Climatic and Environmental Processes
Beyond 100,000 Years (+105
general, much more is known about the Earth's history in the past
500 million years than the prior four billion years. In examining
past climate changes, including intervals of glaciation and changes
in the atmospheric composition, scientists have considered how plate
tectonics-- interactions caused by the movement of lithospheric
plates- have impacted the climate system.
the rigid outer shell of the Earth-- is now broken into a dozen
major tectonic plates that over the past hundreds of millions of
years have migrated around the planet. Using paleomagnetic data,
scientists have been able to reconstruct where the various plates
and continents were located at different times in the past.
The figure to the left shows estimates of sea level over the course
of more than half a billion years of geologic history. The causes
of such changes in sea level are complex and are not always directly
correlated with changes in global temperature, but generally higher
sea levels reflect warmer temperatures. For example, 100 million
years ago, the Earth's temperature was 20° - 40° Celsius
warmer (or 36 ° - 72 ° F) in the polar regions, although
only a few degrees warmer around the equator. Evidence suggests
that during warm Cretaceous periods, levels of atmospheric carbon
dioxide were high. (Barron, et.
al., 1985.) Models indicate that carbon dioxide may have been
four to six times the pre-industrial levels. (Otto-Bliesner,
et. Al., 2001.)
An abrupt event 65 million years ago thought by many to be caused
by the impact of a asteroid hitting near present day Yucatan, Mexico,
has become known as the KT Boundary or Cretaceous-Tertiary mass
extinction event, which caused cooling and perhaps other environmental
factors that led to the extinction of 70% of the species and 40%
of all genera living at the time, ending the age of the dinosaurs.
The largest mass extinction occurred about 251 million years ago
at the end of the Permian, with an estimated 85% of marine species
and 70% of terrestrial vertebrate genera becoming extinct (Bowring,
Reveal Details of Mass Extinctions from more on this and other
mass extinctions and abrupt climate changes.
In the figure below, the ancient supercontinent of Gondwana, which
was comprised of modern day Antarctica, Africa, Arabia, Australia,
South America and India, is shown as it slowly moved over the South
Pole between 500 and 250 million years ago. About 260 million years
ago Gondwana collided with other land masses, forming Pangaea, a
giant supercontinent. (Ruddiman,
2001 ). About 180 million years ago, Pangaea started to break
locations of the continents would have had some impact on the global
climate system, changing surface albedo and altering ocean currents,
much of the climate research work being conducted on long term variability
has focused on carbon dioxide and how it is removed from the atmosphere.
and the South Pole
Numbers reflect millions
Note that modern-day continents are outlined, not the actual land
masses associated with Gondwana.
Tectonic processes that influence
climate system variability include plate motion, changes in continental
geography, mountain building and erosion, the production and subduction
of seafloor crust and related changes in bio-geo-chemical cycles,
particularly the carbon