CLimate change as a selection pressure: Permian- Triassic Extinction
Life and climate pre-extinction -
At the end of the Permian, and the beginning of the Triassic eras, 252 million years ago one of the largest mass extinctions to ever take place in the history of the planet occurred. This wiped out 83%[1] of all Genus groups that were living on the Earth. The volatile climate during this time greatly contributed to the loss of many species that could not cope with the new and constantly changing conditions of this time. At the time ‘Great Dying’ (the epithet that accompanies this period of time) the earth had one main supercontinent; Pangaea. The large size of Pangaea caused extremes in temperatures, as happens today in the centres of large landmasses, for example today in areas such as Kiev in Ukraine, as the sea moderates the temperature in both summer and winter by cooling and warming slower than the land. The north experienced high temperatures and fluctuations in rainfall, whereas the south was cold and arid. [2]
Causes of extinction -
Increasing volcanic activity from the ‘Siberian traps’ (a volcanic region in Siberia) at this time added to carbon dioxide levels in the atmosphere causing a green house gas effect. Although it has been suggested that life was struggling due to the harsh environment beforehand, additional changes may have been the tipping point causing the extinction. Suggested levels of lava flow from the Siberian traps are around 1.5 million cubic kilometers [3]. Not only would this amount of lava destroyed many habitats and surrounding areas, but the dust and dirt would have had resounding effects spreading overa large area, not to mention the huge carbon dioxide releases insulating the planet and raising temperatures.[4] In addition to a rise in volcanicity, the Gondawa (an area in southern Pangaea) ice caps were melting (rise in CO2 levels contributed to this) raising sea levels.[5] Sedimentary evidence however suggests cooling in this period. Glacial deposits and thick sand dunes have provided data for a cool dry climate. The volcanic gasses could have actually cooled the climate. The contradictory evidence of heating and cooling has led scientists to believe that there were sharp and rapid rises and falls in temperature actually occurred during the extinction period.
Life and climate after the extinction event -
Species were unable to keep up with this ultimately causing mass extinction.[4] The increase in temperature would have lowered the metabolic rate of creatures and disrupted the formation of some species carbonate shells and internal structures.[6] In fact, 96%[7] of all marine species (whose skeletons were largely made from carbonates) became extinct. The high CO2 levels would have also been toxic, and quick successive changing temperatures also altered salinity levels in seawaters. Marine creatures unable to adapt would have succumbed to selective extinction. [4] Calcareous sponges, rugose and tabulate corals, calciate brachiopods, bryozoans, and echinoderms were some of the species extinct, largely because of the effects on their structure formation. Other marine life, for example the sea anemone whose structure is not calcareous evolved and adapted to what we now know as modern corals.[8] Trilobites also became extinct, creating an important fossil index for the lower Paleozoic. [5]
Regarding land species, roughly 60 to 70% of labyrinthodont amphibians, sauropsid and therapsid families became extinct. After the extinction the Lystrosaurus (a therapsid) made up 90% of all early Triassic land vertebrate. Archosaurs then began to replace the therapsids, and these went on to evolve into the dinosaurs.[9] This extinction period was also the only known mass extinction of the insects too. It seems that no groups of species could escape the changes occurring
At the end of the Permian, and the beginning of the Triassic eras, 252 million years ago one of the largest mass extinctions to ever take place in the history of the planet occurred. This wiped out 83%[1] of all Genus groups that were living on the Earth. The volatile climate during this time greatly contributed to the loss of many species that could not cope with the new and constantly changing conditions of this time. At the time ‘Great Dying’ (the epithet that accompanies this period of time) the earth had one main supercontinent; Pangaea. The large size of Pangaea caused extremes in temperatures, as happens today in the centres of large landmasses, for example today in areas such as Kiev in Ukraine, as the sea moderates the temperature in both summer and winter by cooling and warming slower than the land. The north experienced high temperatures and fluctuations in rainfall, whereas the south was cold and arid. [2]
Causes of extinction -
Increasing volcanic activity from the ‘Siberian traps’ (a volcanic region in Siberia) at this time added to carbon dioxide levels in the atmosphere causing a green house gas effect. Although it has been suggested that life was struggling due to the harsh environment beforehand, additional changes may have been the tipping point causing the extinction. Suggested levels of lava flow from the Siberian traps are around 1.5 million cubic kilometers [3]. Not only would this amount of lava destroyed many habitats and surrounding areas, but the dust and dirt would have had resounding effects spreading overa large area, not to mention the huge carbon dioxide releases insulating the planet and raising temperatures.[4] In addition to a rise in volcanicity, the Gondawa (an area in southern Pangaea) ice caps were melting (rise in CO2 levels contributed to this) raising sea levels.[5] Sedimentary evidence however suggests cooling in this period. Glacial deposits and thick sand dunes have provided data for a cool dry climate. The volcanic gasses could have actually cooled the climate. The contradictory evidence of heating and cooling has led scientists to believe that there were sharp and rapid rises and falls in temperature actually occurred during the extinction period.
