Question

When in the history of earth did eukaryotes develop?

Answer 1

The first, simplest life forms were prokaryotes—organisms, like bacteria, that don’t

have a nucleus. Prokaryotes have existed on Earth since at least 3.8 billion years ago.

Eukaryotes are organisms with a nucleus. The oldest evidence of eukaryotes is from

2.7 billion years ago. Scientists believe that a nucleus and other organelles inside a

eukaryotic cell formed when one prokaryotic organism engulfed another, which then

lived inside and contributed to the functioning of its host.

Eukaryotes differ from bacteria and other prokaryotes in many ways. Not only did the cell

finally get a nucleus, but also DNA replaced what was likely RNA as a method of self-replication, bringing with it sexual reproduction.

• Eukaryotes are typically much larger than prokaryotes: > 60 microns compared to < 20.

• Eukaryotes contain DNA in a nucleus.

• Eukaryotes can reproduce sexually. Prokaryotes can reproduce only by cell division and,

lacking sex, are essentially clones, making their early evolution proceed much more

slowly than that of eukaryotes. (Some eukaryotes can clone themselves in addition to

sexually reproducing. They choose their method based on environment indicators.)

• Eukaryotes have specialized organelles bound by double-layer cell membranes and

possessing their own genome. Examples: chloroplasts in photosynthesizers and mitochondria in aerobic respirers.