[meteorite-list] How Organisms Survived Asteroid Impacts

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 10 Sep 2009 17:22:48 -0500
Message-ID: <CD9681937D334A46AB41C044B0993875_at_ATARIENGINE2>

http://www.space.com/scienceastronomy/090910-am-impact-mixotrophs.html

Life in the Dark: How Organisms Survived Asteroid Impacts
By Jeremy Hsu -- Astrobiology Magazine
10 September 2009

A dinosaur-killing asteroid may have wiped out
much of life on Earth 65 million years ago, but
now scientists have discovered how smaller
organisms might have survived in the darkness
following such a catastrophic impact.

Survival may have depended upon jack-of-all-trades
organisms called mixotrophs that can consume
organic matter in the absence of sunlight. That
would have proved crucial during the long months
of dust and debris blotting out the sun, when plenty
of dead or dying organic matter filled the Earth's
oceans and lakes.

"Mixotrophs are very good at stabilizing situations
by using whatever resources are there, and can
often provide what resources there aren't," said
Harriet Jones, a biologist at the University of
East Anglia in the UK. "They're very good at
coping in extreme environments, and enabling
other organisms to live."

Jones and her colleagues tested the limits of
mixotrophs by subjecting them to six months
of low light or complete darkness. The mixotrophs
not only thrived, but also surprised researchers
by helping sunlight-dependent organisms also
survive pitch black conditions.

Scientists have long debated the overall impact
of the K-T extinction that may have heralded the
end of the dinosaurs, but most researchers agree
that such an event would have thrown up enough
dust and debris to darken Earth's skies for about
six months. A lack of sunlight would have killed
off a majority of plants, eliminating the food supply
for animals higher up the food chain.

Many scientists assumed that even smaller organisms
would struggle just to stay alive during months of
almost complete darkness. Some previous studies
even looked at how some organisms such as
mixotrophs can survive low light and low food
conditions. But no one had tried to test how well
mixotrophs would survive the catastrophic
environment following something such as the
K-T event, Jones said.

"The literature was always saying in that biological
production would cease in a post-catastrophic
environment," Jones noted. "We felt that because
of what mixotrophy algae could do, that wasn't
always the case."

Jones joined forces with Charles Cockell, a
microbiologist at the Open University based in
the UK who specializes in catastrophic environments,
as well as other researchers. They tested both
freshwater and ocean mixotrophs under conditions
ranging from low light to complete darkness for
six months, and added food sources during
short-term experiments to simulate decaying
organic matter.

However, Jones and her colleagues also wanted
to see how mixotrophs fared when living together
with phototrophs, or light-dependent organisms.
They tested mixotrophs and phototrophs separately
and together under the different light conditions.

Turns out that the mixotrophs survived all the
experiments, and some even grew under the low
light conditions. Their ability to consume other
organisms or organic matter helped them rebound
quickly after low light returned, perhaps similar
to the clouds of dust and debris finally beginning
to clear.

But the real shock came from how well light-dependent
organisms did when living with the mixotrophs. No
photosynthesis could take place under the complete
darkness, but the phototrophs mostly managed to
survive based on nutrients cycled by the active
mixotrophs.

"We were extremely surprised at how well phototrophs
did during six months darkness, when they can't
eat at all," Jones said. Such findings may cause
researchers to rethink how well certain life forms
survived the catastrophic impacts that dot Earth's
geological record.

Furthermore, the mixotroph activity allowed the
phototroph populations to rebound quickly back
to normal within a month. And in the end, both
mixotrophs and phototrophs tended to fare better
when living together.

"So long as mixotrophs are cycling nutrients,
[phototroph] algae can take off quickly and get
the life cycle going," Jones explained.

Only one low light condition saw phototrophs
fail to survive while living with mixotrophs. The
phototrophs may have used too much energy
trying to do photosynthesis in the weak light,
or perhaps the hungry mixotrophs simply fed
on their fellow organisms.

"You can only do so much in a flask, and obviously
the mix of species would be much greater in a
natural environment," Jones pointed out.

Still, the overall results suggest how mixotrophs
provide a cushion against catastrophe for certain
ecosystems, and may even prevent huge population
crashes. The research is further detailed in the
July/August issue of the journal Astrobiology.

Jones and her colleagues plan to conduct more
studies with greater mixes of species, in an
environment that would more closely resemble
the natural world. They also want to shorten
experiments to three months rather than six.

That looks all well and good for the smaller organisms.
But humans, who would have a much harder time
feeding themselves if the skies went dark, may want
to plan on how to prevent such catastrophic asteroid
impacts in the future
Received on Thu 10 Sep 2009 06:22:48 PM PDT