The Pleistocene Epoch, commonly known as the Ice Age, began 2 million years ago (MYA). Four major glacial advances occurred during this Epoch, separated by warm interglacial periods; most climatologists believe that the Holocene, which began 10,000 years ago and continues today, is just another interglacial episode and that glaciation will redevelop within 10-15,000 years. More than an era of glaciers and Ice Age fauna, the Pleistocene witnessed significant volcanic activity and the final stages of human evolution; the role that volcanism played in the climate swings of the Pleistocene (and thus in the rise of humans) remains a point of controversy.
At the beginning of the Pleistocene, the first and major eruption of the Yellowstone Caldera occurred, Mt. Kilimanjaro (consisting of three volcanoes) rose along the African Rift and the San Francisco Peaks formed in the volcanic field of northern Arizona. At the same time, Homo erectus appeared in Africa; equipped with precise hand function and a pelvis that favored upright posture, he was the first hominid to use fire and spread to southeast Asia by 1.8 MYA. Today's major Cascade volcanoes began to form 1.6 MYA, the second eruption of Yellowstone occurred 1.2 MYA and the Valles Caldera of New Mexico's Jemez Mountains erupted 1.1 MYA.
Mauna Loa, the largest volcano on Earth today, first erupted 700 thousand years ago (TYA), followed by the third eruption of Yellowstone (600 TYA) and Mt. Ranier's first eruption (500 TYA). Homo heidelburgensis appeared in Africa 200 TYA; those that spread northward into Eurasia gave rise to the Neanderthals while those remaining in Africa, cut off and molded by drought, evolved into Homo sapiens (125 TYA). Finally, humans were nearly wiped out by the massive eruption of Toba (on Sumatra, 74 TYA); those that survived (perhaps as few as 10,000) have since colonized the globe and, in the process, triggered the demise of Neanderthals by 30 TYA.
