Author Question: During the Precambrian, the development of the ozone layer helped A) primitive organisms on ... (Read 57 times)

stephzh · **on:** Jul 29, 2018

During the Precambrian, the development of the ozone layer helped

A) primitive organisms on Earth's surface to nucleate.
B) shield Earth's surface from harmful ultraviolet radiation.
C) promote the emergence of stromatolites.
D) promote the development of anaerobic organisms.

Question 2

The oldest known fossils of single-celled organisms are

A) 4.6 billion years old.
B) 3.9 billion years old.
C) 3.3-3.5 billion years old.
D) 1.3-1.5 billion years old.