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Offline wanchung

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Evolution and extinction theory
« on: 07/02/2011 03:41:09 »
Evolution and extinction

By Wan-Jiung Hu

Extinction is a major nature selection process. It is a major driven force for evolution. However, the underlying reason for extinctions are not well understood. There are five massive extinctions in earth history. In addition, there are total twenty-three minor extinction events in earth history. The most famous massive extinction event is the KT extinction event. In this last massive extinction, all the dinosaurs died during this tragedy. A well known theory to explain the KT extinction event is comet or asteroid theory. Researchers believed that an asteroid or comet hit our earth during K-T period. The KT impact created dramatic global climate change and let animals and plants disappeared. However, this theory can only explain one extinction event and it is wrong. It cannot explain the other four massive extinction or other minor extinction events. There are no evidences showing that other asteroids or comets hit our earth to cause the other extinction events. We need a common mechanism to explain why there are repeated extinction events on earth. In addition, there are several defects in the KT impact theory. We will discuss this in the later paragraphs.

Here, I propose a new mechanism for all the extinction events. The reasons for these major and minor extinction events are due to Milankovitch cycle. Milankovitch cycle was proposed to explain the glaciation periods of earth. Our earth is undergoing global climate changes due to following reasons. 1. The eccentricity of orbit that our earth is rotating around the sun. 2. The axis tilt of earth (obliquity) when it is affected by the sun. 3. The apsidal and axial procession of our earth when it is around the sun. 4. The orbital inclination. Combining the above reasons, our earth is undergoing extremely hot or cold periods. During the cold periods, the glaciations happen. Thus, I propose here that extremely cold or hot periods on our earth are the major reasons for massive or minor extinction events.   

There are five massive extinctions (The Big Five) in earth history: 1. Ordovician-Silurian extinction event 2. Late Devonian extinction event 3. Permian-Triassic extinction event 4.Triassic-Jurassic extinction event 5. Cretaceous-Tertiary extinction event. The first massive extinction event is Ordovician-Silurian extinction happened in 440-450 Ma. During this extinction event, two main event phases killed 27% of all families and 57% of all genera. Many scientists rank this event as the second largest extinction event in earth history. The second massive extinction event is Late Devonian extinction happened in 360-375 Ma. This event lasted perhaps 20 MY, and it killed 19% of all families and 50% of all genera. The third massive extinction event is Permian-Triassic extinction happened in 251 Ma. This extinction event is called “Great Dying” which is the largest extinction on earth. It killed 57% of all families and 83% of all genera (53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species). The fourth massive extinction event is Triassic-Jurassic extinction happened in 205 Ma. This event killed 23% of all families and 48% of all genera(20% of marine families and 55% of marine genera). Most non-dinosaurian archosaurs, mot therapsids, and most of the large amphibians were eliminated, leaving dinosaurs with little terrestrial competition. The most recent massive extinction event is Cretaceous-Tertiary extinction happened in 70-65 Ma. It killed about 17% of all families, 50% of all genera, and 75% of all species. It ended the reign of dinosaurs and opened the way for mammals and birds to become dominant land vertebrates.

There are totally twenty-three extinction events on earth. Thus, these extinctions repeatedly happen. Despite of the well known asteroid/comet impact theory, we still cannot explain why there are so many extinction events. We don’t have any evidences show that a lot of asteroids/comets hit earth several times to cause these extinctions. We need a common cause to explain all the extinction events. Thus, I will list all the possible explanations first, and then I will deduct why Milankovitch cycle is the actual cause of these extinction events.


