picture of a stone 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.

This picture shows a 40 million year old gnat 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 Ask students if they know what amber is – fossilized tree sap. So this is a fossil in a fossil.

Is It a Fossil? Yes or No? Thumbs up if you think it’s a fossil. Review the final definition of a fossil as written on the board before telling students they will now have an opportunity to use the definition to classify items as fossils or not fossils.   Thumbs down if you think it’s not.

Is It a Fossil? Yes or No? Solicit student opinions, with thumbs up indicating a belief that it’s a fossil and thumbs down indicting a belief that it’s not a fossil. Ask students to state the reasons for their choice. Ant preserved in amber. (It’s a fossil because it’s the remains of a prehistoric animal trapped in amber.) It’s a fossil in a fossil.

Is It a Fossil? Yes or No? 1,600 year old human body preserved in a peat bog. Tell students the high acidity of the peat kept the body from decaying. (Not a fossil because it’s not prehistoric.)

Is It a Fossil? Yes or No? Fossil dinosaur nest. (A fossil because it’s evidence of a prehistoric animal.)

Is It a Fossil? Yes or No? Dendrite mineral deposit. (Not a fossil because it’s not from a living thing.)

Is It a Fossil? Yes or No? Coprolite – fossilized feces. If students are uncertain, tell them what the image shows. (A fossil because it’s evidence of a living thing.)

Is It a Fossil? Yes or No? Fossilized dinosaur skin. If students are uncertain, tell them what the image shows. (A fossil because it’s the remains of a prehistoric animal.) Optional: Ask students to describe what the fossil dinosaur looked like. Compare this with the way in which dinosaurs are depicted in books.

Is It a Fossil? Yes or No? Fossil human footprints; 200,000 years old. (A fossil because it’s evidence of a prehistoric animal.)

Is It a Fossil? Yes or No? Fossil worm burrow). If students are uncertain, tell them what the image shows. (A fossil because it’s evidence of a prehistoric animal.)

Is It a Fossil? Yes or No? Preserved ripple marks from the bottom of an ancient stream. (Not a fossil because it’s not from a living thing.)

Is It a Fossil? Yes or No? Preserved mud cracks. (Not a fossil because it’s not from a living thing.)