What do fossils tell us about the past? Which of the following occurred as ancient climate changed?
a. During very warm periods, sea levels are very high.
b. During very cold periods, sea levels were very high.
c. Since the Eocene, there has been a general cooling of Earth’s surface temperature.
d. One of the most profound temperature changes, and thus dramatic alterations of climate and habitat, began at the end of the Miocene, around 6 mya.

Fossils can give some information about the species that were living in a certain period of time, also can give some DNA of plants or animals that the were living at that period of time.

Explanation:

during our Earth ages, the climate has been changed several times, in some occasion to give a colder climate, in others, to give a hotter climate. In the Eocene (among 7 - 23 mya), at the beginning the climate was very hot but by passing the time, some parts of the planet like the antarctic, was formed. Also, due to the movement of the tectonic plates, the formation of some mountains like the Alps.

Also, a fossil can give some information of the period that was formed, and also can be useful to observe the species that it belong.

Hope this info is useful.