 

Offline wanchung

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Evolution and extinction theory
« Reply #1 on: 07/02/2011 03:41:59 »
The first explanation for extinction events is volcano eruption.   This theory suggested that massive volcano eruption during ancient times cause severe environment disturbance and cause major or minor extinctions. There are short term and long term environmental impact after volcano eruption. The short term effect is global cooling. The sulfur aerosol from volcano eruption will form SO2 gas in atmosphere. Sulfur aerosol will then absorb sunlight and cause earth surface temperature dropping. However, this effect is only transient. Because SO2 will be easily washed out by rain to produce acidic rain, the global cooling can only maintain for several months to ten years. In addition, current observation of global cooling effect induced by sulfur aerosol is only 0.5-0.8。C dropping. Thus, this transient mild effect due to sulfur aerosol is unlikely to cause severe extinction events. The long term effect of volcano eruption is global warming. Theorists suggested that volcano eruption can release a lot of CO2 which can cause green house effect. CO2 cannot be easily washed out by rain and it can stay in the atmosphere for fifty to two hundreds years. Among all big five extinction event, the Triassic-Jurassic boundary is the only event which is associated with global warming. This event happened in 205 Ma. Many researchers proposed the largest volcano on earth-Central Atlantic Magmatic Province (CAMP) eruption caused this massive extinction.  However, a recent study showed that CO2 concentration is quite stable as 250 ppm during the Triassic-Jurassic boundary.  If volcano eruption caused Triassic-Jurassic extinction, the atmosphere CO2 concentration should reach 3000-4000 ppm. (ln[CO2]’/[CO2]=kΔT, k=0.37)Massive extinction event can only occur if the global temperature increases 6-7 。C due to 3000-4000 ppm atmosphere CO2. In a study, it is estimated that CAMP eruption could release 1017 mole CO2 from 3*106 dusts due to the size of CAMP.  However, 1017 mole CO2 can also increase atmosphere CO2 to 200~300 ppm. Thus, CAMP eruption is unlikely the cause of TJ extinction. The duration of Triassic-Jurassic extinction is relatively short (~10000 years) compared to other major extinctions. However, 10000 years are still longer than the half life of atmosphere CO2 for 50-200 years. Now, we only observe the global cooling effect caused by volcano released sulfur aerosol. We never observe the global warming effect caused by volcano CO2 emission. In a recent study, carbon isotopes of lipids (n-alkanes) derived from leaf wax and lignin, and total organic carbon from two sections of lake sediments interbedded with the CAMP in the eastern North America have shown carbon isotope excursions similar to those found in the mostly marine St. Audrie’s Bay section in England.  The negative carbon excursion could be due to massive organism extinction with increased burial and decreased productivity. It is not a strong evidence for CAMP eruption. In addition, the Os187/Os188 ratio and the Sr87/Sr86 are decreased during TJ boundary. The non-radiogenic Os188 and Sr86 should be increased due to volcano eruption such as CAMP eruption.  We can say CAMP did erupt during Triassic-Jurassic period. However, CAMP eruption was postdated in 199-201 Ma after Triassic-Jurassic extinction in 205 Ma. Volcano was not the reason. Another two massive extinction events (End-Permian and End-Guadalupian) are also suggested to be related to the volcano eruptions. However, global cooling was observed during these two events. In addition, suspected volcano killers (Siberian traps and Emeishan volcano) also erupted after the main phase of extinction events. For example: the eruption of Siberian traps happened in 250 Ma, but the Permian-Triassic extinction happened in 251 Ma. Thus, volcano eruption is not likely the cause of massive extinction events.

Second, we will discuss about the famous KT impact theory. Several paleontologists (Professors Alvarez) proposed that an asteroid “Chicxulub” hit our earth about 65 Ma and killed all the dinosaurs . They suggested that Chicxulub hit Mexico gulf and they found evidences of Ir deposition in rocks during KT boundary. They suggested that large asteroid/comet hitting could produce dust and aerosols covering the sky and inhibit plant photosynthesis. Sulfur aerosol from sulfur-rich asteroid/comet could also cause global cooling. After calculation, all the dusts produced by asteroid or comet will drop down from atmosphere within several months. Based on Professor Brian Toon’s estimation, dust >4mg will drop down within 2 weeks and dust>2mg will drop down within 2 months. In addition, photosynthetic phytoplankton can form spore to become dormant during cold weather. Continental ferns can also produce spore during cold weather, and other conifers are highly resistant to cold weather. Some trees like Maples can drop their leaves and become dormant too. Thus, it is unlikely that plants are so vulnerable that they all died after several months. In addition, the sulfur aerosol can only cause mild and transient global cooling effect that is described in above paragraph. SO2 or NOx molecules will be washed out by rain within several months. Thus, it is also unlikely that asteroid/comet hitting could cause massive and long-term global cooling. In addition, recent evidences show that there was an interval of about 300 ka from the Chicxulub impact to the massive KT extinction event. Due to the lack of temporal association, the KT impact theory is unlikely the cause of KT extinction. In 2007, a new hypothesis suggested that the impactor of KT boundary was from Baptistina asteroid family not Chicxulub. However, it was recently discovered that 298 Baptistina doesn’t share the same chemical signature as the source of the KT impact . There is evident that dinosaurs died within 500 hundred years, but no strong evidences show that dinosaurs died within a short period of time. In addition, asteroid/comet theory cannot explain why only warm-blood mammals and birds survived after KT extinction. Thus, asteroid/comet impact theory is unlikely the cause of massive extinction events. 
 

