How fossils form

Question 1

A geologist studies a canyon and finds three horizontal rock layers. The lowest layer is sandstone that contains many fossilized shells of sea creatures. The middle layer is shale that contains fossilized fern leaves. The top layer is limestone that contains fossilized coral. Which explanation best uses this evidence to describe how the landscape changed over time?

Accepted Answer

The area was first a shallow sea (shells), then a swampy land with ferns, and later a shallow sea again where coral lived.

Answer

A single massive flood deposited all three layers at once, and the fossils were carried from far away.

Answer

The three layers came from three different continents that later collided, so the fossils reflect different continents, not local change.

Answer

The layers are volcanic ash, and the fossils grew on the rocks after they cooled.

Question 2

A geologist looks at a cross‑section of a hill that shows three visible rock layers. The lowest layer contains fossilized trilobites, the middle layer contains fossilized fern leaves, and the top layer has no fossils. Which observation provides the strongest evidence that the landscape has changed over a long period of time?

Accepted Answer

The lowest rock layer contains fossilized trilobites, while the middle layer contains fossilized fern leaves.

Answer

All three rock layers are composed of the same type of sandstone.

Answer

The rock layers all have the same color and texture.

Answer

The top rock layer is the thickest of the three layers.

Question 3

A geologist studies a canyon and observes three distinct rock layers. The bottom layer contains fossilized trilobites, the middle layer contains fossilized fern leaves, and the top layer contains fossilized dinosaur bones. Which piece of evidence most strongly supports the idea that the landscape has changed over a long period of time?

Accepted Answer

The different types of fossils found in each layer.

Answer

The presence of large rocks in the middle layer.

Answer

The varying colors of the rock layers.

Answer

The depth of the canyon.

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