K-Pg: the demise of non-avian dinosaurs and rise of mammals
Survival of the Chicxulub asteroid
Impact and Mass extinctions
Survival in the first hours of the Cenozoic
By: Douglas S. Robertson et al. 2004
This paper covers survival of the initial devastating
effects of the Chicxulub impact on animals, birds, insects and plants. Their
main argument is that sheltering behaviors developed long before the Cenozoic,
either underground, in cavities of rocks or vegetation, or under water were
significant factors in survival of the initial high temperatures; fires; high
levels of dust, soot and acid rain; infra-red thermal radiation; and falling
spherules from the bolide impact. They state that it is clearly not the only
factor to survival, but it is a major one. In their study, they looked at some
of the hypothesized global stresses and summarize how these factors could be
survived. The most effective method of survival is sheltering or aestivation,
especially for the first few minutes to hours, to possibly months. Atmospheric
affects would have come from the entire sky, not just from above, but from all
sides. The effects of this bolide impact were felt globally, as is evidenced in
soot from the wildfires started by the reentering ejecta that is found in the
K-T boundary rock layers. They suggest that the kill-mechanism of terrestrial
organisms was the thermal pulse which ignited the fires, causing the
incineration of all organic biomass above-ground, which left the amount of soot
present in the rock and soil levels of this boundary period. Non-sheltering
habits of organisms favored smaller animals which could easily shelter,
resulting in animals of larger body sizes and with habits of being out in the
open did not survive the initial impact effects. After the initial impact,
survivors needed to survive predation, the finding of food, and the finding of
suitable habitats. In the longer term, the survivors needed to deal with
population explosions as larger predators had vanished and the evolutionary
opportunities to fill niches that had been vacated. Many survivors were not
successful in surviving all these stresses. They focus on mammals and birds,
indicating that most mammals that survived had body masses of between 10 – 100
kg and that most birds that survived were most likely shore or water birds.
Most fossils of birds that have been found were located in the preferred
shorebird habitats, but this could be misleading as old bird bones are fragile
and rarely survive to become fossils. Many lineages seem to disappear, becoming
“ghost” lineages, only to reappear later, having yet to appear as fossils.
Terrestrial plants seemed to have survived by having strong, underground
vegetative parts which could regrow, or had a bank of seeds already in the soil
ready to regenerate when the environment became favorable. Rapid radiation of
species was directly related to the vacant niche filling opportunities that
allowed the dispersal of the small sheltered populations.
Questions:
1)
Why was it so important for
terrestrial organisms to find shelter during the first few hours following the
Chicxulub bolide impact?
2)
How would a double-impact have
affected the outcome of the Chicxulub impact?
3)
How was the IR flux responsible
for being the kill-mechanism of non-marine, terrestrial organisms in the first
few hours after the Chicxulub impact?
4)
What were some of the survival
strategies of the surviving terrestrial and avian groups?
5)
Why was living in water a
successful strategy for survival immediately after the Chicxulub impact?
The
Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene
Boundary
Schulze et al. 2010
In this
paper, the authors discuss how abrupt biota changes during the
cretaceous-paleogene periods are due to the hypothesis that an asteroid hit the
earth causing major changes in the environment. Evidence for this asteroid
impact comes from impact ejecta, Ni-rich spinels and shocked minerals along the K-Pg boundary. The
ejecta distribution leads researchers to believe that the impact is found along
the Gulf of Mexico Caribbean region. Along with the evidence of the
ejecta distribution, there was also a discovery of the 200km in diameter
Chicxulub crater structure along the Yucatan peninsula in Mexico. In
turn, modeling suggests that the size of the crater and the release of
climatically sensitive gasses from the carbonate and sulfate rich target rocks
caused very drastic environmental effects such as darkness, global cooling, and
acid rain. K-Pg boundary sites show distinct ejecta distribution patterns
relating to distance from the Chicxulub crater. The patterns are broken
up into four parts, which include very
proximal, proximal, intermediate and distal
distances more than 5000km from Chicxulub.
The
author shares four alternative hypotheses that oppose the current asteroid
impact causing the K-Pg mass extinction. The first suggests that the clastic
unit is a long term depositional sequence genetically unrelated to the
Chicxulub. The second suggests that Chicxulub impact preceded the K-Pg
boundary and predicts
that Deccan flood basalt eruptions was responsible for the mass extinction. The third
hypothesis suggests that 3mm thick clay layer in the Brazos river site
originated from the Chicxulub impact, suggesting that the impact occurred
significantly before the K-Pg boundary. The fourth hypothesis suggests that a
50cm thick sandstone unit between impact breccias and lower Paleocene post impact crater
infills contain Cretaceous planktic foraminifera, suggesting that the impact
preceded the K-Pg mass extinction. All four of these hypotheses were
rejected by the author for various reasons.
Consequences
of the impact from Chicxulub were large enough to generate earthquakes, shelf
collapse of the Yucatan platform and widespread tsunamis across the coastal
zones of surrounding oceans. The impact models suggest the impact had
sufficient energy to distribute materials around the world. Near-surface
target material was ejected ballistically at high velocities, which yielded a
thick spherule layer at proximal sites and a basal layer at intermediate
distances. Projectile plume deposits associated with this impact generated the
formation of the upper layer in intermediate distances and contributed to the
clay layer in distal distances.
Reentry
of the ejecta spherules caused a global pulse of increased thermal radiation
resulting in thermal damage to the biosphere. In
the models, carbonates of the ejecta and soot have been projected to produce
large amounts of dust in the atmosphere. Terrestrial land was also greatly affected by sulfur
released from the meteor. The sulfur was transformed to sunlight absorbing
sulfur aerosols causing a cooling of the earth by 10 degrees Celsius for ten
years. The sulfur generated acid rain, which greatly affected terrestrial lands
and surface marine waters. A combination of all three of these factors
would have magnified environmental consequences compared with more prolonged
volcanic effects.
