Chicxulub Stirred the Microbial Biosphere

The Chicxulub impactor killed off most of the dinosaurs and a lot of the life on Earth.  And the effects lasted thousands, even hundreds of thousands of years. It was a bad day to be a living thing on Earth, that’s for sure.

But even a megaevent like Chicxulub didn’t wipe out all life.  In the recovery, microbes flourished, plants and forests spread, and birds took over the skies.

This summer there are several more studies showing how the impact stirred the pot and led to the spread of various lifeforms.

In addition to forests and birds (and frogs) (and, of course mammals), the Chicxulub impact was followed by a radiation of snakes [4]. The researchers speculate that snakes may have survived in fresh water aquatic habitats, and adaptation for night hunting might have been an advantage in the dim years of the aftermath.  Then, of course, snake, like birds and frogs, invaded the new forests that arose.

But wait!  There’s more!

The Chicxulub impact dug a huge hole and shattered rocks a kilometer and more into the crust.  Researchers from the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 report an analysis of the microbial life found in the core drilled from the impact crater [2]. 

The shattered rock created a range of microscopic habitats, which persist even today.  As their title says, in addition to blasting surface life, the impact “continues to shape the deep subsurface biosphere at Chicxulub in the present day.”  ([2], p. 1)

Another study found that the impactor infused the crater with sulfate-rich minerals, and when water rushed into the hole, created hot, sulfur rich conditions [5].  This was likely quickly occupied by thermophilic sulfate-reducing organisms, which still exist deep in the rocks.

“Thermophilic sulfate-reducing organisms that currently occur in the same rocks, now buried hundreds of meters beneath the seafloor, may be the living remnants of that ∼66 to 63 million-year-old colony of microorganisms.”

([5], p. 110)

The researchers note that the Chicxulub object likely was similar to many other impactors on Earth and throughout the solar system.  This suggests that the long history of bombardment will have influenced the evolution of the deep biosphere, which exists today.  Deep in the rocks, life is descended from collisions with space debris!

The researchers also note that these findings suggest that the history of life here and anywhere else would be strongly affected by this kind of repeated astronomical “tilling” of rocky planetary crusts.

Cool!

We puny humans like to talk about how the death of the dinosaurs made way for us.  But it is increasingly clear that Chicxulub basically reset and reshuffled all life on Earth, and the results can still be seen today.

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1. Helen Briggs, Asteroid that wiped out dinosaurs shaped fortunes of snakes, in BBC News – Science & Environment, September 14, 2021. https://www.bbc.com/news/science-environment-58559735
2. Charles S. Cockell, Bettina Schaefer, Cornelia Wuchter, Marco J. L. Coolen, Kliti Grice, Luzie Schnieders, Joanna V. Morgan, Sean P. S. Gulick, Axel Wittmann, Johanna Lofi, Gail L. Christeson, David A. Kring, Michael T. Whalen, Timothy J. Bralower, Gordon R. Osinski, Philippe Claeys, Pim Kaskes, Sietze J. de Graaff, Thomas Déhais, Steven Goderis, Natali Hernandez Becerra, Sophie Nixon, and Iodp-Icdp Expedition Scientists, Shaping of the Present-Day Deep Biosphere at Chicxulub by the Impact Catastrophe That Ended the Cretaceous. Frontiers in Microbiology, 12:1413,  2021. https://www.frontiersin.org/article/10.3389/fmicb.2021.668240
3. Becky Ferreira, The Rock That Ended the Dinosaurs Was Much More Than a Dino Killer, in tNew York imes. 2021: New York. https://www.nytimes.com/2021/09/13/science/chicxulub-dinosaur-extinction.html
4. Catherine G. Klein, Davide Pisani, Daniel J. Field, Rebecca Lakin, Matthew A. Wills, and Nicholas R. Longrich, Evolution and dispersal of snakes across the Cretaceous-Paleogene mass extinction. Nature Communications, 12 (1):5335, 2021/09/14 2021. https://doi.org/10.1038/s41467-021-25136-y
5. David A. Kring, Martin J. Whitehouse, and Martin Schmieder, Microbial Sulfur Isotope Fractionation in the Chicxulub Hydrothermal System. Astrobiology, 21 (1):103-114, 2021/01/01 2020. https://doi.org/10.1089/ast.2020.2286

