__ 3. Which era of Earth's history could be named the era of mammals? A. Cenozoic era B. Mesozoic era C. Paleozoic era D. Precambrian __ 4. While looking for fossils on an eroded hillside, you discover fossil coral and fish in one layer. In a layer just above, you find the fossil imprint of a fern frond and some fossil moss. Assuming the rock has not been disturbed, which of the following is the most probable conclusion? A. The area had been a sea until recent times. 8. A forest had once grown there but had become submerged by water. C. In ancient times a sea had been replaced by land. D. A saltwater sea had changed to a freshwater lake long ago.

## Step1<br />For question 3, we need to identify the era of Earth's history that is known as the era of mammals. The Cenozoic era is the most recent of the three major subdivisions of the Phanerozoic Eon, spanning from 66 million years ago to the present. It is characterized by the dominance of mammals, hence it is often referred to as the "Age of Mammals".<br /><br />## Step2<br />For question 4, we are given a scenario where fossil coral and fish are found in one layer, and fossil moss and fern fronds are found in a layer just above. This suggests a transition from a marine environment to a terrestrial environment. The presence of coral and fish fossils in the lower layer indicates that the area was once underwater, while the presence of fern fronds and moss fossils in the upper layer suggests that the area was once a forest. Therefore, the most probable conclusion is that the area had once been a sea that was replaced by land.