As a
result, a number of major animal groups disappeared and only a few of these
major groups did not suffer complete loss of species. Marine photoplankton,
major drivers of ocean productivity, were affected tremendously due to the
darkness. There was also a major difference in survivorship between
photoplankton with calcareous shells and siliceous shells. Extinction of
calcareous primary producers caused major starvation to other organisms higher
in the food chain. Numerous effects on land included loss of diverse
vegetation, destruction of diverse forest communities and a shut down of
photosynthesis.
Questions:
1. Would you find any of the four
alternative hypotheses to have contributed to the
K-Pg mass extinction? Why or why not?
2. Which proximal cause from the impact
do you think affected organisms on land or sea the most and why?
3. This paper downplays the event of
widespread wild fires for the Chicxulub impact and suggests that they would
only be localized to where the impact occurred. In the paper by Robertson
et al, he suggests that there was widespread global wildfires. Do you
think the impact caused global wildfires? Why or why not?
Decoupled
Plant and Insect Diversity After the End-Cretaceous Extinction
By:
Wilf Et Al. (2006)
Following the K-T (K-Pg) mass extinction,
a recovery period typically lasting around 3-4 million years occurred to re-diversify
life. However, there is a gap in the fossil record that makes the rebuilding of
food webs difficult. A popular theory of biodiversity rebuilding is that
primary producers first appear and then successive consumers follow. This theory aligns with modern ecological
observations of insect herbivore diversity and plant diversity being
correlated. Wilf et al. studied how the presence of insect damage on
fossilized leaves could provide insight into food web recovery at Cretaceous,
Paleocene, and Eocene sites. The study looked at insect mines within leaves-
which is a type impression left from insect larva living and feeding on the
foliage. The study evaluated a total of 15,000 angiosperm leaves for the presence
of 63 distinct insect damage patterns. All of the sites were located in the
western interior United States, in North Dakota, Wyoming, and Colorado. The sites were that of warm and subtropical
influence controlled for similar sample sizes, diversity, preservation, and stratigraphic
influences. It was found that the insect
diversity and plant diversity dropped simultaneously and remained low until the
start of the late Paleocene. The Paleocene
sites can be characterized by low overall floral diversity with the exception
of the Castle Rock site. The Castle Rock site was very diverse but only had two
types of mines (hosts and morphologies). The Cretaceous sites are known for having rich
floral diversity. A site named Mexican Hat was similar to the diverse
Cretaceous flora environments and again unlike most Paleocene locations. Here
the mining frequency was double the amount of other Paleocene sites. Mexican Hat mine morphologies are unique in
that they are rare within other fossil record- suggesting that this area had
regionally evolved taxa not correlated with K-T survivor species. It seems as
though the insect and plant food web recovery began during the late Paleocene
and that herbivory led the plant diversity. Paleocene flora have few mines
compared to the Cretaceous. It is believed that the Castle Rock location was
mostly composed of thin-leaved deciduous hosts that were unable to defend
against the colonization of herbivores, this was also seen at Mexican Hat.
What can be concluded from the unique
food web systems at Castle Rock and Mexican Hat is that there was a greater
amount of variance of food web interactions in localized regions which suggests
an imbalance. The conclusions of this study found that there was an imbalance
of food webs based off of insect mining on angiosperm leaf fossils for 1-2
million years after the K-T mass extinction.
1) What else do you think might be valuable information
towards reconstructing a food web after a mass extinction? Are there any modern
or more contemporary examples you can think of?
2) How do you think atypical localized regions of diversity
occur?
3) Does it surprise you that this study found that food web
recovery can be unstable?
Robertson et. al. Paper
ReplyDeleteIt was important to seek shelter following the impact, so as to try and avoid the world wide sweep of IR radiation that resulted from it, and those who couldn’t were sadly those who also went extinct. A double impact wouldn’t really have affected the Chicxulub impact, as it was so massive that other possible double impacts were either very locally bad or negligible at best to the main impact. The IR blast was the kill mechanism, because it was not the proximal cause which would be mass cancer and radiation poisoning, but was also not the ultimate cause which was the meteorite impact. Living in the water was also a viable survival strategy for the next few hours after the impact, because the water that you lived in acted as a buffer between you and the IR blast.
Schulze et al. Paper
I believe that the four alternative hypothesis put forward by the authors of this paper would not have contributed to the K-Pg extinction by themselves, however I do believe that the volcanism mentioned would have contributed to the mass extinction after the impact as the impact probably would have triggered a lot of volcanic activity that would in turn spew even more greenhouse gases into the air. I think the radiation sickness released from all the stirred up heavy metals and IR blast was the worst proximal cause as it went worldwide and can/did hit anything that could not quickly find cover underground or lived in the water already. I believe that it likely only because local wildfires except for triggered volcanism events.
Wilf et al. Paper
I think knowing what kind of organism that survived a mass extinction compared to who died during it is very important in discovering how a food web rebounds from the same mass extinction. This will tell us what niches are empty and which animals are more likely to fill those niches, also it will reveal which food sources are still available if not many herbivores are left that means carnivores are likely to decline for a while etc. I’m not surprised that the study found that food web recovery can be unstable, because it depends on so many factors that are hard to determine exactly and that can be interpreted in multiple ways so it will always be hard to get a clear picture of a food web rebound and it is even shakier when you are one of those organisms whose whole world and food supplies have changed in an instant.
Robertson et. al.
