Answer to Question 1
C
Answer to Question 2
Life has existed on Earth for at least 3.4 billion years, but there is no evidence of anything more than simple organisms until about 540 million years ago, when life suddenly branched into a wide variety of complex forms. This sudden increase in complexity is known as the Cambrian explosion, and it marks the beginning of the Cambrian period.If you represented the entire history of Earth on a scale diagram, the Cambrian explosion would be near the top of the column. The emergence of most animals familiar to you today, including fishes, amphibians, reptiles, birds, and mammals, would be crammed into the topmost part of the chart, above the Cambrian explosion.