Offline wanchung

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Evolution and extinction theory
« Reply #2 on: 07/02/2011 03:43:59 »
The third explanation is sea level change.     Sea level change has been associated with all Big Five massive extinction events, and this phenomenon is highly agreed by most scientists.  Sea level falls are found in the four massive extinction events. The lowest sea level was noted in the largest extinction event-End Permian extinction. Thus, sea level change is highly linked to massive extinction events. Researchers think that sea level fall can let animals and plants habiting in shallow sea to die. However, this theory cannot explain why continental plants and animals also died during these massive extinctions. There must be other reasons to explain the sea level change. In my opinion, sea level change is only a secondary event caused by global climate change. However, Dr. Hallam suggested a rapid sea level fall followed by sea level rise in the Triassic-Jurassic boundary.  If the rapid sea level fall was due to volcano cooling effect, the transient and mild 5-10 years global cooling induced by sulfur aerosol should not be observed geologically. Many researchers found that there was actually sea level rise without sea level fall in TJ boundary.    Global cooling can let sea level fall and global warming can let sea level rise. Thus, global climate change is the primary cause of massive extinctions.

Other explanations are less likely to be the primary causes of extinction events. Supernova gamma ray burst was suggested to be a cause of End-Ordovician extinction. Scientists estimated that supernova gamma ray burst happened for one time in the last 540 million years. They think the gamma ray burst(less than 6000 light year away) could sufficiently irradiate earth surface to kill organisms and destroy ozone layers. However, there is no evidence baking up there was such burst in the right time and right place. In addition, the geomagnetic field of earth could help to avoid the electromagnetic radiation and particles from outside universe like shielding solar wind. And, what is the relation between sea level change and gamma ray burst? Is gamma ray burst severe enough to cause massive extinction events? I severely doubt this. Another theory is plate tectonics or continental drift. Theorists think continental drift created a super-continent and reduced the area of continental shelf (the most species-rich part of the ocean). However, continental drift or plate tectonics is a very slow process. We can review the continental drift process. The Rodinia continent lasted from 1.1 billion years ago to 750 million years ago, and it was not associated with extinction. Pannotia continent formed between 600 million years ago to 540 million years ago, and it was not associated with extinction. Pangea existed from 500 Ma to 175 Ma. The first phase of Pangea splitting happened in 175 Ma and Laurasia and Gondwana were formed. The second phase of Pangea splitting happened in 140-150 Ma, and the Gondwana split into multiple continents including Africa, South America, India, Antarctica, and Australia. The third phase of Pangea splitting happened in 60-55 Ma, and Laurasia split into North America and Eurasia (current Europe and Asia Land). We can see none of the time sequences match the massive extinction events. How can it explain both the terrestrial and ocean organism extinctions? In addition, there is clathrate gun hypothesis. Methane clathrates form on continental shelves. These clathrates are likely to break up rapidly and release the methane if the temperature rises quickly or the pressure on them drops quickly (such as sea level fall situation). Methane is much powerful greenhouse gas than CO2. This clathrate gun hypothesis was proposed to explain the End-Permian extinction. It is because there was a decrease in the ratio of carbon-13 to carbon-12 (-0.009 ) during End-Permian period. However, many other events can reduce the percentage of carbon-13. Global cooling can let plants to release more CO2 which is composed of carbon-12. Plants can affect one-seventh CO2 concentration on earth each year. In addition, negative carbon excursion can be due to increased organism burial and decreased organism productivity during massive extinction. And, End-Permian period is related to global cooling not global warming. Thus, the clathrate gun hypothesis is unlikely.