ReplyDeleteIt was so important for terrestrial organisms to find shelter during the first few hours following the impact to avoid the wide spread IR radiation and other more regional effects of the impact like forest fires and tsunamis. A double impact I don’t think would have had much of an additional affect due to such a significant impact created by the initial impact. Some of the survival strategies of the surviving terrestrial groups were to burrow and find shelter underground so that they could escape the IR radiation and heat pulse. Living in water was also a successful strategy because like burrowing being under water would allow organisms to escape the heat flux caused by the initial impact.
Schultze et. al.
I don’t think that any of the four alternative hypotheses contributed to the K-Pg however I do think that volcanism was affected by the initial impact of the meteorite like one of the hypotheses talks about. However, I believe that the hypothesis was wrong to state that the impact was prior to the mass extinction because of all the data that points to the meteorite coinciding with the date of the beginning of the K-Pg. I think that the radiation and heat flux was the proximal cause that affected organisms on land and sea the most because of how intense it was and there was really no way to avoid it except hiding underground or under water. I believe that the impact would have caused global fires because the ejecta from the impact would have heated up a lot as it reentered the Earth's atmosphere and then the IR radiation from the upper atmosphere would have ignited fires around the globe.
Wilf et. al.
I think that knowing the species that went extinct would be valuable towards reconstructing a food web because it would give you information about which species are no longer in a certain niche and so what other food source an animal that survived would need to go to if their previous food source was gone. However, it does not surprise me that this study found that food web recovery was unstable because of the difficulty of putting a food web together before a mass extinction. Having to do one after a mass extinction when complete niches are gone or when a specific organism is the only one to survive after a mass extinction would be difficult to put into a food web. I also think there are a lot of various aspects that go into creating a food web that is made even more difficult after a mass extinction.
The meteor impact near the Yucatán peninsula was clearly an ultimate cause of the end-Cretaceous mass extinction. The hypothesis that heat, generated from the re-entry of ejecta from the initial impact, was sufficient to kill off surface dwelling terrestrial life is reasonable. With as much as 500 million joules per square meter of infrared radiation, any biological organism left exposed would die rather quickly. However, there had to have been other kill mechanisms. Robertson et al. illustrate this when they discuss specific habitats. “Living in a lake, stream, or marsh would have been advantageous”. Semiaquatic animals may even have been spared, taking refuge in marshes or swamps that provide some foliage. Crocodiles and turtles survived. Plesiosaurs and mosasaurs all went extinct. If no fossils of these animals can be found above the K-Pg boundary, and we accept the meteor as the ultimate cause, then other processes of equal rapidity must have been occurring.
ReplyDeleteRobertson:
ReplyDeleteTerrestrial organisms were left exposed to the effects of the meteorite, which were local and widespread. Local and immediate effects organism were exposed to were the impact blast and heat pulse, as well as fires, soot, lead and metal in soils, and disruption of photosynthetic organisms in area. This would have led to deadly temperatures (incineration), burns, cooling, poisoning, and perhaps a lack of vegetation for food. If the organisms were sheltered, they could have avoided these effects. Living in water essentially acted as a survival strategy because they would not have been effected by the heat blasts (could go to deeper or cooler water), did not have to worry about fires, and although the debris could cause acid rain, it was not an immediate effect.
Schultze:
I think that the wildfires were relatively widespread, given the evidence presented by Robertson. Although the thermal blast was short lived, it caused spherules to disperse across the globe , and upon reentry they could have caused fires in dry forests. The end cretaceous was warm, therefore there could have been a large amount of dry vegetation to catch fire from the radiating spherules. Although the spherules haven’t been well sampled outside of N. America and Europe, they have been found in diverse localities, such as New Zealand and the South Atlantic.
Wilf:
It does not surprise me that food web recovery can be unstable because following mass extinctions, many niches are temporarily filled with the more abundant survivors, such as how ferns and sporomorphs become more abundant before other species of plants are able to recover. Trends like this are likely to mess with the food web recovery, therefore it takes a long while for the web to resituate following a mass extinction.
Robertson:
ReplyDeleteAfter the Chicxulub impact it was very important for organisms to find shelter for many reasons. First organisms needed to move underground to escape radiation and the shock in temperature coming off the impact. Organisms also needed to escape the soot, fires, and acid rain caused by the intensity of the impact. In class and after reading, it can be assumed that the impact was so large that a double impact would not have affect the large comet impact. The survival strategies would have been to burrow low enough to not be affected by the impact. Avain groups would have also needed to leave their habitats to burrow. Living in water was successful for organisms because the water would have blocked out a lot of the harmful radiation.
Schulze:
I do not believe that any of the other four hypothesis would have contributed to the extinction because of the aftermath of the large impact. I think the radiation from the impact was what affected organism the most. The radiation was so strong organisms would not have been able to out run it and larger animals would not have been able to burrow or escape it. I believe the wild fires would have been somewhat constrained to the immediate area around the impact. Even though these fires were local they were still very widespread.
Wilf:
I think with learning more about the organism that went extinct we can create a food webs. The teeth of these organism would be most important because we can see if their diets were more based on plant or meat eating. No, it did not surprise me that food web construction can be unstable. Since we are not sure exactly what organism went extinct we can only guess about the food web until we find more fossil records.
Robertson et al.
ReplyDeleteIt was important for organisms to find shelter right away from the Chicxulub bolide impact because it caused so much dust, acid rain, soot, and very high temperatures around the globe. If organisms did not find shelter quickly, they would not be able to survive from the bolide impact because it would kill most of them due to not being able to adapt to the conditions. They were too extensive for organisms to survive. Living in water was a good way of surviving because the impact caused all these factors in which being a terrestrial organism made it harder to survive, but being able to live in water helped because the effects were not as drastic on the organisms and they could protect themselves from the dust and soot.
