What caused marine dinosaur extinction?

[The Peon]

I tried doing some google searches and read a few articles as well as doing a search here, but I have not found any info on why marine dinosaurs went extinct. It seems rather odd if it was a meteor impact that it would cause extinction of some fish and not others. Is there any explanation as to why bony fish, sharks and a few other marine animals made it through but marine dinosaurs and other types of marine monsters that existed back then did not?

[Moontanman]

There were no marine dinosaurs Peon, but the marine reptiles often characterized as dinosaurs became extinct at the end of the Cretaceous (the ones that made it that at least to the Cretaceous) died off due to the collapse of the marine food chain, the K/T extinction had a profound influence in the sea as well as on land and many marine species both microscopic and macroscopic became extinct as well. Sea turtles are thought by some to be the sole remaining members of the marine reptile groups.

[Marat]

What about the live coelacanth, of a species thought to have been extinct since the late Cretacean Period, which was caught off the coast of South Africa in 1938?

[Moontanman]

What about the live coelacanth, of a species thought to have been extinct since the late Cretacean Period, which was caught off the coast of South Africa in 1938?

 

 

I'm sorry Marat, but what does the Coelacanth have to do with the extinction event that caused the deaths of the marine reptiles? No one says everything died at the KT boundary, some animals did survive, I gave an example, sea turtles, there are many more that did survive but not any of the marine reptiles other than the sea turtle.

[The Peon]

There were no marine dinosaurs Peon, but the marine reptiles often characterized as dinosaurs became extinct at the end of the Cretaceous (the ones that made it that at least to the Cretaceous) died off due to the collapse of the marine food chain, the K/T extinction had a profound influence in the sea as well as on land and many marine species both microscopic and macroscopic became extinct as well. Sea turtles are thought by some to be the sole remaining members of the marine reptile groups.

 

 

What exactly are the specifics of this collapse? If most land animals died off, how would that affect the seas? Can you give a few scenarios and explanations? I read a lot about the K/T extinction event but all the sources I read touch only on land animals.

[Chalky]

What exactly are the specifics of this collapse? If most land animals died off, how would that affect the seas? Can you give a few scenarios and explanations? I read a lot about the K/T extinction event but all the sources I read touch only on land animals.

 

Well, there's a lot of debate about how the extinction happened in the first place. But the ocean is quite a sensitive system.

 

If we look at the oceans today, rising atmospheric CO2 is making them more acidic. Every time El Nino happens in the Pacific, the current flow reverses direction and causes marine life to die off South America.

 

Add in a massive catastrophic event like a meteorite or a big volcanic eruption and the effects on the oceans could be massive.

[Moontanman]

What exactly are the specifics of this collapse? If most land animals died off, how would that affect the seas? Can you give a few scenarios and explanations? I read a lot about the K/T extinction event but all the sources I read touch only on land animals.

 

 

The main thing to remember is that the disaster that wiped out the dinosaurs severely affected the entire planet.

 

http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Tertiary_extinction_event

[Athena]

The Peon's question and Chalky's answer motivated me to google CO2 and acidic oceans and I got this

 

http://www.realclimate.org/index.php/archives/2005/07/the-acid-ocean-the-other-problem-with-cosub2sub-emission/

 

According to this site, our seas could be in serious trouble, because burning fossils fuels is releasing CO2 which is interacting with the seas, too fast. The mechanism that gets the ph at a desired level can not keep up with the rapid pace of CO2 making the seas too acid.

 

So if the event that caused the dinosaurs to go extinct, involved sudden high levels of CO2, the seas would have become too acid too fast, and marine creatures could not adjust fast enough? However, 800,000 years ago the oceans were more acid than they are today. It is my understanding the problem would be the speed of the change. If things change slowly everything has time to adjust. If there is a sudden change, things don't have time to adjust.

[Marat]

And what made the oceanic dinosaurs so much more sensitive to the sudden and massive environmental change than the other oceanic creatures which did survive this boundary?

[Ophiolite]

And what made the oceanic dinosaurs so much more sensitive to the sudden and massive environmental change than the other oceanic creatures which did survive this boundary?

