Evolution in 2 sets of fits and bursts

Life on Earth went from single microscopic cells to blue whales and giant sequoias in 3.5 billion years in two distinct bursts tied to the planet's geological evolution, according to a study published in the Proceedings of the National Academy of Sciences on Monday.

This goes against the common hypothesis that life slowly evolved from a single-celled organism to complex multi-celled organisms.

In analyzing fossil records, the study found that the two size jumps were from bacteria to eukaryotic cells, and from unicellular to multi-cellular organisms. Only bacteria-like fossils were found in the first 1.5 billion years of recorded life on Earth, and they did not grow until more complex organisms developed 2 billion years ago after the appearance of eukaryotic cells.