Geologists have divided earth's history into time units, which are largely based on

a. oral histories.
b. fossils.
c. climates.
d. written correspondences.

Geologists have divided Earth's history into time units, which are largely based on fossils.

 

Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past.

 

The correct answer between all the choices given is the second choice or letter B. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.

Geologists use fossils to divide the world's history into eras and periods. Fossils of organisms,  plants and animals are old traces that can be used to determine the era which it belongs. Its age is determined through the conventional method: carbon dating. 

1920 census

the census was scheduled for january the 1st, as the government believed that more farmers would be in their homes by that time instead of april. the census did not ask about unemployment, the number of children, and how long was a couple married were not taken into consideration. individuals were considered as residents of the places they normally slept, not the places were they worked at or visited.

2010 census

the census was scheduled for april 1st, 2010. it was the shortest census in history: it only contained 10 questions related to name, age, gender, ethnicity, relationship, and whether the citizen owned a home or rented one. the government launched a website in order to provide the citizens with information regarding the census. there were also "teach census weeks" in schools nationwide.