Astronomical Cycles Cause The Ice Ages

Astronomical Cycles Cause The Ice Ages

. The advance and retreat of glaciers are controlled by changes in the Earth’s orbital shape or eccentricity, and variations in its axial tilt and wobble. They alter the angles and distances from which solar radiation reaches Earth, and therefore change the amount and distribution of sunlight on our planet. The global ebb and flow of ice is inferred from the presence of lighter and heavier forms of oxygen, called isotopes, in the fossilized shells of tiny marine animals found in deep-sea sediments. During glaciations, the shells are enriched with oxygen-18 because oxygen-16, a lighter form, is trapped in glacial ice. The relative abundance of oxygen 18 and oxygen 16 (top) is compared with periodic 41,000-year variations in the tilt of the Earth’s axis (middle) and in the shape, or eccentricity – longer 100,000-year variation, and wobble, or precession, of the Earth’s orbit – shorter 23,000-year variation (bottom).

Copyright 2010, Professor Kenneth R. Lang, Tufts University