Other interesting hypothesis may be the secondary events of climate change. First is the anoxic event hypothesis. Anoxic events are situations in which the middle and the upper layers of the ocean become lacking in oxygen. It is thought to be related to Ordovician-Silurian, late Devonian, Permian-Triassic, and Triassic-Jurassic extinctions, as well as a number of lesser extinctions. However, this anoxic event hypothesis can only explain the ocean organism extinctions not the terrestrial organism extinctions. And, if the photosynthetic phytoplankton were dead, they will reduce O2 production and release. Thus, the O2 level in ocean could decrease. Thus, anoxic event can be a secondary event after global cooling or global warming killing photosynthetic plants. The other interesting hypothesis is oceanic overturn. Oceanic overturn is a disruption of thermo-saline circulation which let surface water sink straight down, bringing anoxic deep water to the middle depths. Thus, it can kill most of the oxygen-breathing organisms which inhabit the surface and middle depths. Thus, it may help to explain the oceanic organism extinction. However, the oceanic overturn usually happens in the beginning or the end of glaciations. Thus, it is a secondary event of global cooling. The above two hypothesis can be secondary events after global climate changes
 

Offline wanchung

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« Reply #3 on: 07/02/2011 03:45:51 »
Finally, we will discuss about my hypothesis. Milankovitch hypothesis was proposed to explain the glaciations periods of earth. Due to the Milankovitch cycle, our earth will have climate periods from extremely warmness to extremely coldness.                 Since moderate climate are most suitable for bio-organisms, extremely warm or extremely cold periods will cause extinction events. Biological enzyme system works the best at core temperature 37。C, and higher or lower temperature can damage the activity of enzymes. The more temperature changes, the more enzyme activity loss will occur. Now the average environment temperature is around 25。C. Higher or lower temperature can hurt the survival of bio-organisms, especially during cold periods. Evidences show that the big five massive extinction events are all related to global climate changes. Global cooling is related to Ordovician-Silurian extinction (440-450 Ma), Late Devonian extinction (360-375 Ma), Permian-Triassic extinction (251 Ma), and Cretaceous-Tertiary extinction (70-65 Ma). Global warming is related to Triassic-Jurassic extinction (205 Ma), and it is associated with moderate Cenomanian-Turonian extinction (91.5 Ma). Sea level changes are all related to the Big Fives. Sea level rise was noted in Triassic-Jurassic extinction. And, sea level fall was associated with Ordovician-Silurian extinction, Late Devonian extinction, Permian-Triassic extinction, and Cretaceous-Tertiary extinction. We need to explain what mechanism induced sea level change. Global climate change is the best reason. Sustained global cooling can form more ice ridges or mountains, and then the content of ocean will be less. Sustained global warming can result in the melting of ice ridges or mountains, and the content of ocean will be increased. Thus, sea level change is just a secondary event of global climate change. The End Permian is the most severe extinction event, and the sea fell in the lowest level in End Permian period. We can deduct that the global climate change to cooling is most severe in End Permian period. Due to a research paper in Nature, earth temperature will rise 3。C before 2050, and 15%-37% organisms will be extinct. Due to the Copenhagen Diagnosis document, 40% organisms will die if temperature raises 5。C and 95% organisms will die if temperature raises 6。C. Thus, there is link between climate change and bio-organism survival.

We can look at the earth glaciations periods and their relations with extinctions. The Andean-Saharan ice age was from 450-420 Ma, and there is temporal association with the Ordovician-Silurian extinction (440-450 Ma). The Karoo ice age was from 360-260 Ma, and there is temporal association with the Late Devonian extinction (360-375 Ma). We can see extinction events occurred at the beginning phases of glaciations periods. There are no well documented ice age later, but we can look at the estimated climate graph by delta-O18 below. There was a sharp temperature drop in 260-250 Ma, and it could be associated with the End-Permian extinction (251 Ma). There was also a sharp temperature drop in 70 Ma which could be associated with Cretaceous-Tertiary extinction (70-65 Ma). This period is sometimes called Paleogene glaciations. How about the Triassic-Jurassic extinction 205-201 Ma? There is noted Milankovitch cycle related global warming during this period. Thus, Milankovitch cycle should be the reasons for all these extinction events.
 

