Just imagine what the first human beings experienced when they migrated across an ice and land bridge from Asia to Alaska almost 11,000 years ago. Ice from the last ice age was retreating from northern United States. Woolly mammoths roamed the countryside. Several weeks ago a friend encouraged me to attend a lecture at the Roger Tory Peterson Institute which I did, but became distracted and drawn to the unrelated exhibit displaying the skull and tusks of the Randolph, N.Y., mammoth. This skull, not a fossil but a real bone, was discovered in 1934 during excavation for the existing fish hatchery. The exhibit provided a timeline of Earth's history describing a series of ice ages over the last 2.6 million years that covered much of North America and Europe with ice a mile thick. The most recent ice age lasted 12,000 to 25,000 years. Geologists found evidence that ice ages occurred at regular long intervals over Earth's history and, more specifically, over 10 ice ages developed in the last 2 million years. I set out to discover how drastic climate changes could occur.