Current scientific estimates indicate that Earth is approximately 4.5-4.6 ________ years old and that life began on Earth approximately 3.2-3.5 ________ years ago.
A) billion; million
B) million; million
C) billion; billion
D) million; billion

Question

Current scientific estimates indicate that Earth is approximately 4.5-4.6 ________ years old and that life began on Earth approximately 3.2-3.5 ________ years ago. 
A) billion; million 
B) million; million 
C) billion; billion 
D) million; billion

Quizplus · Accepted Answer

The estimates for the age of Earth and the onset of life on Earth are given in billions of years, so only options A and C are possible. However, since the estimates for both are in the billions, only option C is correct.

Current Scientific Estimates Indicate That Earth Is Approximately 4