Offline wanchung

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« Reply #4 on: 07/02/2011 03:46:41 »
We can examine the climate change patterns with these major extinction events in detail. There are well-documented evidences about the End Ordovician and Late Devonian glaciations. Global cooling was also reported in End Permian and End Cretaceous periods. In the Triassic-Jurassic boundary, global warming with increased fire activity was reported. In a paper, fossil plants are also found to have leave pattern (fossil leave width and stomatal density/size) implicating increased atmosphere CO2 suggested by the author.  However, increased heat in atmosphere itself can also lead leave width and stomatal density/size change.  Increased aromatic hydrocarbon concentration was also reported in T-J junction.  That could reflect the increased aromatic hydrocarbon substance after increased forest fire due to global warming. It is important to know the role of atmosphere CO2 in the extinction events. If volcano eruption is the reason of extinction events such as T-J green house period, then volcano released CO2 needs to play a dominant role. However, strong evidences showed that there is decoupling of atmospheric CO2 concentration and global climate change  . In addition, stabilized CO2 concentration was noted in TJ junction, so volcano eruption with CO2 release is unlikely the cause of extinctions.

We can also examine the extinction organism patterns to check our hypothesis. In End-Permian extinction event, the most vulnerable organisms are with low metabolic rate or weak respiratory system. If animals have high metabolic rate or strong respiratory system, they can be protected from cold climate due to more heat production. Thus, it is reasonable why animals with high metabolic rate survived after End-Permian extinction. It is reasonable that there was global cooling in End-Permian period. In addition, marine organisms with calcareous hard parts are vulnerable to extinct. This can be due to high ocean CO2 during this period. It is worth noting that plants prefer carbon-12 for photosynthesis and subsequent respiration. (CO2+H2O+sun-energy->O2+sugar; O2+sugar->CO2+H2O+bio-energy). When oceanic and continental plants died, they would decay and give off more CO2 with carbon-12. Thus, it can explain the decreased ratio of C-13/C-12 because of increased organism released CO2 with C-12. Decreased C-13/C-12 ratio can be also due to decreased plant productivity due to reduced C-12 intake by plants during massive extinction. That is why negative carbon excursion is frequently seen in extinction. If there is increased CO2 concentration in ocean, there is higher chance to have H2CO3 formation. When H2CO3 accumulates in ocean, the H+ will dissolve the CaCO3 shell of marine organisms. Thus, these marine organisms are highly vulnerable to this extinction event. The duration of End Permian extinction is 4-6 million years which can be explained by sustained global cooling. The long duration also suggests that a sudden event such as comet/asteroid impact or volcano eruption is not likely. A study said the Permian-Triassic junction is non-event which lets the impact or volcano theory unlikely. The duration of Late Devonian extinction is estimated to be 500000 to 15 million years. The long duration implies a sustained global event such as cooling. The most important groups to be affected by this extinction event were the reef-builders including the stromatoporoids, and the rugose and tabulate corals. These CaCO3 excreting organisms did not recover until the Mesozoic era. This phenomenon can be also explained by increased CO2 in ocean due to great animals/plants death. (CaCO3+CO2+H2O->Ca2+) In Ordovician-Silurian extinction event lasted for 10 million years, brachiopods, bivalves, echinoderms, bryozoans, and corals were most affected organism. There organisms all have calcareous exoskeleton and it can be also explained by above reason in Ordovician extinction. In K-T extinction, cold blood dinosaurs died and warm blood birds and mammals survived. Although some researchers suggested that dinosaurs could be warm blooded, recent findings show that most dinosaurs don’t have respiratory turbinates which are signature of warm blood animals. It suggested that K-T period is a global cooling period. On the other hand, majority of therapsids (ancestor of mammals) died in the Triassic-Jurassic boundary. Many therapids are found to have respiratory turbinates and are thought to be warm blood animals. Although warm blood animals have higher metabolic rate to generate more heat, they also have higher resting metabolic rate which costs a lot of energy. Thus, in warm period, warm blood animals don’t have survival advantages compared to cold blood animals such as dinosaurs. Thus, it is reasonable that Triassic-Jurassic boundary is a global warming period. In a moderate extinction period-Cenomanian-Turonian boundary event, many ancestors of whales and dolphins: ichthyosaurs were dead during this extinction event. Thus, it is reasonable that Cenomanian-Turonian junction is a global warming period.

