Regarding the history of the universe, which of the following is true? Regarding the history of the universe, which of the following is true? Key elements of which Earth and life are made, including carbon, oxygen, and iron, did not exist when the universe was born and were created later in stars. All the chemical elements were created during the Big Bang, but some have been modified since that time as a result of radioactive decay. The Earth formed quickly after the Big Bang. All the current stars in our galaxy formed about the same time billions of years ago.

1. The universe consisted of hydrogen and helium initially. This statement is true.

2. It is important to understand radioactive decay in order to understand this question, here's a good analogy:

A snake will shed it's skin, just as an atom will shoot off different parts of itself. It would be very difficult to force that snake to reenter it's skin once it sheds, just as it takes a lot of energy to force fusion of atoms and the parts mentioned. In normal circumstances, nuclear decay is one-way.

3. The earth is a giant floating rock in space. It took many many years to gather a bunch of asteroids and dust to make this planet.

4. I shouldn't have to explain this one, it doesn't make much sense.