You are assuming they were more sensitive. The reverse could still have been true and they would still have died out. How many herring are there on the planet? Many millions. Wipe out the vast majority of them and you still have a viable breeding number available to repopulate the oceans. You don't, however, have enough to feed the appetites of large marine reptiles. Ergo, out they go.

[The Peon]

I read that wikipedia article and a few others, but it still does not make full sense to me. Is this correct to assume: The change in atmosphere was sudden and drastic, affecting the plant life and smallest of creatures in the oceans food chain. This in turn caused larger fish and animals to "thin out" and many died off, some species even became extinct. Then since the smaller "game" fish were so few in numbers, the larger predators died off from starvation?

Edited May 17, 2011 by The Peon

[Moontanman]

I read that wikipedia article and a few others, but it still does not make full sense to me. Is this correct to assume: The change in atmosphere was sudden and drastic, affecting the plant life and smallest of creatures in the oceans food chain. This in turn caused larger fish and animals to "thin out" and many died off, some species even became extinct. Then since the smaller "game" fish were so few in numbers, the larger predators died off from starvation?

 

 

The "change" in the atmosphere was that suddenly the light from the sun was cut off by ash, dust and smoke, an asteroid strike on one side of the earth and a huge lava flow almost on the other side pretty much kicked up enough material to cut off sunlight for possibly years, months at least, it's quite possible the flood of basalt lava had been going on for thousands of years, the asteroid strike could have just been the straw that broke the camels back, this destroyed the bottom of the food change, most all the tiny animals who used sunlight died, then the ones who ate them died and so on. The tiny producers didn't die out completely but not enough survived to support the food chain and the bigger animals tended to die off. There were exceptions but most of the larger sea creatures died off much the same way the larger land creatures died off as well.

[Athena]

And what made the oceanic dinosaurs so much more sensitive to the sudden and massive environmental change than the other oceanic creatures which did survive this boundary?

 

The link explains the ph level is different near the surface than it is near the bottom. So depending on which area of the ocean something lives, it has a better or worse chance of surviving. I assume the creatures that survived had a better place. Then when the big guys were gone, they could spread and multiple. When the dinosaurs died the mammals took their place, right? So as ocean conditions change, some loose the advantage and others gain.

 

The "change" in the atmosphere was that suddenly the light from the sun was cut off by ash, dust and smoke, an asteroid strike on one side of the earth and a huge lava flow almost on the other side pretty much kicked up enough material to cut off sunlight for possibly years, months at least, it's quite possible the flood of basalt lava had been going on for thousands of years, the asteroid strike could have just been the straw that broke the camels back, this destroyed the bottom of the food change, most all the tiny animals who used sunlight died, then the ones who ate them died and so on. The tiny producers didn't die out completely but not enough survived to support the food chain and the bigger animals tended to die off. There were exceptions but most of the larger sea creatures died off much the same way the larger land creatures died off as well.

 

 

Moontanman, given your experience with aquariums, I expect you to say more about PH levels.

 

This is from the link I posted.

 

 

 

Elevated CO₂ levels also affect fish and other aquatic organisms, in part because of the decrease in pH, but also because CO₂ is what heterotrophic organisms try to exhale. However, we should note that dissolved CO₂ levels were substantially higher than today in the geologic past, and organisms were able to cope with this OK, so apparently there can be some acclimation of populations to higher CO₂.

 

The natural pH of the ocean is determined by a need to balance the deposition and burial of CaCO₃ on the sea floor against the influx of Ca²⁺ and CO₃^2- into the ocean from dissolving rocks on land, called weathering. These processes stabilize the pH of the ocean, by a mechanism called CaCO₃ compensation. CaCO₃ compensation works on time scales of thousands of years or so. Because of CaCO₃ compensation, the oceans were probably at close to their present pH of around 8 even millions of years ago when atmospheric CO₂ was 10 times the present value or whatever it was. The CaCO₃ cycle was discussed briefly in regards to the uptake of fossil fuel by the ocean, here. The point of bringing it up again is to note that if the CO₂ concentration of the atmosphere changes more slowly than this, as it always has throughout the Vostok record, the pH of the ocean will be relatively unaffected because CaCO₃ compensation can keep up. The fossil fuel acidification is much faster than natural changes, and so the acid spike will be more intense than the earth has seen in at least 800,000 years.

