daurangir
08-14-2008, 01:31 PM
Climatic variation and change through geologic time
The Earth system has undergone dramatic changes throughout its 4.5-billion-year history. These have included climatic changes diverse in mechanisms, magnitudes, rates, and consequences. Many of these past changes are obscure and controversial, and some have been discovered only recently. Nevertheless, the history of life has been strongly influenced by these changes, some of which radically altered the course of evolution. Life itself is implicated as a causative agent of some of these changes, as the processes of photosynthesis and respiration have largely shaped the chemistry of Earth’s atmosphere, oceans, and sediments.
Climatic variation and change through geologic time » Cenozoic climates
The [/URL][URL="http://www.britannica.com/EBchecked/topic/101936/Cenozoic-Era"]Cenozoic Era (http://www.khyberwatch.com/forums/), encompassing the 65 million years that have elapsed since the mass extinction event marking the end of the Cretaceous Period (http://www.britannica.com/EBchecked/topic/142729/Cretaceous-Period), has a broad range of climatic variation characterized by alternating intervals of global warming and cooling. Earth has experienced both extreme warmth and extreme cold during this period. These changes have been driven by tectonic forces, which have altered the positions and elevations of the continents as well as ocean passages and bathymetry. Feedbacks between different components of the Earth system (atmosphere, biosphere, lithosphere, cryosphere, and oceans in the hydrosphere) are being increasingly recognized as influences of global and regional climate. In particular, atmospheric concentrations of carbon dioxide have varied substantially during the Cenozoic for reasons that are poorly understood, though its fluctuation must have involved feedbacks between Earth’s spheres.
Orbital forcing is also evident in the Cenozoic, although, when compared on such a vast era-level timescale, orbital variations can be seen as oscillations against a slowly changing backdrop of lower-frequency climatic trends. Descriptions of the orbital variations have evolved according to the growing understanding of tectonic and biogeochemical changes. A pattern emerging from recent paleoclimatologic studies suggests that the climatic effects of eccentricity, precession, and axial tilt have been amplified during cool phases of the Cenozoic, whereas they have been dampened during warm phases.
The Earth system has undergone dramatic changes throughout its 4.5-billion-year history. These have included climatic changes diverse in mechanisms, magnitudes, rates, and consequences. Many of these past changes are obscure and controversial, and some have been discovered only recently. Nevertheless, the history of life has been strongly influenced by these changes, some of which radically altered the course of evolution. Life itself is implicated as a causative agent of some of these changes, as the processes of photosynthesis and respiration have largely shaped the chemistry of Earth’s atmosphere, oceans, and sediments.
Climatic variation and change through geologic time » Cenozoic climates
The [/URL][URL="http://www.britannica.com/EBchecked/topic/101936/Cenozoic-Era"]Cenozoic Era (http://www.khyberwatch.com/forums/), encompassing the 65 million years that have elapsed since the mass extinction event marking the end of the Cretaceous Period (http://www.britannica.com/EBchecked/topic/142729/Cretaceous-Period), has a broad range of climatic variation characterized by alternating intervals of global warming and cooling. Earth has experienced both extreme warmth and extreme cold during this period. These changes have been driven by tectonic forces, which have altered the positions and elevations of the continents as well as ocean passages and bathymetry. Feedbacks between different components of the Earth system (atmosphere, biosphere, lithosphere, cryosphere, and oceans in the hydrosphere) are being increasingly recognized as influences of global and regional climate. In particular, atmospheric concentrations of carbon dioxide have varied substantially during the Cenozoic for reasons that are poorly understood, though its fluctuation must have involved feedbacks between Earth’s spheres.
Orbital forcing is also evident in the Cenozoic, although, when compared on such a vast era-level timescale, orbital variations can be seen as oscillations against a slowly changing backdrop of lower-frequency climatic trends. Descriptions of the orbital variations have evolved according to the growing understanding of tectonic and biogeochemical changes. A pattern emerging from recent paleoclimatologic studies suggests that the climatic effects of eccentricity, precession, and axial tilt have been amplified during cool phases of the Cenozoic, whereas they have been dampened during warm phases.