Why is it that scientists know less about the first four-fifths ...

[ap345]

Why is it that scientists know less about the first four-fifths of Earth's history than about the last, most recent one-fifth?
 
  What will be an ideal response?

Question 2

Assuming that humans went extinct today, do you think that they would be good index fossils? Why or why not?
 
  What will be an ideal response?

[dyrone]

Answer to Question 1

Answer: The short answer is that the farther back in time, the fewer the clues that remain because of two major factors: 1) Precambrian rocks (which make up 88 percent of Earth's history) have been intensely deformed, so evidence was destroyed, and 2) the first abundant fossil evidence does not appear until the beginning of the Cambrian period.

Answer to Question 2

Answer: Yes. Modern humans have only existed for 100,000 years and are geographically widespread.