Scientists Think That the Life We Have on Earth Today

Multiple Choice

Scientists think that the life we have on Earth today originated some time between 3.5 and 3.8 billion years ago. Yet the solar system and the Earth are known to be at least 4.5 billion years old. Which of the following is one reason life as we know it had to wait until 3.5 to 3.8 billion years ago to get going?

A) supernovae were exploding near the Sun's location every year back then
B) the Sun was so much cooler when the Earth formed, that the Earth's oceans (and even Mars' oceans) were frozen over for billions of years
C) before 3.8 billion years ago, the Earth was experiencing a period of heavy bombardment, when giant chunks of rock and ice left over from planet formation kept hitting our planet and making it uninhabitable
D) experiments like the one done by Miller and Urey show that life on Earth could not form until plants produced a lot of oxygen for our atmosphere
E) the early solar system was filled with dark matter, and life could not form with so much dark matter around