Shulze et al.
I would think wildfires would be more localized from the Chicxulub bolide impact. As the bolide hits the globe, I believe it would cause more wildfires in the immediate area of where it hit within a certain radius. There could have been wildfires from smaller pieces of the bolide breaking off and hitting other places, but from the immediate impact of Chicxulub, I think it would only cause the localized wildfires because the radius of impact can only go a certain amount creating those fires. The wildfires in a sense could become widespread if they continuously kept spreading over the land.
Wilf et al.
I do not find it surprising that this paper found food web recovery unstable. Putting a food web together after a mass extinction would make it very hard for that organism who survived because they would have to adapt to so many changes. Even though the organism survived, doesn’t mean that the rest of the food web it interacted with was able to survive in a mass extinction creating lots of difficulty in this situation.
Robertson et al.:
ReplyDeleteDuring the first few hours, there was a short term infrared event. This was stressful enough for all organisms that it killed all nonmarine macroscopic organisms that were out in the open. Organisms that were sheltered, such as in soil, under rocks, or in water, had a better chance at surviving. Spherules were abundant enough to increase temperatures from 800-1100K in the first several hours, creating a huge heat pulse. Finding shelter would have been crucial because the earth was literally on fire.
Survival strategies among the surviving terrestrial and avian groups were pretty similar. Small mammals were able to burrow underground to remain cool. Soil is a great insulator absorbing most of the heat in the first 10 centimeters. They were also able to briefly enter the water in an attempt to remain cool. Dense marsh vegetation would have provided some shelter for birds because they probably didn’t burn completely. But many birds sheltered in rock piles or insulated cavities, such as burrows. This allowed escape from extreme thermal stress.
Living in water was a successful strategy because water is a great insulator. Most of the energy from the IR radiation dissipated in the top few micrometers. This means that the ocean water did not heat up. Some heat might have been able to make it down the water column because of turbulence or wind-driven currents, but it is nothing compared to the heat felt on terrestrial land.
Shultze et al.:
Choosing one proximal cause that affected organisms on land or sea the most is difficult. I believe that all the causes together created havoc for the organisms. Earthquakes of magnitude greater than 11, tsunamis and ejected material probably affected terrestrial animals more than ocean ones. Animals on land can’t hide as easily as ocean creatures. The animals that were to big to burrow would have had to feel the effects of all these head on. Ocean animals might have been affected by tsunamis, but I think the dust in the sky would also have an effect because it would’ve changed the climate. The Deccan flood basalt volcanoes would definitely had an impact on all creatures. These would have released chemicals into the atmosphere, raised global temperatures, and dispersed soot and dust around the world. With all the dust remaining in the atmosphere, this caused other problems such as global cooling and acid rain.
I believe the impact could have caused global wildfires. In the Roberson et. al. paper, it discusses how extreme the IR radiation was and how it warmed the world up. Such drastic warming mixed with the energy released in the shockwave from the impact of the meteorite, I think that would have been enough to cause fires anywhere.
Wilf et al.:
I don’t find it surprising that food web recovery can be unstable. A lot of factors have to be going right in order for a food web to recover. The natural world is like a pyramid, one thing has to be present, which gets eaten by something bigger, which then gets eaten by something bigger. If some parts of the tier gets wiped out, then other parts become unstable. Things are no longer eating or getting eaten and it throws off the entire ecosystem. It would make sense that it would take years in order for food webs to recover, and they will never be able to recover to the same degree as they were before because things get extinct. Organisms have to be willing to adapt in order to survive, which is crucial after a mass extinction, where a lot of things perish.
Robertson
ReplyDeleteThe first few hours following the Chicxulub bolide impact were when the atmosphere/environment would start changing for organisms farther outside of the impact range. They would need to burrow down or hide in water sources to survive the shock wave, radiation, and possibly forest fires. With all of this happening in a span of a couple hours, organisms would have to find shelter as quickly as possible to survive. There would also be so many chemicals sent into the atmosphere, that breathing could also cause severe consequences. If an organism goes underground or in water, they at least have a larger barrier from the toxic air and the changing environment.
Schulze
I believe that volcanism was the main source that affected organism both on land and in the oceans. With volcanism, there would have been lots of chemicals and ash sent into the atmosphere. This would make the air toxic and not allow as mush sunlight to pass through. This would slow down or stop photosynthesis in plants and create warmer temperature all around the globe. Marine life and terrestrial life would have to deal with a larger change in their original environmental conditions in a short time span, that we would see mass extinctions happening on both sides.
Wilf
It did not surprise me that food web recovery was unstable. With mass extinctions, almost all niches in a habitat or environment will be affected. With even just one loss to the food chain cycle, all other organisms would have to try and find a source to replace that missing piece. In most cases, there is not enough time to do so and numbers of that population start to dwindle down and leave no survivors.
Robertson:
ReplyDelete1. After the impact, the organisms would need to find shelter for a multitude of reasons, namely the shock wave and radiation. Not only that but there would be forest fires and dust kicked up from the impact, earthquakes, and so on and so forth. Safety first.
2. A double impact could have made it worse, but since the initial impact was so enormous and devastating, the second impact would have had to be massive as well to not be overshadowed by the first. So a double impact probably would not have been that much worse.
3. The IR blast hurt the terrestrial organisms because they had less protection than the marine organisms. They were exposed to the radiation in full effect, being on land where the impact occurred. So the radiation damage was unavoidable for the terrestrial organisms, and so they were devastated by it.
4. Some of the survival strategies of terrestrial organisms was to seek shelter or even get underground to hide from the heat wave and IR blast.
