Fossils are the preserved remains, or traces of animals, plants, and other organisms from the remote past. We can learn a lot about the historical Earth from these remnants.

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What is a Fossil?

Fossils can be the actual remains of an animal turned into rock or can simply be impressions left behind, like stamps. Fossils usually occur in sedimentary rock. This type of rock is formed when sand or mud settles at the bottom of seas, rivers, lakes, or marshes.

Sediment or layers of dirt build upon each other, putting pressure on the lower layers until after thousands of years, rock is formed.


Tyrannosaurus Rex fossil on display. Completely preserved skeletal fossils like this one are rare.

TrilobiteSmithsonian National Museum of Natural History


Trilobites are animals that played an important role in our planet’s history. We discovered them when we found their fossils.

Fossilized dinosaur eggs by Photo: AMNHAmerican Museum of Natural History


Similar to teeth, animal eggs can be fossilized too.

How are Fossils Formed?

Fossils form when animals die in specific conditions that allow their remains to be fossilized before they decompose or are eaten. For example, a dinosaur could have died on the shore of a lake. 

Over time, it could have rotted and its bones washed into the lake, where they were covered with sand, and layer upon layer of sediment covered that sand. Time passed until the sand and sediment turned into sedimentary rock.

Eventually, the bones also turned to rock as the organic material was replaced by minerals.


The dinosaur roams the land.

Lakeshore Death

The dinosaur dies near a lake.

Cover Up

Mud and sediment build up, covering the dinosaur. The lake dries up and the dinosaur remains buried.


As the earth shifts, the dinosaur bones could be shifted, exposed to the weather, or kept underground until they  are discovered millions of years later!

Types of Fossils

There are two main types of fossils: fossilized body parts and fossilized traces. Fossilized body parts are preserved remains of animals such as bones, teeth, shells, or even eggs. Although sometimes softer parts of the bodies are fossilized, this is rare.

Usually, softer parts decompose or rot more easily, meaning they aren’t preserved. Sometimes, minerals replace the actual body parts. Fossilized traces refer to signs of presence left by animals such as footprints, skin prints, nests, tooth marks, or even feces. 

Body Fossils

Fossilized shells are an example of body fossils. Other types of body fossils are bones and teeth.


Dinosaur eggs are another example of body fossils. Shells are made up of mostly calcium carbonate.


Skin impressions are examples of fossilized traces. Due to the composition of the soft tissue, skin itself cannot be fossilized.

Fossilized Feces

Coprolite or fossilized dinosaur feces also fall into the fossilized traces category. They are considered trace fossils because they allow us to understand the animals’ behavior (what they eat, etc), rather than the animals’ physiology.

What is a Paleontologist?

Paleontologists are scientists who look for and study fossils. The name comes from the Greek words “paleo,” which means old or ancient; “ontos,” which means being or creature; and “logos” which means study or thought.

These scientists must study a combination of biology and geology, although there are many different specializations within paleontology.


Paleontologists use many tools to clean and examine the fossils. Here, a brush is being used to clean dirt off a bone segment.

Cuvier Georges (1762-1832)LIFE Photo Collection


Georges Cuvier, the father of paleontology. He has done extensive work on the classification of animals as well as the studying of fossils.

Animal Chart

This is a chart of animals and the time periods in which they lived. It also shows us layers of the Earth where these organisms have been buried as fossils.

Out in the Field

Sometimes, fossils are discovered accidentally by regular people who just happen to stumble across them. Other times, paleontologists identify places they’ve studied and identified as potentially fossil-rich areas.

Upon discovering a fossil, paleontologists must use care and special tools to extract it. 


Barriers are normally placed around a big fossil find to protect the area. Paleontologists may camp out at the excavation site, called a dig, for a long time while they uncover fossils.


Sedimentary rock is analyzed to show age and get samples. Generally, older layers are lower and younger layers are higher.

The Fossil

Paleontologists must work at uncovering a fossil very carefully because of how fragile some of the pieces are.

Special Tools

Paleontologists need special tools such as picks, hammers, chisels, and brushes.

Retaining Wall

Sometimes, retaining walls must be built to make sure the dig area is safe and that the excavated area doesn’t collapse.

What We Can Learn From Fossils

Paleontologists can learn a lot from fossils. They can try to get an idea of what life was like millions of years ago. Through the study of ancient creatures, scientists can learn about past climate changes to predict similar events in the future.


The ancestor to horses, they lived approximately 50 million years ago and are very small compared to a modern-day horse.


Merychippus lived approximately 20 million years ago.

Paleontologists also discover and help preserve biological history, which gives us more of an understanding of our world. The details of how evolution occurred and the clues to the origins of life itself on our planet are found in fossils.


The modern-day horse, or Equus, appeared in the past 1.8 million years.

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