In summary, we can see that global climate change is the actual cause of massive extinctions. Majority of extinction events are due to global cooling or global warming induced by Milankovitch cycle. The procession and axis tilt of earth can be affected by sun’s universal spinnity. However, sun’s spinnity is decreasing and decreasing due to transfer of angular momentum. Thus, the Milankovitch cycle should be prolonged. We can check these major extinction events due to global cooling. There was 80 Ma between End Ordovician extinction and Late Devonian extinction. There was 110 Ma between Late Devonian extinction and End Permian extinction. There was 180 Ma between End Permian extinction and End Cretaceous extinction. Thus, the duration of next possible major extinction is likely to be prolonged. There were at least 23 extinction events in earth history. If we want to use one single common reason to explain all the extinctions, Milankovitch cycle is the best choice. There are no strong evidences that multiple major comet impacts or many major volcano eruptions happened in these 23 extinction events. In addition, climate changes are associated with all the extinction events. But, the link of comet impact or volcano eruption to climate change is very weak. In addition, there were lacking temporal sequence between comet impact or volcano eruption and the extinction events. We can also use this theory to explain Cambrian explosion. During Cambrian period (530 Ma), all the major Phyla appeared with all diversity over a period of several million years. The evolution rate increased in an order of a magnitude. Darwin thought it is a puzzle. The Cryogenian ice age was from 800-630 million years ago. After the ice age, the earth temperature will become warmer gradually. During the Cambrian, the global climate of earth became most suitable for livings. Thus, Cambrian explosion occurred.  Darwin proposed that uniformitarianism is the usual mechanism for nature selection. However, catastrophism is also important in nature selection due to these major extinction events. In conclusion, we need to know the impact of climate change on earth to avoid the possible man-made extinction
 

Offline wanchung

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Evolution and extinction theory
« Reply #5 on: 07/02/2011 03:48:41 »
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Offline CliffordK

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Evolution and extinction theory
« Reply #6 on: 07/02/2011 10:07:56 »
Evolution and extinction

By Wan-Jiung Hu

The third explanation is sea level change.     Sea level change has been associated with all Big Five massive extinction events, and this phenomenon is highly agreed by most scientists.  Sea level falls are found in the four massive extinction events. The lowest sea level was noted in the largest extinction event-End Permian extinction. Thus, sea level change is highly linked to massive extinction events. Researchers think that sea level fall can let animals and plants habiting in shallow sea to die. However, this theory cannot explain why continental plants and animals also died during these massive extinctions. There must be other reasons to explain the sea level change. In my opinion, sea level change is only a secondary event caused by global climate change.
[...]
Global cooling can let plants to release more CO2 which is composed of carbon-12. Plants can affect one-seventh CO2 concentration on earth each year. In addition, negative carbon excursion can be due to increased organism burial and decreased organism productivity during massive extinction. And, End-Permian period is related to global cooling not global warming.
Is this your own research paper?
Somebody else's research paper?
Looking for comments?

I think we'll be learning a lot about climate change, forcing, and the ice ages in the next few decades.

"Recently" what has been happening is that when the temperature plunges.
The partial pressure of Carbon Dioxide (CO2) over the oceans drops.
This causes the oceans to absorb atmospheric carbon dioxide over a period of time (perhaps a few thousand years).
And, thus the levels of atmospheric carbon dioxide drop.

During the most recent few Glacial Periods, the levels of atmospheric CO2 have been hitting levels of about 180ppm which are very very low.

