Evidence from paleontology indicates that the first eukaryotic cells appeared on the earth approximately
2 billion years ago. Some fossilized cells that look remarkably like modern-day algae or protozoa appear in shale sediments from China, Russia, and Australia that date from 850 million to 950 million years ago. While it used to be thought that eukaryotic cells evolved directly from prokaryotic cells, we now believe that both prokaryotes and eukaryotes evolved from a different kind of cell, a precursor to both prokaryotes and eukaryotes that biologists call the Last Common Ancestor. This ancestor was neither prokaryotic nor eukaryotic, but gave rise to both in different ways.