Climate Science: Investigating Climatic and Environmental Processes
Beyond 100,000 Years (+10⁵ Years)
In 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 lithosphere-- 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. (Alvarez, 1980).

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, 1998). See Rocks 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 up.

While the 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.

Gondwana and the South Pole

Numbers reflect millions of years.

Note that modern-day continents are outlined, not the actual land masses associated with Gondwana.

FORCING FACTORS




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 cycle.