Fossils; The surface

Fossils provide scientists with many clues about Earth's history, offering evidence of dinosaurs and strange plants that existed in the past. This lesson will define a fossil, look at different types and characteristics of fossils, and then describe how fossils are formed.

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Definition of Fossils

Have you ever wondered how scientists know so much about the earth's past? For example, how they know Hadrosaurs, a group of duck-billed dinosaurs, lived in Alaska 90 million years ago? Or how they know a relative of today's horsetail plant lived 150 million years ago?

Paleontologists, or scientists who study fossils, help paint a picture of what life used to look like on earth millions of years ago. Fossils are remains or traces of past organisms that have been preserved by nature. And here's a fun fact: the word 'fossil' is Latin and actually means 'obtained by digging,' which makes sense because they are often buried.

Types of Fossils

There are many ways fossils can form, and we'll get to all that in a minute. First, let's discuss the two main ways that fossils can be classified:

Body fossils and trace fossils

The remains of a Hadrosaur are an example of a body fossil, or fossils of the actual organism. Typically, hard structures like bones, shells, and teeth fossilize more often than soft-bodied structures like tissues or plant leaves, but as is seen with the horsetail relative, plants can become fossils.

The other type of fossil is called a trace fossil, where evidence of the organism but not the actual organism is preserved, such as a track, a burrow, a nest, or even feces.

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Characteristics and Examples of Fossil Formation

The many different ways organisms are preserved gives fossils different characteristics. Let's explore a few ways fossils can form.

Permineralization is when an organism dies and sediment enters the body, filling in the pores of a leaf, or a bone or a shell. Oftentimes, minerals from the sediment will eventually replace the organism's tissues, leaving a replica of the original organism.

Mold fossils and cast fossils occur when an organism leaves an imprint that is fossilized. Mold fossils are when an imprint is made and that imprint is fossilized, whereas cast fossils are imprints that are filled in and then fossilized.

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For paleontologists, finding an organism that is preserved without any changes to its composition is a huge find. For example, when an organism falls in tree amber and then fossilized, the organism is preserved. Thus is called whole body preservation .