Geography Reference
In-Depth Information
important. First, in the 1930s, Milutin Milankovitch, a Serbian
applied mathematician, developed the 'astronomical theory',
which successfully explains the regular climatic changes
associated with glacials and interglacials - the 'pulsebeat' of the
Ice Age (see box).
The astronomical theory of climatic change
This mathematical theory, also known as the 'Milankovitch
theory', accounts for the regular, long-term variations of
climate that produced glacials and interglacials over the
Quaternary period. The theory was disputed during Milutin
Milankovitch's lifetime but was later fully tested and is now
widely accepted. It predicts the quantity and distribution of
solar radiation received at the Earth's surface in response
to regular variations in the distance of the Earth from the
sun. This depends on three so-called orbital parameters: the
precession of the equinoxes, which varies with a periodicity of
about 21,000 years; the obliquity of the ecliptic, which varies
with a periodicity of about 41,000 years; and the eccentricity
of the orbit, the periodicity of which is about 100,000 years.
These orbital variations can be envisaged, respectively, as
measures of the 'wobble' and 'tilt' of the Earth about its
axis and the 'stretch' of the Earth's orbit (the extent that
the elliptical orbit departs from a circle). The three orbital
parameters combine to determine the pattern and timing of
glacials and interglacials: the former correspond with times
of minimum solar radiation receipt; the intervening intervals
are the interglacials.
The fi rst decisive test of the astronomical theory utilized data
from marine sediment cores, which retrieved the material
that had slowly accumulated on the deep ocean fl oor during
successive glacials and interglacials. Specifi cally, the oxygen
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