The oldest rocks found on Earth are about ____ years old.
a. 14 billion
b. 10.5 billion
c. 7.0 billion
d. 3.9 billion
Question 2
Where did the cosmic microwave background (CMB) come from?
a. Photons emitted from the first stars
b. Photons released from hydrogen in our galaxy
c. Light scattered by dust in our Solar System
d. Photons released when electrons and nuclei combined for the first time.