Good question. Scientists are always trying to answer questions. Some questions might be:

• What animals used to live here?
• How have animals changed over time?
• Are the species we have here now been here for a long time?
• How did this fossil get here?
• How do fossils form or get destroyed?
• How many things died that didn’t fossilize?

Some questions are about patterns in space, time, or something else. Some questions are about processes (how things happen).

Our EXPLANATIONS for patterns like finding clam shell fossils on the top of a mountain are called HYPOTHESES. How would you explain finding clam shell fossils embedded in rock layers on the top of a mountain? Here are a few hypotheses I came up with:

• These are not really clam fossils, they are rocks that just look like clam shells.
• These are weird land clams.
• This mountaintop was once covered with water.
• This mountaintop was once a giant meteor that came from space that got its fossils from another planet.

As you read my list, some of these hypotheses may have seemed more likely than others. Sometimes weird hypotheses are correct. Often they aren’t.

Notice that none of the hypotheses involved supernatural causes like actions by God/gods/spirits or magic. Science cannot say that these things don’t exist, but supernatural explanations cannot be evaluated by science because they do not follow natural laws. They may be valid hypotheses in some belief systems, but they are not valid scientific hypotheses.

Back to your original question, let’s say I find a fossilized bone (I wish!). I can tell it’s made of minerals like silicon dioxide instead of calcium and proteins like a bone would be by doing chemical tests. How do I know it’s not just rock? I can look at its shape on a big scale or a small one. Even on a microscopic level, it will still have patterns like bone. How can I tell what animal it came from? I can compare it to bones of living animals or other fossils. This doesn’t prove that it came from an animal that once existed, but that would be the best explanation I can think of. What would be your explanation?

Thank you for the excellent question. Scientists called paleontologists use fossils to study organisms that lived in the ancient past. These scientists are interested in discovering how long ago different animals lived, how they survived in their environment, and their evolutionary history.

There are two types of fossils, body fossils which are the preserved remains of an organism’s body, and trace fossils, which are things like the footprints of ancient animals. Both types of fossils provide evidence about the nature of ancient types of life billions of years before modern humans existed.

To understand how paleontologists use fossils to make discoveries, first we need to learn about how fossils are made. Sometimes animals get buried under ground, for instance after a flood or volcanic eruption. Over thousands of years the minerals in the ground begin to replace different parts of the animal’s body, in a process called permineralization. Eventually, a rock is formed in place of where the animal used to be. This special rock, or fossil, then provides lots of information about what that animal was like.

With some knowledge about where to look and often a bit of luck, paleontologists carefully dig up fossils and often conduct experiments on them. Studying fossils gives us direct evidence about the size and shape, the anatomy, of an ancient animal. Also, using radiometric dating techniques, scientists can determine how old a fossil is, which lets us know what types of animals were alive during a certain time in the past.

All the known fossils make up the fossil record, which is a history of the all the different things to have ever lived on Earth. Patterns in the fossil record provide evidence about the evolution of life on Earth.

Thanks again for the fascinating question,

Great question. Most forms of life are preserved as fossils, not just animals. Suppose we find a fossil tooth in a sedimentary rock, and suppose further that we can identify that tooth (elephant, let's say), and we know how old that rock layer is (30 million years, let's say), then we can be pretty certain that that particular kind elephant existed at that point in the past. There's really no better way to account for why we find the remains of ancient organisms in ancient rocks other than to say those organisms existed in the past. Some of those organisms might be pretty similar to those still living (elephants, for example), while others might be very different (Triceratops, let's say).

When an animal dies, a fossil of the animal’s bones may form if the conditions are right. Paleontologists (scientists who study fossils) are always discovering fossils that have never been found before, providing support for a new animal discovery! Paleontologists will use the bone structure of fossils and compare them to previous findings to figure out if a new animal has been discovered.

Here is a cool article about a recent dinosaur discovery:
article on fossils

This website talks about how most fossils are formed:
formation of fossils

This is a great video that explains fossils:
video

If the fossil exists, then something had to make that fossil, which means that at one time the animal or plant that made it must have existed. Thus by finding a fossil you are finding evidence of something that once was.