Rocky Patterns of Life

The sediments, ash, and other materials that buried these creatures millions of years ago eventually turn into sedimentary rock. The fossils are found inside the rocks and sometimes in plain sight. Paleontologists conduct much patient and careful chipping away of this rock to find fossils. They create a picture of how these ancient animals and plants lived.

Geologists study the Earth's rocks. By analyzing ancient sedimentary rocks, these scientists tell us when the animals lived and when they died. Fossils and rocks are the true storytellers of Earth's history of life. Together they make up the fossil record.

Sedimentary rocks form in layers. Look at the hills and mountains. Can you see where each layer of sedimentary rock ends

Dinosaurs did not live in the Mesozoic seas, but giant marine reptiles did. These predators ruled the waters. Many had snakelike bodies, grew up to 40 feet in length, and had spiky teeth or protruding fangs.


The term "fossil" was first used in 1546 by a German mineralogist and scholar named Georgius Agricola in his book, De Natura Fossilium ("On the Nature of Fossils"). The word comes from the Latin word fossilis, which translates loosely as "anything dug out of the ground." The book described minerals and gemstones in addition to fossils. Agricola noted how fossils looked like living creatures but never mentioned that the fossils were the remains of actual animals or plants that were once alive. This was a subject of great debate, which was not resolved until the early eighteenth century. Agricola made important contributions to geology, mineralogy, and paleontology.

and the next layer begins? As a helpful hint, the rock layers are often different colors, shades, and textures.

The oldest layers of sedimentary rock lie on the bottom. Layer after layer piles up, one on top of the other. It can take over one million years to form just 3 feet (1 m) of sedimentary rock. Think about how many layers of rock have built up over the past 4.5 billion years!

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