What a presumptuous, anthropocentric category. The Holocene - the age of humans. Well, O.K. But the GEOLOGIC epoch of humans??? Is it something which deserves the same status as the Pliocene, Maastrichtian, Kimmerigian.....
In his new book, Heavan and Earth, Ian Plimer puts the timing into geologic perspective: The Holocene began approx. 11,500 yrs ago at the end of the Younger Dryas cooling and the beginning of modern human culture/civilisation. He mentions some geologic and climatologic changes, but from a real geologic perspective, nothing near the changes wrought by the termination of the last glacial maximum - so why the new epoch? The Younger Dryas was just a blip in the generally increasing temperatures since the beginning of the current interglacial which has continued to the present. The rise in temperature has been nothing near the rise in the previous interglacial, which was still considered part of the Pleistocene.
OK - so what about the extinction of megafauna - yes. North America lost proboscidae, horses, camels rhinoceros and other mammalian megafaulna - but those orders did not become extinct globally - and only some species became extinct. So why is this different than other epochs?
It can't be the presence of humans, as we were around as anatomicalliy modern humans for at least 100,000 years prior to the Holocene. It can't be the erosive force we humans have visited on the surface of the Earth - great as that is. Our erosive capacity is as nothing compared with the work done by the continental glaciers of the previous glacial maxima.
The Pleistocene is characterized as the recent glacial epoch - a time when there have been numerous glacial advances and retreats, punctuated by four major pulses. Past interglacials were warmer than the currnet one. We are right on the cusp of the average time of the end of past intergalcials. We still have sea ice and continental ice sheets, which are greater in extent than in previous interglacials. So why should we conclude we are out of the Pleistocene?
I am unconvinced. Professionally, I hold out for remaining in the Pleistocene with the Holocene as the next in a series of interglacials,all within the larger Pleistocene Epoch.
Now if AGW turns out to be real and human civilsation does end up melting all the glaciers and continental ice sheets and humans are the cause of the end of the global cooling which has dominated for 35 million years, then we can say we are out of the Pleistocene. Most unlikely, but that is another topic.