5. Living in water was beneficial because the water provided a buffer between the organisms and the initial IR blast, it also protected from fires and earthquakes, LIPs, and so on.
Schulze:
1. I don't think any of the four alternate hypotheses seem accurate, as a bolide of that size definitely seems like the most probable cause for the mass extinction. While the evidence can make the theory of the bolide impact seem fuzzy, the bolide impact itself and the crater evidence is definitely the "smoking gun" of the theory. The basalt eruptions sure could have helped, but the impact is just too concrete when it comes to evidence.
2. Terrestrial: the radiation wave and the heat waves. Marine: As usual, anoxic events coming from acid rain, dust, etc.
3. I believe the impact definitely could have caused global wildfires. I doubt every square inch of the land was a firey inferno, but without any sort of containment system for the fires, they could have spread incredibly fast and over a large range of land. These days with fire departments and planes and helicopters we can contain wildfires, but those obviously did not exist 65 million years ago, so the fires were basically free to spread.
Wilf:
1. Knowing what species went extinct and what species survived would be useful, as well as more about the species themselves and what sorts of things they ate. Knowing that a species that ate only a specific kind of plant went extinct while a species with a ore diverse diet, for example, would give a good idea of what sorts of plant life were around if species A survived but species B went extinct, or the other way around.
2. I am unsure if I understand the question but I would suggest that localized diversity becomes "atypical" when something happens that basically makes a niche become available and empty so something occupies the niche that someone wouldn't expect to be there?
3. No, I was not surprised at all that food web recovery can be unstable. When mass extinctions happen, niches get wiped out and filled quickly through adaptive radiation, such as ferns and sporophores taking over whenever there was a huge loss of trees and other large flora. This changes the food web of the region of course, and it might not even recover in the first place- it might just change to something that didn't exist before the event that wiped it out.
Robertson et al. 2004
ReplyDeleteIt was essential for terrestrial organisms to shelter during the first few following the Chicxulub bolide impact because direct skin exposure to the infrared pulse would have resulted in the absorption of intense radiation. This would have fatal effects on the organism’s nervous system. Two craters/asteroids have been identified that could have been companion bolides to the Chicxulub: a 2-km-diameter asteroid and a 300 km diameter crater. The 2-km asteroid would not have likely resulted in anything other than regional influences, but the asteroid which created the 300 km crater could have added significantly to the devastation wrought by the Chicxulub bolide. However, this larger asteroid has not been further investigated, and is not yet well supported. The energy and power provided by the bolide in its first few hours of infrared radiation would have been too much for organisms to handle and would have had lethal impacts on non-sheltered organisms. Mammals and birds that survived all participated in some type of sheltering, whether it was in soils, underground, deep in rock piles, or in holes in trees. Additionally, organisms that spent much of their time deep underwater would not suffer as much from the intense radiation and would have likely survived.
Schulze et al. 2010
I do think that the Deccan flood basalts could cause an extinction event, but I doubt it would be significant enough to qualify as a mass extinction. The lack of sunlight seems to be the proximal cause which the authors most emphasize in the paper, discussing how phytoplankton suffered largely due to the reduced sunlight. I think that would be the most significant proximal cause from the impact. I’m not convinced that the impact caused global wildfire, though I am certain it caused significant regional wildfire.
Wilf et al. 2006
Analysis of stomach contents is another potential way to examine food webs. For example, but analyzing the amount of carbon-13 an organism has in its stomach contents, one can determine a sort of prey base for that organism. This, however, would likely be unsuccessful for fossilized remains. A simple observation of what fossilized remains are found in fossilized stomach would be useful for constructing a food web. Biodiversity is hugely dependent on environment, and I believe can be directly related to the amount of biological niches any particular environment provides. Therefore, regions with large amounts of biological niches will correspond to higher biodiversity.
Certain traits would have been essential for surviving a large bollide impact. These traits included anything that enabled you to be sheltered from some of the many kill mechanisms that would have occurred shortly after the impact. Although these traits would have helped you survive the initial onslaught of things like fire and IR it did not guarantee your long term survival. For birds for example we know that the clade of opposite birds which was the most diverse at the time disappeared after the Kpg. Some theories suggest they were very diverse with many specific niches and were not able to survive long term after the impact but modern bird clades specialized on seeds which would have been around long enough for them to continue eating long after the bollide struck the earth.
ReplyDeleteDouglas S. Robertson et al. 2004
ReplyDelete1) Terrestrial organism needed to find shelter since the environmental they lived in did not provide a natural buffer of radiation or heat so finding shelter the first few hours would protect them from these disasters.
2) A double impact would have caused the duration of effects to last longer.
3) The IR flux would have “fried any organism that did not find shelter through the absorption through there tissues or the fires it caused.
4) The way some mammals survived was by burrowing or living short term in aquatic environment.
5) It’s provided a heat barrier and other protection from the initial effect of the impact
Schulze et al. 2010
1.I don’t think I find any of them more compelling that the current popular theory. I think this is due to it being more supported by the evidence even though there are some problems with this theory I think so far it’s the best one and closes to what happened.
2. I think sulfate emissions affect both side the most as acid rain seemed to be the cause that could effect both environments significantly. For land I believe the radiation spike would be the most detrimental globally while in sea I think the shut down of primary production would affect the food chain dramatically especially if this was not a short episode.
3. I think the impact would have caused regional fires rather than global fires as the area near the impact would only have ignition of the forest as I don’t believe these could spread to become global fires but the case of global radiation causing the fires does sound promising.
