Life on Earth Part 2

[Airbrush]

After the KT asteroid impact 65 million years ago, why did herbivours survive? If the asteroid threw molten rock high into the atmosphere, which rained down all over the Earth, that would have burned up all vegetation on the planet. That global-wide fire would have been followed by an "Asteroid Winter" and no plants would grow for months or years. What did the surviving mammal herbivours eat during this time? Herbivours should not have survived, and yet they did.

[pwagen]

Why would it have "burned up all vegetation"? There was no global-wide fire.

 

The skies were covered with ash and the like, and plants had problems growing. That doesn't mean every single plant died or couldn't grow.

 

The event wasn't black and white to the point that "x died and y lived". Lots of animals died, both carnivores and herbivors, as well as lots of plants. But a lot of everything managed to survive, including plants.

[Airbrush]

"Why would it have "burned up all vegetation"? There was no global-wide fire."

 

According to current theory the KT asteroid burned up all vegetation on Earth from global-wide molten rain of rocks. This was immediately followed by asteroid winter. How did herbivours survive?

[Moontanman]

"Why would it have "burned up all vegetation"? There was no global-wide fire."

 

According to current theory the KT asteroid burned up all vegetation on Earth from global-wide molten rain of rocks. This was immediately followed by asteroid winter. How did herbivours survive?

 

 

 

I'm not completely sure of what you are saying here. Are you saying that herbivores couldn't have evolved after the K/T extinction? At the time of the K/T extinction most if not all mammals were insectivores, various herbivores and carnivores evolved well after the K/T extinction.

[pwagen]

According to current theory the KT asteroid burned up all vegetation on Earth from global-wide molten rain of rocks.

I'll have to ask for your source on this. While a lot of plants (and animals) died and went extinct, not "all vegetation" was burned to a crisp. If, indeed, all plants were burned, wouldn't it also be likely that animals everywhere were scorched to death as well? Why would the molten rain effect only plants?

 

 

There is overwhelming evidence of global disruption of plant communities at the K–T boundary.^{[12][12][52][53]} Extinctions are seen both in studies of fossil pollen, and fossil leaves.^[12] In North America, the data suggest massive devastation and mass extinction of plants at the K–T boundary sections, although there were substantial megafloral changes before the boundary.^[12][54] In North America, approximately 57% of plant species became extinct. In high southern hemisphere latitudes, such as New Zealand and Antarctica the mass die-off of flora caused no significant turnover in species, but dramatic and short-term changes in the relative abundance of plant groups.^[50][55]

http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event#Terrestrial_plants

[Arch2008]

Perhaps this should be asked in the Biology section? Other than the asteroid impact part, I don't see how this is astronomy or cosmology.

[Airbrush]

OK, I'm going to ask this question in the biology section.

 

pwagen: "I'll have to ask for your source on this. While a lot of plants (and animals) died and went extinct, not "all vegetation" was burned to a crisp. If, indeed, all plants were burned, wouldn't it also be likely that animals everywhere were scorched to death as well? Why would the molten rain effect only plants?"

 

My sources are several recent science programs I've seen on Science Channel. All vegetation did not go extinct, but it was all gone long enough (months at least) for herbivours to all become extinct. All I can think of is the only surviving animals were either carnivours or omnivours, later herbivours evolved from the surviving omnivours.

 

I'm signing out here, next post to Biology.

This is as close as I can find on Wiki:

"....Omnivores, insectivores and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. At the end of the Cretaceous there seems to have been no purely herbivorous or carnivorous mammals. Mammals and birds that survived the extinction fed on insects, worms, and snails, which in turn fed on dead plant and animal matter. Scientists hypothesize that these organisms survived the collapse of plant-based food chains because they fed on detritus (non-living organic material)."

http://en.wikipedia.org/wiki/KT_extinction

[pwagen]

My sources are several recent science programs I've seen on Science Channel. All vegetation did not go extinct, but it was all gone long enough (months at least) for herbivours to all become extinct.

Science programs tend to exaggerate a lot of things. After all, they're made partly for entertainment. The notion that it was "all gone" doesn't hold water. If it was all gone, why do we have plants now (sorry for sounding like a creationist)? I dare say 65 million years is a short span when it comes to evolving new plants from scratch, so there must have been something left. Another sign of this is plants such as fern, that were around from before the event, surviving until present.

