An Intriguing Explanation of Earth’s Glacial-Interglacial Cycles
Ice cores from Antarctica and Greenland have provided enormous insight into Earth’s climate over the past 800,000 years; in 2017 a deeper ice core may soon provide additional information, dating back 2.7 million years.
Ice cores are drilled in areas free of glaciers — meaning that snow has fallen and become compacted century after century. Ice cores reveal clues about past climate periods, specifically implications of global temperatures, combined with atmospheric CO2and O2 levels (bubbles trapped in the ice).
From these ice cores we know Earth’s climate has been cyclical. Milankovitch cycles, named in honor of the 1920s discoverer, a Serbian physicist/astronomer, comprise Glacial Periods of about 100,000 years interspersed with Interglacial Periods of about 10,000 years; additional warming and cooling episodes occur, inside these two major Periods. What has remained a mystery — is why these cycles occur with relative regularity.
Milankovitch postulated these cycles are caused by variations in: precession(change in orientation of Earth’s rotational axis, relative to its previous rotational orientation — best exemplified by precession of a child’s spinning top); eccentricity (amount by which Earth’s orbit around the sun deviates from a perfect circle); and axial tilt (angle between Earth’s rotational axis and orbital axis). These three entities are also influenced by gravitational pull of other planets, especially Jupiter because of its large mass.