 

 

 

The spike of CO2 in the air, caused by the asteroid and volcano, mixes with the water, and changes the PH too fast for the creatures to adjust, so they die. I believe want lives closest to the surface is in the most danger and whatever feeds on what lives close to the surface.

 

This explanation, of what acid rain does to water creatures, may help

 

http://www.epa.gov/a...face_water.html

 

Acid rain causes a cascade of effects that harm or kill individual fish, reduce fish population numbers, completely eliminate fish species from a waterbody, and decrease biodiversity. As acid rain flows through soils in a watershed, aluminum is released from soils into the lakes and streams located in that watershed. So, as pH in a lake or stream decreases, aluminum levels increase. Both low pH and increased aluminum levels are directly toxic to fish. In addition, low pH and increased aluminum levels cause chronic stress that may not kill individual fish, but leads to lower body weight and smaller size and makes fish less able to compete for food and habitat.

 

Some types of plants and animals are able to tolerate acidic waters. Others, however, are acid-sensitive and will be lost as the pH declines. Generally, the young of most species are more sensitive to environmental conditions than adults. At pH 5, most fish eggs cannot hatch. At lower pH levels, some adult fish die. Some acid lakes have no fish. The chart below shows that not all fish, shellfish, or the insects that they eat can tolerate the same amount of acid; for example, frogs can tolerate water that is more acidic (i.e., has a lower pH) than trout.

Edited May 17, 2011 by Athena

[Moontanman]

The link explains the ph level is different near the surface than it is near the bottom. So depending on which area of the ocean something lives, it has a better or worse chance of surviving. I assume the creatures that survived had a better place. Then when the big guys were gone, they could spread and multiple. When the dinosaurs died the mammals took their place, right? So as ocean conditions change, some loose the advantage and others gain.

 

 

 

 

Moontanman, given your experience with aquariums, I expect you to say more about PH levels.

 

It is indeed my experience with pH and the effects it has on aquatic life that shows me that pH was no doubt part of the problem but not a very large part of it. There are habitats, large important habatats i might add, that shift their pH from 8 to 6 or so twice daily and they are rich with life forms comparable to coral reefs. Fish and most marine organisms are quite tolerant of pH changes. Even marine coral which i have considerable experience with do not just die when the pH changes and unless the ("quick", indeed the speed needs to be defined as well) change is more than 2 pH numbers or involves crossing pH 7 in one direction of another I see no way for pH to be a large part of the mechanism that resulted in the extinction of much of the life on the Earth at the K/T boundary.

 

The spike of CO2 in the air, caused by the asteroid and volcano, mixes with the water, and changes the PH too fast for the creatures to adjust, so they die. I believe want lives closest to the surface is in the most danger and whatever feeds on what lives close to the surface.

 

 

I still think that lack of sunlight for months or even years was the deciding factor, life can and does adjust to changes in pH, no light is far more of a problem.

 

 

This explanation, of what acid rain does to water creatures, may help

 

Considering I see nothing to indicate we are talking about the oceans pH of 8.3 or so changing to pH 5, I'm not even sure this would be possible over the times scales of the K/T extinction such a change would be evident in the chemistry of sediments and we do not see such a change. A change in pH of 1 is a ten X change, dropping the pH from 8 to 5 of the entire oceans or even to below 7 is highly improbable especially when you take into account that pH of the oceans was still 8 or more when the atmosphere contained far more CO2 than it does today, the ocean has a tremendous amount of buffering capacity and the larger an organism is the less it is affected by pH changes, the acid rain changes you are speaking of occur in very limited habitats and only affect certain fishes and the pH change is quite large from above neutral to 5, pH 5 will burn your skin if you have a scratch or other wise broken skin but there are many fish that not only live at this pH but have to have it to breed and hatch their eggs.

 

lack of sunlight is the deciding factor, pH changes would have been the least of the worries of animal life with no sunlight.

Edited May 17, 2011 by Moontanman

[The Peon]

Thanks guys you made it pretty clear and understandable.