Ursarctian

The Ursarctian Period is the age lasting from 2400 to 1700 million years ago. It is the second period of the Plutolithic Era, bounded by the older Dorasterrolithic below and the younger Argentiferous above. Its name is derived from the scientific name of the Grizzly Bear, Ursus arctos, as the first rocks described from this period were found in the Grizzlybear Territory near what is now Market55.

The only life worldwide at the time was microscopic and single-celled, though colonial bacteria did exist, forming layered mud structures called stromatolites. Though life preceded the Ursarctian by well over a billion years, it was prokaryotic, with simple cells.

The first eukaryotes evolved some time during this period, likely by engulfing smaller bacteria and forming an endosymbiotic relationship with them. Mitochondria, and not long after (geologically speaking) chloroplasts in green algae and plants are simply highly specialized bacteria inside eukaryotic cells. With this breakthrough, eukaryotic microbes began to diversify further as the Plutolithic Era continued- however, multicellular animal life was roughly 700 million years away.