Wilf Et Al. (2006)
1) I think looking the teeth in addition to looking at where these are found in relation to plants and other food interactions. This though would be a lot of data to have to sort and organize and would be mostly guessing
3) I’m not surprises that reconstruction was difficult and not that great as the fossil record is already difficult to interpret events from so interactions between organism must be much harder as soft tissue is rarely preserved
As with most, if not all, of the comments above, I believe that searching for shelter either by burrowing or in the water would be crucial to surviving the first few hours of the Chichulub meteor impact. Organisms would need to find shelter in order to escape the global radiation and fires in order to have even a chance of surviving later. In addition, regional effects such as earthquakes and tsunamis would have added extra obstacles to the survival of animals found in North and South America. Having a smaller body size would also help an organism's chances of survival, because they could likely get to shelter quicker. Larger organisms would not have the time to find adequate shelter and their size would limit what shelters would be available to them.
ReplyDeleteAn interesting question asked about the Robertson et al. paper was about the effect of a double impact. I believe that a double impact to the same region would magnify the effects there and cause the catastrophic events to last longer. The global radiation and fires would have a longer duration than if there was only one bolide impact. I think it is especially interesting to think about what would happen if there were two bolide impacts on different parts of the earth. The Chicxulub bolide impact affected North and South America regionally, but if there had been a second impact in Asia for example, I think that would have an even more devastating effect on the chances of survival for species.
None of the four alternative hypotheses listed in the Shulze et al. paper were very compelling on their own. I believe that the Deccan traps spewing basalt into the atmosphere could have helped play a role in the K-Pg mass extinction, but I don't believe we can say that it was the only factor. I don't believe that we can reasonably say that the Chicxulub impact occurred significantly before the K-Pg boundary because almost all of the evidence that has been collected for this mass extinction points otherwise. Maybe the combination of Deccan traps and the bolide impact released enough sulfur and nitrogen to cause global cooling and a shutdown of photosynthesis, but I don't believe that the Deccan traps alone are responsible.
I think I would expect some variation in the rates of recovery, especially at different sites. The K-Pg mass extinction was a global extinction with global consequences, but I think there would be different recovery rates based on the degree of destruction. I think it is reasonable to say that North and South America were hit especially hard by the impact and might have a greater degree of destruction than an ecosystem found across the world. That is not to say that ecosystems across the globe were not all devastated; they were, but I believe that North and South America would have the additional burden of tsunamis and earthquakes to cause further upheaval in the ecosystem. Overall, I think the use of insects as markers of recovery is very intelligent because they rely on primary producers to flourish. If the primary producers are recovering, then primary and secondary consumers shouldn't be far behind.
Robertson
ReplyDeleteSheltering was key in avoiding the IR radiation the emanated from the impact, avoiding immediate death as a result of the impact. A second impact, when examining short term effects, would not have had too much of an impact, as the heat weave and its thermal impacts was the immediate kill mechanism, and two happening at once wouldn't have increased the thermal heat wave (which was already devastating enough that increases wouldn't have made too much of an impact) enough to incinerate more organisms. Without sheltering, the IR wave caused an immense thermal disruption that, in fauna, incinerated directly exposed skin, and caused thermal radiation to be absorbed fatally into the nervous system. Most aboveground flora was instantly incinerated as well. Surviving terrestrial and avian groups needed to subsist for a long time with little to no food either due to aestivation or low metabolic rate, express sheltering behavior in soil or rock, and subsist on a preferably omnivorous diet. Water has enough opacity and resistance to changes in heat that it acted as a barrier between organisms living in it and the IR wave outside.
Schultze
While the other four hypotheses may have contributed to the general upheaval of the KPg extinction, they would be minor contributors (except the volcanism, which could have sustained effects) in comparison to the impactl, which would have instantly altered entire ecosystems by obliterating any non-sheltered fauna. Land organisms would have been proximally affected by the "nuclear winter" effects, the global cooling that could have persisted for decades due to changes in the atmosphere. Water organisms would have been proximally affected by the influx of heavy metals and toxic elements into their environment. Its likely there were global wildfires, as the debris that was launched into the atmosphere came back down at extreme temperatures and caused wildfires wherever they landed.
Wilf
It would be valuable to look at anything that could give clues to where on a food web a species was, such as tooth morphology, and which species went extinct, in order to determine which niches were empty, and which species had lessened access to food, such as a strict herbivore being unable to access its only food source. Atypical localized regions of diversity most likely occured as a result of the differences in populations of surviving organisms and their corresponding environment, and their differences in adaptation as they struggle to survive in their changed habitat. The food web is predictably unstable, as the remaining organisms are under a great deal of selective pressure and will radiate and adapt in response to those pressures, and especially competition between species as they emerge at different times into the niches would cause constant flux in the food web.
Robertson et al. (2004)
ReplyDeleteThe reason terrestrial organisms should’ve found shelter during the first few hours is because of the IR flux that spread over the landscape that incinerated most terrestrial species above ground. A double impact I believe would have created more projectiles dispersing from the actual location because the primary asteroid would’ve sent projectiles and a massive shockwave that would’ve cause the second asteroid to detonate, or explode prematurely, causing projectiles to spread over a larger geographical area. The reason the IR flux was responsible for being the kill-mechanism on terrestrial organisms within the first few hours is because high temperatures that could penetrate several feet in the ground cover a wide location, followed by forest fires that ignited as the IR flux passed. Some of the survival strategies of the surviving terrestrial and avian groups were the ability to dive underwater or borrow beneath the ground to avoid the IR flux. The reason living in water would’ve been a successful strategy for survival after the impact would’ve been because of the loss of habitat, toxic gases in the air, and high Nox levels. What I think would be interesting to understand about the events that occurred during this impact would be the time frame of when this impact occurred, was it during the day when the nocturnal species were burrowed, or was this a time when some species were hibernating. The reason I ask is because many species hibernate including some birds. Hibernating also decreases body temperature, and oxygen level so I would ask the question could this be a possibility?
