Our best evidence to data suggests that the Earth formed 46

Our best evidence to data suggests that the Earth formed 4.6 billion years ago. What life forms existed on Earth during the following periods. (Match the correct answer to each question; you may use each answer more than once.) What happened during the first billion years (4.5-3.6 billion years ago)? What happened during the second billion years (3.6-2.6 billion years ago)? What happened during the third billion years (2.6-1.6 billion years ago)? What happened during the third billion years (2.6-1.6 billion years ago)? What happened during the fourth billion years (1.6-0.6 billion years ago)? What happened during the last 600 million years (0.6 billion years ago to present)? A. no life existed B. unicellular life appeared C. unicellular life forms were the only living things on Earth d. multicellular life appeared. E. dinosaurs dominated the entire period F. mammals dominated the entire period

Solution

What happened during the first billion years? (4.6 -3.6 billion years ago?) A. no life existed.

Reason: Earth was formed over 4.6 billion years ago.Before that there was no life.

What happened during the second billion years? (3.6 -2.6 billion years ago?) C.Unicellular life forms were the only living things on earth.

Reason:Unicellular life appeared first about 3.6 billion years ago.

What happened during the third billion years? (2.6-1.6 billion years ago?) B.unicellular life appeared.

Reason:Unicellualr life appeared on earth during this period.

What happened during the fourth billion years? (1.6 -0.6 billion years ago?) D.multicellular life appeared.

Reason:Multicellular life appeared 1.5 billion years ago.

What happened during the last 600 million years (0.6 billion years ago to pesent?) E and F. Dinosaurs dominated the entire period and mammals dominated the entire period.

Reason: Both dinosaurs and mammals appeared in this period .Dinosaurs appeared first and then mammals appeared before extinction of dinosaurs.