What are Fossils?

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Ancient organisms like plants and animals have left behind incredible clues about their existence. These clues are called fossils.

Fossils can take many forms, including entire organisms, parts like bones or shells, or even traces of activity such as footprints or leaf impressions.

These remains are considered fossils if they are at least 10,000 years old. The oldest fossils, nearly 4 billion years old, are traces of ancient ocean-dwelling bacteria.

In comparison, younger fossils, like woolly mammoth teeth, date back about 10,000 years.

Fossils are grouped into two main types : body fossils and trace fossils. Body fossils are the physical remains of an organism, such as bones, teeth, or shells. For example, a dinosaur skeleton is a body fossil.

Trace fossils, on the other hand, are evidence of organism behavior, like footprints, burrows, or leaf impressions on stone.

Fossils come in all sizes. The smallest are called microfossils, which are only visible under a microscope.

Larger fossils are called macrofossils and can be massive, like dinosaur bones.

Overview

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What are Fossils?

Fossils are like nature’s time capsules. They are the remains or traces of plants and animals that lived long ago, sometimes millions of years ago. These can be bones, shells, footprints, or even leaf imprints. Fossils help piece together what life was like back then. Most of them are found in sedimentary rock, which forms in layers over time. The deeper a fossil is buried, the older it is. Fossils provide clues about how living things and environments have changed over time.

Science and Engineering Practices (SEP): Constructing Explanations and Designing Solutions

To understand the past, scientists gather and study evidence from different sources. Fossils are one of the most important pieces of evidence. By looking at fossils, it is possible to explain how species have changed and how the environment has shifted over time.

Activity Ideas:

Create a Geological Timeline with Fossils – Use a long paper strip to show Earth’s history. Place images of fossils along the strip by age—older on one end, newer on the other. Add labels with periods. This model of the fossil record and geological time scale helps to learn about the history of life on Earth.
Make a trace fossil – Press a shell, leaf, or toy animal foot into clay to leave an imprint. Let it dry. This models how footprints and other traces become fossils and how they tell us about ancient life.

Crosscutting Concept (CCC): Scale, Proportion, and Quantity

Fossils help explain how Earth has changed over time. To understand their impact, it is important to study patterns in scale, proportion, and quantity. These ideas show how small clues from the past reveal big changes across millions of years.

Scale: Geological time scales over which fossils form are vast, spanning millions of years. It's hard to imagine these long timescales, so scientists use models and timelines to help visualize Earth's history.
Proportion: The proportion of certain radioactive elements in surrounding rocks is used to estimate the age of a fossil. The type of rock and the species present can also influence these measurements.
Quantity: Scientists need large quantities of fossils. The amount of time to understand the life of the species helps in understanding the fossils. Fossils can be as tiny as a grain of pollen or as huge as a dinosaur skeleton. No matter their size, they help reveal Earth’s history on a scale too big
to observe directly.

Procedure

Transcript

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