The table below shows the fossils of organisms found in various layers of an undisturbed rock:

Fossils In Rock Layers

Layer (from top) Fossils in Layer

1 X, W

2 W

3 Z

4 Y, U

Which statement about the organisms whose fossils are found in the rock is correct?

Organism W existed much before Organism Y.

Organism Y existed over the longest period of time.

Organism Y and Organism U were alive over the same time span.

Organism W existed over a shorter period of time than Organism X.

Answer: Organism Y and Organism U were alive over the same time span.

Explanation:I took the test right now

Organism Y and Organism U were alive over the same time span.

Explanation:

According to the Law of Superposition, rock layers and fossils that come with it are older than the layers on top of it. So if you look at your list, rock layer 4 is the oldest layer/fossils and gets younger as it goes up.

The fossils in rock layer 4 are Y and U and this makes them the oldest fossils and you do not see them in any other rock layer, this means that they did not exist anymore when the other layers formed. This rules out statement 1.

U existed along with Y so this rules out statement 2. As for the last statement, look at organism W, it is found in both layer 2 and layer 1. This means that it still existed when layer 1 was forming, so it already existed before organism X appeared.