From TOHOKU UNIVERSITY
A new hypothesis on the extinction of dinosaurs and ammonites at the end of the Cretaceous Period has been proposed by a research team from Tohoku University and the Japan Meteorological Agency’s Meteorological Research Institute.
The researchers believe that massive amounts of stratospheric soot ejected from rocks following the famous Chicxulub asteroid impact, caused global cooling, drought and limited cessation of photosynthesis in oceans. This, they say, could have been the process that led to the mass extinction of dinosaurs and ammonites.
The asteroid, also known as the Chicxulub impactor, hit Earth some 66 million years ago, causing a crater more than 180 km wide. It’s long been believed that that event triggered the mass extinction that led to the macroevolution of mammals and the appearance of humans.
Tohoku University Professor Kunio Kaiho and his team analyzed sedimentary organic molecules from two places – Haiti, which is near the impact site, and Spain, which is far. They found that the impact layer of both areas have the same composition of combusted organic molecules showing high energy. This, they believe, is the soot from the asteroid crash.
Soot is a strong, light-absorbing aerosol, and Kaiho’s team came by their hypothesis by calculating the amount of soot in the stratosphere estimating global climate changes caused by the stratospheric soot aerosols using a global climate model developed at the Meteorological Research Institute. The results are significant because they can explain the pattern of extinction and survival.
While it is widely accepted that the Chicxulub impact caused the mass extinction of dinosaurs and other life forms, researchers have been stumped by the process of how. In other words, they’d figured out the killer, but not the murder weapon.
Earlier theories had suggested that dust from the impact may have blocked the sun, or that sulphates may have contaminated the atmosphere. But researchers say it is unlikely that either phenomenon could have lasted long enough to have driven the extinction.
The new hypothesis raised by Kaiho’s team says that soot from hydrocarbons had caused a prolonged period of darkness which led to a drop in atmospheric temperature. The team found direct evidence of hydrocarbon soot in the impact layers and created models showing how this soot would have affected the climate.
According to their study, when the asteroid hit the oil-rich region of Chicxulub, a massive amount of soot was ejected which then spread globally. The soot aerosols caused colder climates at mid-high latitudes, and drought with milder cooling at low latitudes on land. This in turn led to the cessation of photosynthesis in oceans in the first two years, followed by surface-water cooling in oceans in subsequent years.
This rapid climate change is believed to be behind the loss of land and marine creatures over several years, suggesting that rapid global climate change can and did play a major role in driving extinction.
Kaiho’s team is studying other mass extinctions in the hopes of further understanding the processes behind them.
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One possible problem with this particular hypothesis is that they state:
I understood that the big oil fields of Mexico were composed of debris that filled the Chicxulub crater. I.e. they post-dated the impact and that the region’s “oil-rich” character is a consequence of the event. The unusual origin of the carbonate breccias is what gave them the high porosoity and high permeability that make the Cantarelli oil field so productive.
Here’s another thing that bothers me, as someone who has spent a lot of time looking at rocks and trying to learn what they can tell you.
There’s this famous photo of the Alvarez’s standing at a rock face where the K-T boundary is exposed. It’s an unbroken sequence of what look like shallow marine sediments. The transition from Cretaceous to Tertiary has presumably been determined by palaeontology.
The sceptic in me says: if a 10 km diameter asteroid or comet impacted the earth, the seismic activity would have been colossal, beyond anything we can visualise from our personal or vicarious experiences.. There should have been world-wide tsunamis that would (ought to have?) disrupted the process of calm, orderly sedimentation in shallow seas. Some scouring of subjacent layers with redeposition, some coarser material washed in from nearby land areas, something – anything – that disrupts what appears to be an uninterrupted sedimentary sequence.
Marine sediments would not necessarily show much evidence of land-based extinction, but a lot of marine species went extinct at the same “time” (especially ammonites). If all the ammonites died in a very short interval (as postulated in this “soot” hypothesis), wouldn’t there be a sedimentary layer with an exceptionally high number of ammonite shells at the K-T boundary? As opposed to what one might expect if the “Deccan Traps caused the extinction” hypothesis were correct, which would have resulted in a progressive decrease in ammonite shells as the boundary is approached from below. Which seems to be the case.
