Question

1. what is one reason mammals didnt exist until 200 million years ago, even though fossil evidence supports that life existed on earth up to 3.8 billion years ago?

• early earths atmosphere contained a toxic mix of gases that couldnt have sustained mammals
• early earths atmosphere was too small to hold the gases that were needed to sustain mammalian life
• early earths atmosphere contains a high concentration of oxygen that would have overwhelmed mammals
• early earths atmosphere was glacial from the formation of earth until the evolution of mammals, so it was too cold to sustain life

Explanation:

Early Earth's atmosphere was primarily made of toxic gases like methane, ammonia, and lacked sufficient oxygen for mammals, which are aerobic organisms. The other options are incorrect: Earth's atmosphere was never "too small" to hold necessary gases; early atmospheres had low, not high, oxygen levels; and Earth was not continuously glacial for the entire period before mammals evolved.

Answer:

A. Early Earth's atmosphere contained a toxic mix of gases that couldn't have sustained mammals