Answer:
Earth formed around 4.54 billion years ago, approximately one-third the age of the universe, by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere and then the ocean, but the early atmosphere contained almost no oxygen.
Explanation:
It would be 100 times greater if you are going from a pH of 5 to 7
the answer is 21<span>% oxygen, </span>
<span>
So that you wont will not crack your head or damage your brain. </span>