Schulze et al. (2010)
I think the evidence of a double-impacted described in Robertson (2004) provides some credibility to the large spread of forest fires that ignited during this time. As for the Deccan flood basalt eruption, it may have be happening prior to the impact but the earthquakes, and the ejecta from the asteroid may have increased the severity of these eruptions which in return created the increase of sulfur, and carbonates, this would coincide with the Wilf (2006) article that states high levels of tannin contents were found in the Castle Rock flora, which could indicate acid rain and decomposition organic matter may have played a role in the high tannin contents found in the flora. So, to answer the question if I would find any of the four contributors to the K-Pg mass extinction I would have to say, I think they all played a role in the widespread extinction. It may not have happened with in the same day as the Chicxulub impact, but they all played a vital role in the extinction of many species.
K-PG: THE DEMISE OF NON-AVIAN DINOSAURS AND RISE OF MAMMALS
ReplyDelete1. It was important for terrestrial organisms to find shelter during the first few hours after the impact of the KPG, because of the intense shock waves and overwhelming heat, radiation, and forest fires produced in a substantially large circumference around the site of the impact. If organisms were going to be able to survive these harsh conditions they needed to be protected underground or underwater. This gave an advantage to smaller marine and terrestrial organisms who could easily take shelter under both forms of protection and it was in their instinct to do so. Larger organisms were most likely not burrowers by nature and therefore would have to sense to take shelter during the impact.
The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary
1. I think that the Decan flood basalt eruptions would have defiantly contributed to the mass extinction simply because there is so much evidence that they were occurring around the same time as the impact at the KPG boundary. I think that it is likely that the impact somehow caused the eruptions and therefore the eruptions were just many of chain devastation events to life on earth at the time.
Decoupled Plant and Insect Diversity After the End-Cretaceous Extinction
3. At first it did surprise me that recovery of a food web would be sporadic and unstable across the globe, but that is based on my previous general idea that mass extinctions wipe out all forms of life ( I am premed bio major so I haven’t given much thought to past life or extinctions at all) . However, after giving greater thought to mass extinctions and thinking of them in terms of what organisms survive versus what organisms die out I can see that the life that is left after a devastating event such as the impact at KPG would be not uniform. Therefore, any recovery of life and food webs afterwards would not recover in a uniform fashion either.
SURVIVAL OF THE CHICXULUB ASTEROID IMPACT AND MASS EXTINCTIONS
ReplyDeleteSurvival in the first hours of the Cenozoic
By: Douglas S. Robertson et al. 2004
1)It was so important for terrestrial organisms to find shelter during the first few hours following the Chicxulub bolide impact because they needed to avoid all of the effects the bolide created when it hit (high temperatures which ignited fires, thermal radiation pulse, soot, etc).
2)A double-impact would have affected the outcome of the Chicxulub impact in a more catastrophic way. The magnitudes of the earthquakes, shockwaves, tsunamis, etc. would have been increased and could have caused more species to become extinct.
3)The IR flux was responsible for being the kill-mechanism of non-marine, terrestrial organisms in the first few hours after the Chicxulub impact because the radiation incinerated any organisms within range.
4)Some of the survival strategies of the surviving terrestrial and avian groups were that they were able to fly to other areas in which were not affected by the bolide, they could hide in caves/crevices or borrow underground, escape into the water, etc.
5)Living in water was a successful strategy for survival immediately after the Chicxulub impact because they were able to avoid the impacts on terrestrial land such as the fires/intense heat as well as the atmosphere (full of ash/soot).
The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary
Schulze et al. 2010
1.Personally, I don't find any of the four alternative hypotheses to have contributed to the K-Pg mass extinction more than the proposed theory because this theory has evidence to support what happened and is generally agreed upon within the scientific community as the best explanation for what happened.
2.The proximal cause from the impact that I think affected organisms on land or sea the most was probably the IR radiation flux because it would have had a global effect in which would have killed all sizes of organisms and reached the most. I also think the release of Co2/other compounds from soot would have had a drastic effect because all organisms breathe/take in the compounds form the atmosphere.
3.Yes, I do think the impact would have caused global wildfires because when the bolide hit, there was a shockwave/pulse in which traveled far and the temperature would have increased dramatically which would make fires more likely and the earthquakes would have knocked down trees, etc.
Decoupled Plant and Insect Diversity After the End-Cretaceous Extinction
By: Wilf Et Al. (2006)
1) Other valuable information that I think might be important towards reconstructing a food web after a mass extinction could be the anatomy of the organisms (teeth) as well as looking at the regions in which they were found as well as the types of plants to formulate how the two interacted with each other.
2) I think atypical localized regions of diversity occur as a result of the differences in populations of surviving organisms with regards to how they adapted after the bolide hit and how they diversified after the event.
3) No, it didn't surprise me that this study found that food web recovery can be unstable because the bolide hit in a certain place/angle on Earth and did not have the same affect for organisms across the whole globe and the magnitude of all the cascading effects would vary depending on how far away the impact was.
"Why was it so important for terrestrial organisms to find shelter during the first few hours following the Chicxulub bolide impact?"
ReplyDeleteThe bolide impact had many catastrophic regional events that would have cause immediate death to the organisms in that area. The top regional events that would have been devastating to life where the shock waves and fires from the initial impact, the tsunamis that would have been massive and relatively widespread, and the massive earth quakes that would have followed the impact. These are the reasons that it was imperative for living creatures to find shelter and quickly. The water would have acted as a type of shelter for some of the marine animals, but really it depended on how deep they were able to dive to and how far away from shore and the impact they were. Burrowing would have been another means of shelter if the animal was able to burrow quickly and deep enough, and was not in the pathway of one of the huge tsunamis or earth quakes.
