From Palaeos.com:

The term Pleistocene ("most recent") was coined by external link Charles Lyell in 1839, on the basis of a section of type strata in eastern Sicily, according to the proportion of extinct to living species of mollusk shells in the sediment. Strata with 90 to 100% present day species were designated Pleistocene. Clearly this is a somewhat arbitrary arrangement, and in any cases many strata do not contain mollusk shells.

The present definition of the Pleistocene is based on radiometric dating of 1.6 million years or more recent, the presence of cooler water mollusks and foraminifers, the absence of marine micro-organisms called discoasters, and on land the fossil remains of modern horses and true elephants (in the past more widespread than they are today).

Catchy Caption of the Day

Former FBI Deputy Director W. Mark Felt who now claims to be Woodward and Bernstein's "Deep Throat."

See? I told you it wasn't someone named "Monica."

(AP Photo/Ben Margo )