Which of the following events separate geologic time into eras and periods?

the appearance and disappearance of volcanoes
the appearance and disappearance of groups of organisms
the creation of new ocean ridges
the number of earthquakes occurring at that time

Hey! Your answer would be the appearance and disappearance of group of organisms . Hope this helps!

Option (2)

Explanation:

The geological time scale refers to the sequential arrangement of all the major and minor events that have taken place in the past. This scale is divided into some major eons and eras and some subdivisions such as period and age.

The eras and periods are primarily marked by the appearance and disappearance of a group of organisms that allowed the geological time to be separated. There are three main eras namely the Paleozoic, the Mesozoic, and the Cenozoic.

The Paleozoic era was marked by the presence of simple organisms and index fossils both in the terrestrial as well as in the marine ecosystem, such as trilobites, fishes, reptiles, brachiopods, bivalves, and gastropods.

The Mesozoic era was marked by the presence of dinosaurs that ruled the earth's surface some 150 million years back. They were dominantly present and scattered in almost all parts of the land.

The Cenozoic era is the third one that is marked by the appearance, evolution, and presence of various groups of organisms such as horses, mammals, and humans.

Thus, the correct answer is option (2).

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.

the dissolution of polymer can be thermodynamically described in 2 steps.