Incoming: The Chicxulub Impactor, Part 5 ― Other Theories & Other Extinctions
By Stephanie Osborn
Some statistical studies indicate that, based on the fossil record, most of the major dinosaur groups were already declining during the Late Cretaceous, though certain herbivore groups appear to proliferate during this period.
The researchers who performed these studies indicate that the dinos’ inability to “replace extinct species with new ones” left them vulnerable to extreme stressor events, such as a major impact.
Not everyone agrees with the studies.
The Deccan Traps were a non-explosive form of supervolcano located on the Deccan Plateau of west central India, and even today are generally considered to be one of the largest, if not the largest, volcanic feature on Earth. A volcanic trap consists of one or more long cracks, parallel if multiple, from which low-viscosity basaltic-chemistry lava extrudes. Due to the low viscosity of the melt, eruptions are rarely explosive, but the lava is “runny” and fast-flowing, and traps extrude great quantities of it―anywhere from tens to millions of cubic kilometers of lava. (For more information, see Kiss Your Ash Goodbye: The Yellowstone Supervolcano, which discusses traps.) And the Deccan Traps were huge, at about three-quarters of a million cubic MILES of lava extruded.
Extinction would have occurred due to the hypothesized release of copious ash and carbon-and sulfur-compound aerosols into the air, blocking light and reducing photosynthesis in a volcanic winter before causing a runaway greenhouse effect after the ash settled.
But since traps are generally not highly eruptive, getting the ash (and maybe the gases) high enough into the atmosphere to have a GLOBAL negative effect would be difficult.
More, the clay boundary layer doesn’t occur DURING a trap-eruption layer, but BETWEEN them, indicating the Deccan Traps were not erupting at the time of the extinction.
This hypothesis is no longer widely accepted.
Several other known craters have similar geologic ages, and a couple of additional
hypothesized-but-undiscovered craters may add to the tally, too.
When we reconstruct the tectonic plates as they would have existed at the time, all these form an equatorial swath; some therefore propose that Earth was hit by a recently-broken family
of bodies akin to Comet Shoemaker-Levy 9.
During the last age of the Cretaceous Period, there seems indisputable evidence that the sea levels fell by a substantial margin. Earlier layers depict the signature of sea beds, while later layers are obviously dry land. There is no obvious explanation for why; the current theory is that the mid-ocean ridges (a spreading tectonic plate boundary, basically elongated volcanoes) stopped erupting and sank under their own weight.
But that wouldn’t have affected deep-water organisms or land creatures at all. Yet all of these were also drastically affected by the K-T extinction.
This option is simply, “Choose one from column A, one from column B, one from column C,” until sufficient conditions are reached for the observed data.
But a sufficient condition is a sufficient condition, and the incredible chain of events brought about by the Chicxulub impact would have been a more-than-sufficient condition.
Some recent research indicates that there were, in fact, two back-to-back major extinctions that occurred in this timeframe, one associated with the impact, the other with volcanism (likely the Deccan Traps). The eruption apparently occurred first, and the impact would have finished the matter.
Other Extinction Events
EventTimeframePossible Cause(s)Ordovician-Silurian extinction events (2, back to back)450-440MY Before Present (BP)Global cooling/sea level drop; Possible gamma-ray burstLate Devonian extinction375-360MY BPViluy TrapsPermian-Triassic extinction event aka “The Great Dying”252MY BPSiberian Traps; Wilkes Land impactor; Anoxic eventTriassic-Jurassic extinction event201.3MY BPCentral Atlantic Magmatic Province (CAMP) eruption/breakup of Pangaea; possible impactorCretaceous-Paleogene extinction event66MY BPChicxulub impactor; Deccan Traps
These are only the major extinction events found in the geologic record. More than two dozen can be found or inferred from the fossil record. At least five invoke possible impactor triggers; two invoke other cosmic events, such as a gamma-ray burst or a supernova; nine also invoke various supervolcanic events. Some of these overlap as competing proposed causes.
For more details, check out INCOMING! The Chicxulub Impactor by Stephanie Osborn on Kindle and Nook. [Note, by buying with the link below you’re giving the blog owner a small percentage of the purchase price.]
Dr. Megan McAllister was already a pretty unusual human — NASA astronaut, professional astronomer, polymath — when she encountered the man in the black suit that night in west Texas. What Division One Agent Echo didn’t know, when he recruited her to the Agency, was that she was even more special.
But he’d find out, soon enough.