On the geologic time scale are marked by major, striking, and worldwide changes in the type of fossils present. a. eras c. epochs b. periods d. all of the above

Option (A)

Explanation:

Eras are the biggest unit of the geological time scale, which are mainly split into 3 types, namely the Paleozoic, Mesozoic, and Cenozoic.

The Paleozoic era refers to the foremost era of the geological time scale, which ranged from about 540 million years to 250 million years back. During this initial time, there occurred the first index fossils, Trilobites, and ammonoids, which were evolved from the first unicellular organisms that first originated about 3.8 billion years back. It is during that time when the fishes, reptiles and many others first appeared and were abundantly present. The Mesozoic era refers to the age of dinosaurs, which ranged from about 250 million years to 65 million years. After the Cretaceous-tertiary major mass extinction event, the large and complex organism dinosaurs appeared which dominated the earth globally. Lastly is the Cenozoic era, which comprises the recent era which ranges from about 65 million years back to the recent. It is mainly characterized by the occurrence of mammals, horses, elephants, and humans and their evolutionary trend. This is the youngest era.

Thus, the era of the geological time scale is mainly marked by the major, and minor changes that appeared in the fossil assemblages.

Hence, the correct answer is option (A).

on the geologic time scale are marked by major, striking, and worldwide changes in the type of fossils present.
a.
Eras