So, during a glacial period, several things hit the surface of the planet.
  • Cold Weather (ok, that is obvious)
  • Low CO2 on land
  • High CO2in the oceans (and potential acidification of the oceans)
  • Sea level drop, and potential exposure of continental shelves.
  • Potential increase in ocean salinity due to water loss.
  • Potential increase in acidity in the ocean due to absorption of CO2
There is apparently two types of Carbon Fixation.
C3: Does better than C4 with low CO2, low temperature levels.  Slightly lower 13C fixation with C3 plants.
C4: Does better with moderate temps, higher CO2 levels, slightly higher 13C fixation with C4 plants.

So...
Changes in 12C and 13C in either the atmosphere or in the biomatter would tell one which types of plants were most prevalent at the time. 

You didn't mention 14C which is essentially an indication of young carbon vs the other isotopes which would be older carbon.  So, for example, Methyl-Hydrate carbon, or carbon that has been locked in glaciers might be 14C deficient. 

Anyway, you will have to look at the timing, carbon sources, and etc to determine if there is a widespread shift from C3 to C4 plants or visa-versa.

If atmospheric CO2 dropped to 180ppm again, plants on the continents would not only grow poorly, but any animal life that depended on them would also grow poorly.  Plants and animals would be forced to migrate to "greener pastures". 

Marine plants would get lots of CO2.  But, the plants and animals would have to cope with the colder temperatures.  And, much of the marine life depends on the continental shelves.  If the continental shelves were to vanish, the marine animals would also suffer. 

It would all depend on the rapidity of changes.

In evolution...  What doesn't kill you makes you stronger.

If species evolved at a fairly stable environment.  They might have troubles to adapt to the fist climate change.

But, those that would survive would do better with future climate changes.

BTW:
A little better explanation of your goals would be nice.
Also, some pictures, graphs, whatever.
Something to break up the very heavy text.
 

Offline Bass

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Evolution and extinction theory
« Reply #7 on: 07/02/2011 17:05:22 »
wanchung

I'm curious as to why you believe all extinction events have to have a common cause?  Extinction events are obviously catastrophic (at least in geological time frames)- but there are multiple possible causes for catastrophic events.

Might suggest you also look at paleotectonics and position of continents during each event.
 

Offline CliffordK

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« Reply #8 on: 08/02/2011 00:49:50 »
There would likely be a few "causes".

Climatological
Asteroid (also related to climate).
Shifting continents could cause climate changes too.
Sea level changes.
Resource depletion.
New kid on the block.
Disease

Pretty much anything that could close a niche.
 

Offline Bob Dunn

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Evolution and extinction theory
« Reply #9 on: 09/02/2011 13:01:27 »
There would likely be a few "causes".

Climatological
Asteroid (also related to climate).
Shifting continents could cause climate changes too.
Sea level changes.
Resource depletion.
New kid on the block.
Disease

Pretty much anything that could close a niche.

and of course 'Self Destruction'
 

Offline CliffordK

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Evolution and extinction theory
« Reply #10 on: 09/02/2011 14:45:57 »
and of course 'Self Destruction'

True...
Is "Total Global Annihilation" a uniquely HUMAN concept?

All organisms must maintain a balance with "nature".  Those that can't maintain a balance are dealt with most harshly.

Also consider overpopulation and resource depletion. 
 

Offline tbarron

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Evolution and extinction theory
« Reply #11 on: 12/02/2011 17:40:06 »
"Recently" what has been happening is that when the temperature plunges.
The partial pressure of Carbon Dioxide (CO2) over the oceans drops.
This causes the oceans to absorb atmospheric carbon dioxide over a period of time (perhaps a few thousand years).
And, thus the levels of atmospheric carbon dioxide drop.

Is this what is meant by a "negative carbon excursion"?
 

Offline katesisco

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Evolution and extinction theory
« Reply #12 on: 16/05/2011 17:39:56 »
Lengthy discussion of climate which is not necessary; rather some attention to the fact the sun is demonstrating what D Bohm depicted as the Implicate Order.  We are indeed tied to all life.  Water is the holographic mirror. 
The 50 million year old extinction event is occurring as I type. 
 

The Naked Scientists Forum

Evolution and extinction theory
« Reply #12 on: 16/05/2011 17:39:56 »

 

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