Dinosaur-killing asteroid impact fouled Earth's atmosphere with dust
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[October 31, 2023]
By Will Dunham
WASHINGTON (Reuters) - It was, to put it mildly, a bad day on Earth when
an asteroid smacked Mexico's Yucatan Peninsula 66 million years ago,
causing a global calamity that erased three-quarters of the world's
species and ended the age of dinosaurs.
The immediate effects included wildfires, quakes, a massive shockwave in
the air and huge standing waves in the seas. But the coup de grâce for
many species may have been the climate catastrophe that unfolded in the
following years as the skies were darkened by clouds of debris and
temperatures plunged.
Researchers on Monday revealed the potent role that dust from pulverized
rock ejected into the atmosphere from the impact site may have played in
driving extinctions, choking the atmosphere and blocking plants from
harnessing sunlight for life-sustaining energy in a process called
photosynthesis.
The total amount of dust, they calculated, was about 2,000 gigatonnes -
exceeding 11 times the weight of Mt. Everest.
The researchers ran paleoclimate simulations based on sediment unearthed
at a North Dakota paleontological site called Tanis that preserved
evidence of the post-impact conditions, including the prodigious dust
fallout.
The simulations showed this fine-grained dust could have blocked
photosynthesis for up to two years by rendering the atmosphere opaque to
sunlight and remained in the atmosphere for 15 years, said planetary
scientist Cem Berk Senel of the Royal Observatory of Belgium and Vrije
Universiteit Brussel, lead author of the study published in the journal
Nature Geoscience.
While prior research highlighted two other factors - sulfur released
after the impact and soot from the wildfires - this study indicated dust
played a larger role than previously known.
The dust - silicate particles measuring about 0.8-8.0 micrometers - that
formed a global cloud layer were spawned from the granite and gneiss
rock pulverized in the violent impact that gouged the Yucatan's
Chicxulub (pronounced CHIK-shu-loob) crater, 112 miles (180 km) wide and
12 miles (20 km) deep.
In the aftermath, Earth experienced a drop in surface temperatures of
about 27 degrees Fahrenheit (15 degrees Celsius).
"It was cold and dark for years," Vrije Universiteit Brussel planetary
scientist and study co-author Philippe Claeys said.
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This illustration depicts paleoclimate model simulations that show
the rapid dust transport across Earth, indicating that the world was
encircled by the silicate dust ejecta within a few days following
the impact of an asteroid off Mexico's coast 66 million years ago in
this undated handout. Cem Berk Senel/Handout via REUTERS
Earth descended into an "impact winter," with global temperatures
plummeting and primary productivity - the process land and aquatic
plants and other organisms use to make food from inorganic sources -
collapsing, causing a chain reaction of extinctions. As plants died,
herbivores starved. Carnivores were left without prey and perished.
In marine realms, the demise of tiny phytoplankton caused food webs
to crash.
"While the sulfur stayed about eight to nine years, soot and
silicate dust resided in the atmosphere for about 15 years after the
impact. The complete recovery from the impact winter took even
longer, with pre-impact temperature conditions returning only after
about 20 years," Royal Observatory of Belgium planetary scientist
and study co-author Özgür Karatekin said.
The asteroid, estimated at 6-9 miles (10-15 km) wide, brought a
cataclysmic end to the Cretaceous Period.
The dinosaurs, aside from their bird descendants, were lost, as were
the marine reptiles that dominated the seas and many other groups.
The big beneficiary were the mammals, who until then were bit
players in the drama of life but were given the opportunity to
become the main characters.
"Biotic groups that were not adapted to survive dark, cold and
food-deprived conditions for almost two years would have experienced
massive extinctions," Karatekin said. "Fauna and flora that could
enter a dormant phase - for example, through seeds, cysts or
hibernation in burrows - and were able to adapt to a generalistic
lifestyle - not dependent on one particular food source - generally
survived better, like small mammals."
Absent this disaster, dinosaurs might still dominate today.
"Dinos dominated Earth and were doing just fine when the meteorite
hit," Claeys said. "Without the impact, my guess is that mammals -
including us - had little chance to become the dominant organisms on
this planet."
(Reporting by Will Dunham, Editing by Rosalba O'Brien)
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