On Old Earth, the first epoch of the Quaternary Period, corresponding to the most recent Ice Age; 2.6 million years ago to 12,000 BT (10,000 b.c.e.) Life forms included the first anatomically modern humans, megafauna such as mammoths, mastodons, sabre toothed cats, giant ground sloths, woolly rhinos, diprotodonts, and other forms, as well as smaller animals. Invertebrates were basically the same as modern forms. A mass extinction of large mammals and many birds occurred at the end of the epoch, caused by a combination of climate change and human impact.
"Back to the Pleistocene" became a popular slogan among many eco-activist extremist groups of the Information Age and Interplanetary Age, who wished to reconstruct or return Earth to its pristine condition. Earth is currently entering a new glacial period, and orbital observations show that GAIA has indeed repopulated certain regions with lazurogened Pleistocene megafauna. However, this not thought to have nothing to do with the ideology of those earlier groups.
The Auld Limners reached their greatest extent during this time, which is known in Galactic History as the Auldlimnerian Epoch.