“Being Milutin Milankovitch” Or “From Millennia to Hours: The Decreasing Scales of the Orbital Theory of Multin Milankovitch” Adapted from Dr. Randy Cerveny Presidential Professor, ASU

Milankovitch Theory Milutin Milankovitch, Serbian mathematician and astronomer In 1938, hand-computed insolation at 65° N based on orbital variations for two 6-month seasons (summer & winter)

Milankovitch Theory He computed variations in three primary orbital parameters: Tilt Eccentricity Precession of the Longitude of Perihelion in relation to the Moving Equinox (“Precession”)

Milankovitch Theory Tilt The variations in the axial tilt of the Earth. This orbital component has a cycle of 42,000 years for the Earth to shift from an axial tilt of 22.1° to 24.5° and back

Milankovitch Theory Eccentricity The variations associated with the shape of the Earth’s orbit (oblique to circular) The primary cycle of eccentricity is 93,000 years with a secondary cycle at 400,000 years.

Milankovitch Theory Precession Most complex of the three mechanisms. Refers to the season in which perihelion is occurring as a function of the orientation (or “wobble”) of the Earth’s axis

Milankovitch Theory Current Precession Earth’s perihelion in early January given the current axial orientation towards the star Polaris But 11,000 years from now, perihelion will occur in July The primary cycles for precession are 19,000 and 23,000 years.

Two huge problems in gaining acceptance for his theory No reliably-dated evidence Unknown which dates were the most important Theory put on back burner until more evidence gathered...

CLIMAP & the ocean corers International project in mid-1970s Help better understand when the last ice age occurred Includes two important research thrusts First, a chronology of past climates was begun using deep-sea marine cores.

Hays, Imbrie & Shackleton: Pacemaker to the Ice Ages Spectral analyses of cores suggested existence of distinct correlation. Closely matched the cycles computed by Milankovitch for the Earth’s three orbital mechanisms.

Producer vs. consumer? Remember a producer is a organism that makes a certain chemical. A consumer is an organism or thing that uses a certain chemical.