Not saying that the hypothesis is wrong, just that the postulated event is so apocalyptic that there ought to be more evidence of it in sedimentary rocks laid down at the time. More than just a bit of soot and an enrichment in iridium.
Geology is a very inexact science, far more than most of its practitioners care to admit. Too often, hypotheses that are intellectually attractive, are based on scattered bits of hard evidence (e.g. chemical and isotopic analyses) dropped into a matrix of generally soft, rather pliable evidence (looking at the rocks), without adequate consideration of possible alternatives.
I really like that term I just came up with “pliable evidence”. I think I’ll be using it a lot from now on. In reference to Climate “Science”.
” There should have been world-wide tsunamis that would (ought to have?) disrupted the process of calm, orderly sedimentation in shallow seas.”
There was. There are lots of sites with severely disrupted or chaotic stratification for thousands of miles around Chicxulub, but for studying the impact one searches for deep-sea sediments deposited far away in distant oceans, because that is where you will find continuous deposition and an intact fallout layer.
And remember if all ammonites were killed by Chicxulub, that means that one standing crop was deposited in perhaps a few weeks. Lets say that the average lifetime of ammonites was (optmistically) 50 years, that means that those ammonites were deposited in one year rather than in fifty. That is an indistinguishable difference in the marine fossil record.
The impact would have created a massive tsunami. However tsunamis can’t cross continents.
Sometimes the truth is right in front of your nose and you don’t see it.
Take the dinosaur extinction. Every creature we call dinosaur went extinct except those who learned how to fly. Until recent times, flightless birds, aka dinosaurs, lived on islands. As soon as the mammals showed up, human, rats, and dogs, those dinosaurs went extinct.
Does this suggest a hypothesis to anyone to explain the dinosaur extinction? The cause of their extinction of course is they have to incubate their eggs and otherwise guard their nests from predators, making them and their ground nests highly vulnerable to predation. Reptiles, which can bury their eggs (hide them) and leave the next unattended, have survived. Just like mammals, the dinosaurs had to take to the trees to survive.
Next question.
The question is why the mammals didn’t wipe out the dinosaurs earlier. Placental mammals appeared after the disappearance of dinosaurs and marsupials are just as old as dinosaurs. And ammonites didn’t get wiped off the map by mammals.
Its more a question of how a family of organism has the potential to evolve into a better competitor but doesn’t seem to get a foot in the door until the population of its competitors is decimated. It happened to a family of reptiles, the synapsida, that ruled the land but died out shortly after the previous Pt event leaving just a small population that couldn’t compete with the offspring of other reptiles, namely the dinosaurs. They were all eventually wiped out except the ancestors of mammals.
It could be that marsupials were held back by preditation, then it wasn’t so much the die off but the abundance of carcasses that took the pressure off mammals and allowed the population to explode to numbers that kept the dinosaurs from bouncing back.
Dinosaurs had been preying on each others eggs for millions of years before the first placental mammal showed up.
It’s all about surface, not universal, gravitation changes around the Earth. At the Triassic-Jurassic boundary a rapid increase in surface gravity on Pangea was responsible for the extinction of the crurotarsi, which held the dinosaurs in check. The reason for their extinction? Almost all of them had a splayed leg structure unlike the vertical leg structure of the dinosaurs which would have been a major handicap when surface gravity increased.
The ammonites went extinct because the increase in surface gravity affected all marine creatures that moved up and down in the water column. An increase in surface gravity would increase the water pressure per unit depth. The nautilus’s body was better able to deal with this challenge; that’s why it still exists.
All of this is explained by the Gravity Theory of Mass Extinction.
There are some ideas that are just too dumb to die.
And some people too!
Back in the late sixties engineers showed that with the sudden improvements demanded by the clean air acts the original Stevenson screen was no longer adequate for producing accurate results and would produce anything up to a degree higher than actual ones compared to the air quality at the turn of the century.
Yes this was done with actual hardware not computers but it really did warrant proper examination by scientists who were simply not interested in the nuts and bolts of data acquisition.
Why is this effect so important if it is so irrelevant when considering climate change I wonder?