Conodonts, temperature and biodiversity
Sunday, 27. July 2008, 14:09:30
For the past 50 years oxygen isotopes in fossil marine carbonate shells like foraminfera or brachiopods have regularly been used to estimate ancient sea-surface temperature. This seems to work quite well for temperatures over the last 100 million years or so, but for various reasons doubt has recently arisen whether this type of thermometry is sufficiently reliable for periods as old as say 250 million years.
In a study published in the journal Science of 25. july 2008 Trotter et al. used a different global climate record determined by oxygen isotope analyses of conodonts from a period of around 488 to 416 million years ago (Ordovician-Silurian) .
Conodonts are extinct eel-like creatures. For many years, conodonts were known only from tooth-like microfossils, which occur commonly but always in isolation, and were not associated with any other fossil. Most of the conodont animal was soft-bodied, thus everything but the “teeth” were not suited for preservation under normal circumstances. Conodonts are small, ~0.1 to 3 mm long, These micro-fossils are composed of phosphate (apatite or calcium phosphate). They lived from Late Cambrian to Late Triassic and in this time they evolved rapidly, providing a fine stratigraphic resolution for the studied period. The phosphate minerals of conodont micro-fossils are more stable than carbonates of marine fossils. Conodont is by the way derived from Greek “cone-shaped” (konos + odont).
The researchers found that marine water at the beginning of the Ordovician (480 million years ago) was very warm (around 45°C), too warm for complex living organisms to develop. From then on a progressive ocean cooling of about 15°C took place over a period of 40 million until the ocean about 465 million years ago reached (sea-surface) temperatures comparable with those of today, around 30°C in the equatorial range. The temperature stayed around this for the next 15 million years, and the interesting thing is that the global change in climate might explain the explosion in marine biodiversity that took place 460 million years ago. The cooling of the oceans was coupled with atmospheric cooling, indicating that a global change in climate took place. The progressive ocean cooling coincided with an explosion in marine biomass and biodiversity (the number of genera and families jumped by a factor of three to four). This event took place during the Upper Ordovician, around 460 million years ago, when ocean temperatures became comparable to those of present day equatorial waters. Not only did marine animals diversify, but their range also spread to the seafloor, and the first coral reefs appeared.
At the end of Ordovician sea-surface temperatures dropped drastically and the so-called Great Ordovician Biodiversification Event (GOBE) was terminated with sudden and catastrophic extinctions during the latest Ordovician (Hirnantian), probably associated with rapid ice sheet growth at the South Palaeo-pole.
Reference:
Trotter et al, Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry, Science, 25 July 2008 (DOI: 10.1126/science.1155814)
• http://www.sciencemag.org/cgi/content/abstract/321/5888/550
• http://www.alphagalileo.org/index.cfm?_rss=1&fuseaction=readrelease&releaseid=531188
• http://www.scientificblogging.com/news_releases/marine_biodiversity_got_a_climate_change_boost
Maybe we have a tendency to stress negative events like mass extinctions, and forget telling about positive events like biodiversifation events - the GOBE is only one of several. The “Cambrian explosion” is the better known. Read for instance about evil or good volcanoes at Highly Allochtonous. Without life there would be no extinctions!
In a study published in the journal Science of 25. july 2008 Trotter et al. used a different global climate record determined by oxygen isotope analyses of conodonts from a period of around 488 to 416 million years ago (Ordovician-Silurian) .
Conodonts are extinct eel-like creatures. For many years, conodonts were known only from tooth-like microfossils, which occur commonly but always in isolation, and were not associated with any other fossil. Most of the conodont animal was soft-bodied, thus everything but the “teeth” were not suited for preservation under normal circumstances. Conodonts are small, ~0.1 to 3 mm long, These micro-fossils are composed of phosphate (apatite or calcium phosphate). They lived from Late Cambrian to Late Triassic and in this time they evolved rapidly, providing a fine stratigraphic resolution for the studied period. The phosphate minerals of conodont micro-fossils are more stable than carbonates of marine fossils. Conodont is by the way derived from Greek “cone-shaped” (konos + odont).The researchers found that marine water at the beginning of the Ordovician (480 million years ago) was very warm (around 45°C), too warm for complex living organisms to develop. From then on a progressive ocean cooling of about 15°C took place over a period of 40 million until the ocean about 465 million years ago reached (sea-surface) temperatures comparable with those of today, around 30°C in the equatorial range. The temperature stayed around this for the next 15 million years, and the interesting thing is that the global change in climate might explain the explosion in marine biodiversity that took place 460 million years ago. The cooling of the oceans was coupled with atmospheric cooling, indicating that a global change in climate took place. The progressive ocean cooling coincided with an explosion in marine biomass and biodiversity (the number of genera and families jumped by a factor of three to four). This event took place during the Upper Ordovician, around 460 million years ago, when ocean temperatures became comparable to those of present day equatorial waters. Not only did marine animals diversify, but their range also spread to the seafloor, and the first coral reefs appeared.
At the end of Ordovician sea-surface temperatures dropped drastically and the so-called Great Ordovician Biodiversification Event (GOBE) was terminated with sudden and catastrophic extinctions during the latest Ordovician (Hirnantian), probably associated with rapid ice sheet growth at the South Palaeo-pole.
Reference:
Trotter et al, Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry, Science, 25 July 2008 (DOI: 10.1126/science.1155814)
• http://www.sciencemag.org/cgi/content/abstract/321/5888/550
• http://www.alphagalileo.org/index.cfm?_rss=1&fuseaction=readrelease&releaseid=531188
• http://www.scientificblogging.com/news_releases/marine_biodiversity_got_a_climate_change_boost
Maybe we have a tendency to stress negative events like mass extinctions, and forget telling about positive events like biodiversifation events - the GOBE is only one of several. The “Cambrian explosion” is the better known. Read for instance about evil or good volcanoes at Highly Allochtonous. Without life there would be no extinctions!
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