"Would you find any of the four alternative hypotheses to have contributed to the K-Pg mass extinction? Why or why not?"
I do think that some of the other hypotheses contributed to the mass extinction. However, I do not think that any of them are the ultimate cause of the extinction. One of the hypotheses that is still in debate today is whether or not the Deccan traps were the ultimate cause of the extinction vs. the bolide impact. I think that the Deccan traps played a large role in the extinction rates due to what we already know about what the LIP events do to the the carbon and sulfur concentration in our atmosphere. I do not think that these changes are enough to cause the major changes that we can see when looking at the carbon changes and temperature changes at that time. There is also the matter of the massive uranium concentration spike that we see in sedimentary rock samples from the time of the K-Pg mass extinction. I think that there is always multiple layers to any of these huge events that happen in our world's history, in this case though I would agree with Schulze in saying that the bolide impact was the ultimate cause of this specific mass extinction.
Robertson et al. 2004
ReplyDelete1.) It was important for terrestrial organisms to find shelter during the first few hours following the impact because of the initial blast. The initial impact would have created horrific shockwaves, Tsunamis, and incendiary forces. If you did not find cover initially, you would have drowned, vaporized, and possibly killed by the sheer force of the blast.
2.) A double impact would have more than likely intensified the Chicxulub impact.
3.) Unless you had been a marine organism or had found shelter, you would have been exposed to the radiation. Exposure to radiation kills. Marine species were provided some cover by the water, which would have negated the amount of radiation, they were exposed to.
4.) The survival strategies would have been finding shelter and possibly scavenging for food.
5.) Simply, aquatic species were provided some protection from the heat wave and radiation. However, regional species to the blast would more than likely have suffered from the shockwave as well as the Tsunamis that followed.
Schulze et al. 2010
I believe the bolide impact is the most prominent cause of the K-Pg mass extinction. However, I do believe the Deccan flood basalts may have contributed as well. The reason being is that the impact of the bolide may have rippled across the Earth's crust which may have allowed for increased volcanic activity, through weak areas in the crust. A single event does not seem likely, especially an impact. I do believe that the impact did cause other geographic forces to occur which aided in species extinctions.
2.) I believe the shock wave affected organisms the most. It is similar to a grenade. You do not have to catch shrapnel to die. If you are close enough, the amount of pressure from the explosion can kill you.
3.) I think the impact indirectly caused wildfires. This is going back to the rippling effect I explained on the first question. The impact could have increased volcanic activity, around the globe, which led to the massive outbreaks of wildfires.
Wilf et al. 2006
1.) Analyzing the surviving organisms as well as the deceased organism can help reconstruct a food web. By doing this, we can see what animals fed on whom and organisms proliferated due to a lack in the species that preyed on them.
2.) I think it was because the dissipation of primary species in those regions allowed for atypical species to flourish. The loss of one species in an area, allows for another to inhabit it. Especially species that were minimized by an abundance of another.
3.) I do not find it a surprising. Our current fossil record is inconsistent and incomplete. There is always the probability of missing important information. The problem with analyzing past food webs is that if you do not have enough species, or even missing a few key species, the food web could be problematic.
I personally think that some combination of the Chicxulub crater impact, thermal radiation and massive amounts of soot in the air are to blame for the wide mass extinction of the dinosaurs, and the dawn of the mammals. Many of the dinosaurs were large and probably didn’t know what to do when this catastrophic event took place leaving them exposed and vulnerable to die off. I don’t think it was in the T-rex’s mind set to find shelter in a cave or underground much less have a place large enough to fit in. Even if he/she did find shelter, in order to carry on the species there needed to be the opposite sex in order to reproduce. Thus small mammals and other size ranges existing at this time had an advantage. The Chicxulub impact affected everything alive. With that being said many terrestrial organisms needed to seek shelter from the blast of massive radiation, heat wave, soot and wide spread fires that were present during this time.
ReplyDeleteThe first few hours of this impact were incredibly hot with raging fires, acid rain, dark air particulates, and intense sun exposure. The beginning of the impact was the most extreme time of its destruction, so species that could wait-out this period underground or within structures were more likely to be able to survive the following less intense disruption.
ReplyDeleteTwo impacts would have generally had even more intense destructive ability and the initial extremity could have likely been extended. If the impacts were some time apart, this may have resulted in the die-off of species that survived the first impact as they may have left shelter during the less-extreme events and then were exposed to another impact.
Such a massive flux of radiation would have essentially burned away any exposed species (marine life deep in water was shielded from most of this effect).
Burrowing and underground dwelling, having robust and deep/expansive vegetative roots would have been helpful for survival in terrestrial species. Avian species more likely survived if they were coastal because of the shielding capacity of the ocean.
Living in water would shield marine species more effectively than terrestrial characteristics would against radiation. Light can only penetrate so deeply into water, but on land it would penetrate quite directly and intensely on terrestrial species.
I most believe that the Chicxulub impact could have caused eruptions in the Deccan basalts. This could explain the detrimental atmospheric changes such as sulfuric acid rain and dust and light blockage.
On land, species would have been most affected by the intense heat and radiation because, besides limited shelter, they have no defense against it. For ocean life, acid rain caused by sulfuric volcanic eruptions would have been detrimental to marine life in the changing of ocean solubility and pH.
I think fires would be world-wide only if burning-hot or ignited ejecta were dispersed world-wide which is not really known. I would guess that the fires were a only subsidiary contribution to the impact’s damage.