All species on Earth today are descended from a cell that lived as early as ____ years ago.
A)570 million
B)1.4 billion
C)4 billion
D)more than 5 billion
E)more than 10 billion

Question

Quizplus · Accepted Answer

The most recent common ancestor (MRCA) of all living things is estimated to have lived around 3.5-3.8 billion years ago, so all species on Earth today are descended from a cell that lived around that time. Choice A, 570 million years ago, is too recent and refers to the beginning of the Cambrian period when there was a rapid diversification of animal species. Choice B, 1.4 billion years ago, while still quite early in Earth's history, is closer to the time of the first eukaryotic cells. Choices D and E are also too recent and would not account for the diversity and complexity of life on Earth.

All Species on Earth Today Are Descended from a Cell