USGS Paleontology glossary Acritarch microscopic organic structure from any of a number of organisms; common during the Proterozoic. Adaptive radiation, evolutionary radiation the rapid expansion and diversification of a group of organisms as they fill unoccupied ecological nichesevolving into new species.
According to the Milankovitch theory, these factors cause a periodic cooling of Earth, with the coldest part in the cycle occurring about every 40, years. The main effect of the Milankovitch cycles is to change the contrast between the seasons, not the overall amount of solar heat Earth receives.
The result is less ice melting than accumulating, and glaciers build up. Milankovitch worked out the ideas of climatic cycles in the s and s, but it was not until the s that a sufficiently long and detailed chronology of the Quaternary temperature changes was worked out to test the theory adequately.
A problem with the theory is that these astronomical cycles have been in existence for many millions of years, but glaciation is a rare occurrence.
Astronomical cycles correlate with glacial and interglacial periods, and their transitions, within a long-term ice age but do not initiate these long-term ice ages. Atmospheric composition[ edit ] One theory holds that decreases in atmospheric CO 2an important greenhouse gasstarted the long-term cooling trend that eventually led to glaciation.
High CO2 contents correspond to warm interglacial periods, and low CO2 to glacial periods.
However, studies indicate that CO 2 may not be the primary cause of the interglacial-glacial transitions, but instead acts as a feedback. Plate tectonics and ocean current An important component in the development of long-term ice ages is the positions of the continents.
Throughout most of geologic timethe North Pole appears to have been in a broad, open ocean that allowed major ocean currents to move unabated. Equatorial waters flowed into the polar regions, warming them. This produced mild, uniform climates that persisted throughout most of geologic time.
This drift interlocked with the development of the Atlantic Oceantrending north-south, with the North Pole in the small, nearly landlocked basin of the Arctic Ocean. The Isthmus of Panama developed at a convergent plate margin about 3 million years ago, and further separated oceanic circulation, closing the last strait, outside the polar regions, that had connected the Pacific and Atlantic Oceans.
The most obvious effects are the spectacular mountain scenery and other continental landscapes fashioned both by glacial erosion and deposition instead of running water.
Entirely new landscapes covering millions of square kilometers were formed in a relatively short period of geologic time. In addition, the vast bodies of glacial ice affected Earth well beyond the glacier margins.
Directly or indirectly, the effects of glaciation were felt in every part of the world. Glacial lake A diagram of the formation of the Great Lakes The Quaternary glaciation created more lakes than all other geologic processes combined. The reason is that a continental glacier completely disrupts the preglacial drainage system.
The surface over which the glacier moved was scoured and eroded by the ice, leaving a myriad of closed, undrained depressions in the bedrock. These depressions filled with water and became lakes.Purpose.
This work is meant to provide a guide to the freshwater fishes of Iran.
There are no modern keys to this fauna, some available books are incomplete or cursory treatments or outdated, and the detailed and diverse scientific literature is widely scattered in time, languages and journals.
The following, inevitably incomplete, introductory glossary of terms and concepts links to other topics discussed elsewhere on this site, as well as including general topics of interest such as well-known prehistoric animals.
Nov 11, · The next ice age almost certainly will reach its peak in about 80, years, but debate persists about how soon it will begin, with the latest theory being that the human influence on the.
Sep 16, · I don’t pretend to be able to predict the obvious onset of the next glaciation, but under today’s ocean circulation conditions and orbital dynamics, we are 1,+ times more likely to be in a glaciation period within , years than to have runaway global warming.
Another scientific reason that can be used to support the idea that another glaciation will not occur within the next 10 million years is global warming.
Global warming has been an issue as the world has expanded and began using resources that are not as environmentally friendly as in the past%(5). Write a one-page paper on the likelihood of another extensive glaciation occurring within the next million years.
How about two million years or even 10 million years? 1.).