What is one hypothesis for the mass extinction at the end of the cretaceous period?

Answer 1

The Permian-Triassic (P-Tr) mass extinction that marked the end of the Paleozoic Era is widely recognised as the greatest mass extinction in Earths history. It is known as the Great Dying. Up to 90% of all marine species and 60% of all land vertebrates became extinct. It was also the only known mass extinction of insects with 83% of all insect genera becoming extincted.

It was not just one continuous extinction event but rather came in up to 3 separate pulses.

There are many theories to the cause of the P-Tr extinction.

Climate change

About half way through the Permian Period approx 270 million years ago all the continents of Earth joined together to form the super continent Pangaea. This would have caused huge changes to the environments on earth. It is theorised the there was a super desert created in the interior of Pangaea.

Volcanic activity.

Around 260-250 million years ago there was 2 huge eruptions. The first was the Emeishan Traps in what is now China was the 1st and smaller of the 2. It happened about 260 million years ago and seemed to coincide with one of the extinction pulses known as the end-Guadalupian Pulse.

The second much larger eruption, the Siberian Traps coincides with the very last pulse about 251 million years ago.

Meteorite impact.

Evidence found in rocks from the P-Tr boundary has been found in Australia and Antarctica that suggest that Earth suffered a large impact event that happened about 251 million years ago. There have even been suggestions of possible craters such as the Bedout Structure off the coast of Australia or the Wilkes Land Crater in Antarctica.

There is a unusually high concentration of shocked quartz and rocks from the area seem to be unusually high in Iron, Nickle and Silicon which are common elements in asteroids. Recent reexamination of one sample from Antarctica however suggest that the quartz has not been shocked but has suffered plastic deformation which is common in volcanic activity.

Methane Hydrate Gasification.

Scientist world wide have found that there is a decrease in the ration between Carbon13 / Carbon12 in late Permian and early Triassic rocks. There are several possible causes for this but non of them can explain it fully.

Volcanism is one possible cause but it would have taken an eruption many times larger than any known.

A reduction in organic activity is another theory but studies of other similar events have left scientists to conclude that even if all the organic matter was buried in sedimentary rocks it would not explain the levels seen.

If there was a sudden drop in ocean levels exposure of organic rich sediments would be exposed to oxidisation. However scientist do not think that even this can explain the levels.

Another theory is that there was a break down in the oceanic currents and the deep oceans suffered a drop in oxygen known as anoxia or possibly a huge increase in levels of oxygen in the deep oceans called hyperoxia.

The only credible reason for the shift in ratios is the release of huge amounts of methane. Small microbes that generally live at the bottom of the sea produce methane Hydrates. Theses methane hydrates are methane molecules trapped in a cages of water molecules. This is normally trapped in the sediments Evidence that the Part Siberian Traps were actually a shallow sea at the time and the eruptions caused a huge releases of methane.

Sea Level Changes

The most biologically rich are of the ocean is in the shallow area of the continental crust. If the sea levels fell sufficiently it would destroy most of these habitats. This would explain the massive levels of extinction in marine life.

Anoxia

Evidence from the ratios of uranium/thorium found in Permian rocks from Greenland prove that at the end of the Permian the oxygen levels in the deep oceans dropped dramatically. This would have had devastating effects on life in the oceans.

Hydrogen Sulphide Emissions.

An anoxic event like the one described could have made sulpher reducing bacteria more dominant in our oceans. Vast amounts of hydrogen sulphide would have been produced as a consequence, poisoning both plants and animals and also decreasing ozone in the atmosphere thus increasing UV radiation.

This theory has some Merritt because it can explain the reduction in fauna that we find from the period.

Combination of events.

No one theory can really explain the extinction event fully. Scientists are starting to think that is was possibly a combination of some or all the theories mentioned.

Answer 2

The Permian-Triassic (P-Tr) mass extinction that marked the end of the Paleozoic Era is widely recognised as the greatest mass extinction in Earths history. It is known as the Great Dying. Up to 90% of all marine species and 60% of all land vertebrates became extinct. It was also the only known mass extinction of insects with 83% of all insect genera becoming extincted.

It was not just one continuous extinction event but rather came in up to 3 separate pulses.

There are many theories to the cause of the P-Tr extinction.

Climate change

About half way through the Permian Period approx 270 million years ago all the continents of Earth joined together to form the super continent Pangaea. This would have caused huge changes to the environments on earth. It is theorised the there was a super desert created in the interior of Pangaea.

Volcanic activity.

Around 260-250 million years ago there was 2 huge eruptions. The first was the Emeishan Traps in what is now China was the 1st and smaller of the 2. It happened about 260 million years ago and seemed to coincide with one of the extinction pulses known as the end-Guadalupian Pulse.

The second much larger eruption, the Siberian Traps coincides with the very last pulse about 251 million years ago.

Meteorite impact.

Evidence found in rocks from the P-Tr boundary has been found in Australia and Antarctica that suggest that Earth suffered a large impact event that happened about 251 million years ago. There have even been suggestions of possible craters such as the Bedout Structure off the coast of Australia or the Wilkes Land Crater in Antarctica.

There is a unusually high concentration of shocked quartz and rocks from the area seem to be unusually high in Iron, Nickle and Silicon which are common elements in asteroids. Recent reexamination of one sample from Antarctica however suggest that the quartz has not been shocked but has suffered plastic deformation which is common in volcanic activity.

Methane Hydrate Gasification.

Scientist world wide have found that there is a decrease in the ration between Carbon13 / Carbon12 in late Permian and early Triassic rocks. There are several possible causes for this but non of them can explain it fully.

Volcanism is one possible cause but it would have taken an eruption many times larger than any known.

A reduction in organic activity is another theory but studies of other similar events have left scientists to conclude that even if all the organic matter was buried in sedimentary rocks it would not explain the levels seen.

If there was a sudden drop in ocean levels exposure of organic rich sediments would be exposed to oxidisation. However scientist do not think that even this can explain the levels.

Another theory is that there was a break down in the oceanic currents and the deep oceans suffered a drop in oxygen known as anoxia or possibly a huge increase in levels of oxygen in the deep oceans called hyperoxia.

The only credible reason for the shift in ratios is the release of huge amounts of methane. Small microbes that generally live at the bottom of the sea produce methane Hydrates. Theses methane hydrates are methane molecules trapped in a cages of water molecules. This is normally trapped in the sediments Evidence that the Part Siberian Traps were actually a shallow sea at the time and the eruptions caused a huge releases of methane.

Sea Level Changes

The most biologically rich are of the ocean is in the shallow area of the continental crust. If the sea levels fell sufficiently it would destroy most of these habitats. This would explain the massive levels of extinction in marine life.

Anoxia

Evidence from the ratios of uranium/thorium found in Permian rocks from Greenland prove that at the end of the Permian the oxygen levels in the deep oceans dropped dramatically. This would have had devastating effects on life in the oceans.

Hydrogen Sulphide Emissions.

An anoxic event like the one described could have made sulpher reducing bacteria more dominant in our oceans. Vast amounts of hydrogen sulphide would have been produced as a consequence, poisoning both plants and animals and also decreasing ozone in the atmosphere thus increasing UV radiation.

This theory has some Merritt because it can explain the reduction in fauna that we find from the period.

Combination of events.

No one theory can really explain the extinction event fully. Scientists are starting to think that is was possibly a combination of some or all the theories mentioned.

Answer 3

They hypothesize that this mass extinction occurred when an object from space struck earth.