 

It might very well be like Moontanman said above, that most mammals were insectivores. This would also allow plants to grow back, since they had nothing that would use them as food until later. But suggesting herbivores didn't survive because there were no plants, I personally have a hard time seeing that.

[Phi for All]

OK, I'm going to ask this question in the biology section.

!

Moderator Note

So you can have all responses in the same thread, I moved this one to Biology.

[Airbrush]

Hi pwagen, in case you haven't notice this, here it is from wikipedia"

 

"...Mammals and birds that survived the extinction fed on insects, worms, and snails, which in turn fed on dead plant and animal matter. Scientists hypothesize that these organisms survived the collapse of plant-based food chains because they fed on detritus (non-living organic material)."

 

The science programs had reputable scientists stating these things. My commentary is flawed. All vegetation would have burned off in global-wide fires. Some plants did not go extinct, but they were gone for months or years. Animals fed on insects and creepy crawlies, which fed on dead plant & animal material. And after a while, many species of plant life returned from "hibernation" when there was enough sunlight.

Edited April 2, 2013 by Airbrush

[pwagen]

I seem to stand corrected on the plants being dead. I still don't agree that it was the flames that killed them, I would imagine the ash clouds could have, but dead they seem to have been.

 

However, I would still like to know what the plants sprung up again from if they were all dead. Seeds buried in the ground that only emerged once the ash clouds had dissipated? Will look into this more at some later time.

[Ophiolite]

I have not examined the literature on this for at least a decade. The initial idea was that there was a global 'fire flood' from impact ejecta re-entering the atsmosphere around the planet. A worldwide ash horizon was cited as evidence of this. Further research tended to the view that the total destruction of living plant life was not global in extent. The burst of fern growth shortly after certainly points to a devastaing impact on the other plant life. This was a question that was being actively debated in the 90s. I'll see what i can find about current views.

 

This 2009 paper is an illuminating review. Here is a telling extract:

 

It is recognized that there was a major disruption to plant communities across the K-Pg boundary (Tshudy et al., 1984; Sweet, 2001; Nichols and Johnson, 2002). These new modelbased results, taken together with the abundant literature on paleontological indicators of fire occurrence, suggest that extensive wild fires were not the cause.

 

 

You may also find Plants and the KT Boundary of interest. I have not yet had an opportunity to digest it.

Edited April 3, 2013 by Ophiolite

[Ophiolite]

The battle continues: Robertson, D.S. et al "K-Pg extinction: Reevaluation of the heat-fire hypothesis" Journal of Geophysical Research: Biogeosciences March 2013

 

Abstract

The global debris layer created by the end-Cretaceous impact at Chicxulub contained enough soot to indicate that the entire terrestrial biosphere had burned. Preliminary modeling showed that the reentry of ejecta would have caused a global infrared (IR) pulse sufficient to ignite global fires within a few hours of the Chicxulub impact. This heat pulse and subsequent fires explain the terrestrial survival patterns in the earliest Paleocene, because all the surviving species were plausibly able to take shelter from heat and fire underground or in water. However, new models of the global IR heat pulse as well as the absence of charcoal and the presence of noncharred organic matter have been said to be inconsistent with the idea of global fires that could have caused the extinctions. It was suggested that the soot in the debris layer originated from the impact site itself because the morphology of the soot, the chain length of polycyclic aromatic hydrocarbons, and the presence of carbon cenospheres were said to be inconsistent with burning the terrestrial biosphere. These assertions either are incorrect or have alternate explanations that are consistent with global firestorms. We show that the apparent charcoal depletion in the Cretaceous-Paleogene layer has been misinterpreted due to the failure to correct properly for sediment deposition rates. We also show that the mass of soot potentially released from the impact site is far too low to supply the observed soot. However, global firestorms are consistent with both data and physical modeling.

 

 

I don't think the disagreement on this point is going to go away anytime soon. Which is good, as it makes for interesting science.

[Airbrush]

Thanks Ophiolite for the good info on an interesting topic!