Life and climate after the extinction event -
Species were unable to keep up with this ultimately causing mass extinction.[4] The increase in temperature would have lowered the metabolic rate of creatures and disrupted the formation of some species carbonate shells and internal structures.[6] In fact, 96%[7] of all marine species (whose skeletons were largely made from carbonates) became extinct. The high CO2 levels would have also been toxic, and quick successive changing temperatures also altered salinity levels in seawaters. Marine creatures unable to adapt would have succumbed to selective extinction. [4] Calcareous sponges, rugose and tabulate corals, calciate brachiopods, bryozoans, and echinoderms were some of the species extinct, largely because of the effects on their structure formation. Other marine life, for example the sea anemone whose structure is not calcareous evolved and adapted to what we now know as modern corals.[8] Trilobites also became extinct, creating an important fossil index for the lower Paleozoic. [5]
Regarding land species, roughly 60 to 70% of labyrinthodont amphibians, sauropsid and therapsid families became extinct. After the extinction the Lystrosaurus (a therapsid) made up 90% of all early Triassic land vertebrate. Archosaurs then began to replace the therapsids, and these went on to evolve into the dinosaurs.[9] This extinction period was also the only known mass extinction of the insects too. It seems that no groups of species could escape the changes occurring
References:
[1] Benton M J (2005). When life nearly died: the greatest mass extinction of all time. London: Thames & Hudson.
[2] http://science.nationalgeographic.co.uk/science/prehistoric-world/permian/
[3] http://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction/
[4]http://palaeo.gly.bris.ac.uk/palaeofiles/permian/climate.html:
[5] UCL GEOL 1013 part 8, the Paleozoic – Graham Shields
[6] Knoll, A H. Bambach, R K. Canfield, D E. and Grotzinger, J P.Science, vol. 273, pp452 - 457, (1996)
[7] Benton M J (2005). When life nearly died: the greatest mass extinction of all time. London: Thames & Hudson
[8] Knoll, A.H., Bambach, R.K., Payne, J.L., Pruss, S., and Fischer, W.W. (2007). "Paleophysiology and end-Permian mass extinction". Earth and Planetary Science Letters 256 (3–4): 295–313.
[9] Tanner LH, Lucas SG & Chapman MG (2004). "Assessing the record and causes of Late Triassic extinctions" Earth-Science Reviews 65 (1–2): 103–139
http://www.rareresource.com/pho_lystrosaurus.htm
http://www.fossilicious.com/Brachiopod-Licharewia-pr-17111.html
[1] Benton M J (2005). When life nearly died: the greatest mass extinction of all time. London: Thames & Hudson.
[2] http://science.nationalgeographic.co.uk/science/prehistoric-world/permian/
[3] http://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction/
[4]http://palaeo.gly.bris.ac.uk/palaeofiles/permian/climate.html:
[5] UCL GEOL 1013 part 8, the Paleozoic – Graham Shields
[6] Knoll, A H. Bambach, R K. Canfield, D E. and Grotzinger, J P.Science, vol. 273, pp452 - 457, (1996)
[7] Benton M J (2005). When life nearly died: the greatest mass extinction of all time. London: Thames & Hudson
[8] Knoll, A.H., Bambach, R.K., Payne, J.L., Pruss, S., and Fischer, W.W. (2007). "Paleophysiology and end-Permian mass extinction". Earth and Planetary Science Letters 256 (3–4): 295–313.
[9] Tanner LH, Lucas SG & Chapman MG (2004). "Assessing the record and causes of Late Triassic extinctions" Earth-Science Reviews 65 (1–2): 103–139
http://www.rareresource.com/pho_lystrosaurus.htm
http://www.fossilicious.com/Brachiopod-Licharewia-pr-17111.html