Saturday Feb. 24,2018

This week  we will study the different kinds of Fossils.

I will upload a video and the lesson from the book to help you understand the lesson.

Lesson 3: What Are Fossils?

Vocabulary

A fossil is a trace or the remains of a living thing that died a long time ago. 

Fossils

Think about the “fossils” you made in the Investigate. Did they look like the shell you used? How were they different from the shell? A fossil is a trace or the remains of a living thing that died a long time ago. There are many different kinds of fossils.

Some fossils, such as bones and teeth, look like the actual parts of animals. Slowly minerals replaced the bones.

Other fossils, such as dinosaur tracks in mud, are only marks left behind. These marks are called imprints. The mud hardened, and in time it changed to rock. Some imprints are of animal parts, such as feathers. Other imprints are of leaves

A mold is the shape of a once-living thing left in sediment when the rock formed. The organism that made the mold dissolved, leaving only a cavity shaped like the organism.

A cast forms when mud or minerals later fill a mold. The cast has the actual shape of the organism itself. You made a model of a fossil mold and a fossil cast in the Investigate.

Plant fossils are not as common as animal fossils. That’s because the soft parts of plants are easily destroyed as rocks form.

MAIN IDEA AND DETAILS What are three kinds of fossils? This fossil shows a trilobite, a kind of animal that died out more than 200 million years ago. This fossil shows a trilobite, a kind of animal that died out more than 200 million years ago.

How Fossils Form

Places that have a lot of sedimentary rocks are better for fossil hunting than other places. Why? It’s because what’s left of a once-living thing is sometimes buried in the particles that form sedimentary rock. Fossils often form in limestone and shale.

Few fossils form in metamorphic and igneous rock. The pressure and temperature that form these rocks often destroy plant and animal parts before they can become fossils.

The Science Up Close shows how a fossil might have begun forming millions of years ago. After dying, the animal was quickly covered by layers of sediment. If the animal had not been covered quickly, another animal might have eaten it. After millions of years, the layers of sediment became sedimentary rock. What was left of the animal is now a fossil.

MAIN IDEA AND DETAILS Why are more fossils found in sedimentary rocks than in other rocks?

This shows what the triceratops fossil below might look like

What can a scientist tell about this fossil?

Learning from Fossils

Scientists today use fossils to learn about animals and plants that no longer exist. For example, scientists learn what kind of foods animals ate by looking at the shapes of fossil teeth. The teeth are compared to those of today’s animals.

Fossils also help scientists tell what a place was like long ago. For example, fossil clams in a place show that a sea once covered the area.

Why do scientists dig up dinosaurs very carefully?