Answer
a.
Work Step by Step
The big bang theory explains that at one single point in time and space, all matter and energy in the universe appeared all at once, and everything exploded from this single point. This single point from which all matter and energy in the universe was born happened between 13 and 15 billion years ago. The first elements formed were hydrogen and helium. Within our solar system, our sun appeared first, and then an accumulation of rocks and debris that was orbiting the sun became the planets, which includes our earth.