Extinction is an Opportunity

One of the problems with the history of mass extinctions is the definition of the very concept itself.  It’s easy enough to define something like the extinction of the Dodo, where we have a distinctive animal, and we know the population went down to zero.  On the other hand, Homo neaderthalis is “extinct”—except some of the genes persist in the genome of Home sapiens.  So, the phenotypes aren’t seen, but the genome still exists, at least in part.

And then there is the episodes of “mass” extinction, when a lot of species die out at the same time.  We have evidence of five such catastrophes in the history of the Earth, and we are working hard to implement a sixth extinction. The problem is, these events are known from the fossil record, which is hardly complete.

So, yeah, a lot of big dinosaurs died out after the Chicxulub impact.  So did other species, including plants and other animals.  There is evidence that a lot of the coral and plankton died out, too.  Of course, other species survived, including the ancestors of mammals and avian dinosaurs.

But we really don’t have much information about things that don’t leave fossils.  How did fungus fair?  Insects?  Microbes in general?  What about cave dwellers?  Extremophiles that live deep underground?  Tubeworms living at ocean vents?  These species wouldn’t necessarily be as vulnerable to the impact and ensuing nuclear winter.

When we read about “most life being wiped out”, is this really accurate?  Or do we mean, “life that is similar to us”?  And if many species are wiped out, others may be advantaged.  A “mass extinction” is certainly a big event, but to some extent it is may be a “decapitation”, wiping out dominant species, and paving the way for others.

This month researchers report further examination of the drill cores collected by the IODP from the Chicxulub crater [2].  The new study focused on what happened after impact, as the surviving life recovered.  The focus of this study are traces of organic molecules, which are markers for bacteria, including cyanobacteria.

And the results are…interesting.

First of all, not everything died. Second, life came roaring back, right away!

There is a clear layer of debris that was likely left by tsunamis and by water returning into the really big hole.  But above that level, there is evidence of cyanobacteria, blue green algae which characteristic live in low oxygen conditions.  So, in this reeking still hot crater, under soot blotted skies, highly acidic water leaked in—and the cyanobacteria were on it!

At first, there was only a little pond scum, struggling in the dark.  But within a couple of hundred thousand years it looks like there were a lot of algae mats, growing great guns.  And there were layers of oxygenated water, too.  With other species thriving on the abundant nutrients washed down from the devastated continents.

“The nascent Chicxulub crater basin was accompanied by major transitions in nutrient and oxygen supplies (periods of euxinia) that shaped the recovery of microbial life.”   ([2], p.4)

OK, the cool dinosaurs were gone, and the lovely exotic plant scape was charcoal.  And the reefs and fishes were dead, too.

But there was plenty of life.  And, by gum, with all those showboat dinosaurs out of the way, there was space to grow!

Which goes to show that it takes more than a mere planet-cracking impact to wipe out “all life” on Earth.

On the other hand, the top species were definitely bumped off, drowned, burnt, smothered and starved.  It took hundreds of thousands, and millions of years for things to recover to a similar state (i.e., lots of big, cool looking animals and fish).

So, yeah, the Anthropocene extinction probably won’t wipe out all life.  But it will surely do us to death, and it may take hundreds of thousands of years to recover from the massive impact of the human explosion.

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1. Shannon Hall, Asteroid That Killed the Dinosaurs Was Great for Bacteria, in New York Times. 2020: New York. https://www.nytimes.com/2020/02/01/science/asteroid-dinosaurs-crater-bacteria.html
2. Bettina Schaefer, Kliti Grice, Marco J. L. Coolen, Roger E. Summons, Xingqian Cui, Thorsten Bauersachs, Lorenz Schwark, Michael E. Böttcher, Timothy J. Bralower, Shelby L. Lyons, Katherine H. Freeman, Charles S. Cockell, Sean P. S. Gulick, Joanna V. Morgan, Michael T. Whalen, Christopher M. Lowery, and Vivi Vajda, Microbial life in the nascent Chicxulub crater. Geology, 2020. https://doi.org/10.1130/G46799.1

 

A Chicxulub Core

It seems obvious, so I wonder why no one has done it before.  We should drill more cores in the Chicxulub crater to get detailed records of the event.

