Index fossils

Some fossils tell the age of the rock they are in. An index fossil comes from a kind of living thing that lived for only a fairly short time in Earth's history but spread widely, was plentiful and is easy to recognise; ammonites, trilobites and some microscopic sea creatures are examples. Any layer that holds it formed while that creature lived, so if its species lived around 120 million years ago, so is the layer, roughly. Finding the same index fossil in layers far apart shows those layers are the same age, which lets geologists match layers across a country or an ocean. Oil and gas companies study the tiny fossils in rock samples from exploratory wells to tell which layer they have reached, since oil and gas lie in particular layers.

Depth 1 · Foundation

You can say what makes a fossil a good index fossil, use one to give the rough age of a layer and to match layers in different places, and say why oil exploration studies tiny fossils.

Depths of understanding

1
Foundation
You can say what makes a fossil a good index fossil, use one to give the rough age of a layer and to match layers in different places, and say why oil exploration studies tiny fossils.
Opens after
Fossils, depth 2An index fossil is a fossil read for the age of its layer.Rock layers, depth 2Index fossils give ages to the layers whose order you can already read.

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What's still between you and Index fossils, depth 1, in the order you can learn it.

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This concept

Index fossilsRocks and Soil

Builds onThis conceptFossilsDepth 2 Rock layersDepth 2 Index fossilsRocks and Soil