This fall the international International Ocean Discovery Program (IODP)–International Continental Scientific Drilling Program (ICDP) Expedition 364 team reports on a new core drilled into the rim of the Chicxulub crater in 2016, documenting, as the title puts it, “The first day of the Cenozoic” [2].  The new site was on the peak ring of the crater, aimed to get a long, undisturbed record of the event.

The outer rim (white arc) of the crater lies under the Yucatan Peninsula Image credit: NASA

It was a helluva thud, blowing open a 50km crater, 25km into the crust, vaporizing gigtons of Carbon and, evidently, Sulfur, from the rocks in the first minute.    A few minutes later, the crust rang back, with melted rock flowing out.  Within 30 minutes, the displaced water returned, initiating exciting explosions as cool water met molten rock.  The impact created monster tsunamis, which rebounded and returned to the crater later in the day.

Fig. 2. Key events within the first day of the Cenozoic based on numerical modeling, geophysical data, and IODP Expedition 364 drilling. The figure includes 2 perspectives: a westerly oriented radial profile crossing inner crater rim and shallow shelf and a northeasterly oriented radial profile that crosses the opening in crater rim into the Gulf of Mexico. (A) Approaching 12-km-sized impactor over the preimpact target of the Yucatán peninsula. (B) A 100-km-wide transient crater and remnant of the impact plume consisting of vaporized/fragmented limestones, evaporites, and granitic basement rocks (timescale and geometry based on ref. 5). (C) Collapse of the transient crater with upward formation of a central uplift starting to undergo dynamic collapse (timescale and geometry based on refs. 5, 9, and 44). (D) Morphology after central uplift collapse and peak ring formation (based on refs. 2 and 9). Initial ocean resurge is depicted entering the crater with timescale based on a dam break model and undergoing MWIs. (E) Ocean resurge completes cresting the peak ring where Site M0077 was drilled. (F) Settling of debris within the now flooded crater to form the bulk of the suevite deposit that blankets the peak ring, with a zoomed-in view of processes (including seiches) and deposits capping the peak ring. (G) Tsunami entering crater from returning rim-wave tsunami and shelf collapses, with a zoomed-in view of the peak ring K-Pg deposits (timescale based on ref. 34). Rx, rocks. (From [2])

Besides the massive earthquakes, tsunamis, and fires which raged for months, the event ejected huge amounts of Sulfur, and a variety of particulates, which surely blotted out the sun and probably triggered a “nuclear winter” for years.

It was a bad day to be a dinosaur.

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1. Jonathan Amos, The day the dinosaurs’ world fell apart, in BBC News – Science & Environment. 2019. https://www.bbc.com/news/science-environment-49651406
2. Sean P. S. Gulick, Timothy J. Bralower, Jens Ormö, Brendon Hall, Kliti Grice, Bettina Schaefer, Shelby Lyons, Katherine H. Freeman, Joanna V. Morgan, Natalia Artemieva, Pim Kaskes, Sietze J. de Graaff, Michael T. Whalen, Gareth S. Collins, Sonia M. Tikoo, Christina Verhagen, Gail L. Christeson, Philippe Claeys, Marco J. L. Coolen, Steven Goderis, Kazuhisa Goto, Richard A. F. Grieve, Naoma McCall, Gordon R. Osinski, Auriol S. P. Rae, Ulrich Riller, Jan Smit, Vivi Vajda, and Axel Wittmann, The first day of the Cenozoic. Proceedings of the National Academy of Sciences:201909479, 2019. http://www.pnas.org/content/early/2019/09/04/1909479116.abstract