[meteorite-list] Mammoths Found Peppered with Meteorite Fragments

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 12 Dec 2007 11:23:33 -0800 (PST)
Message-ID: <200712121923.LAA24638_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/2/hi/science/nature/7130014.stm

Great beasts peppered from space
By Jonathan Amos
BBC News
December 11, 2007

Startling evidence has been found which shows mammoth and other great
beasts from the last ice age were blasted with material that came from
space.

Eight tusks dating to some 35,000 years ago all show signs of having
being peppered with meteorite fragments.

The ancient remains come from Alaska, but researchers also have a
Siberian bison skull with the same pockmarks.

The scientists released details of the discovery at a meeting of the
American Geophysical Union in San Francisco, US.

They painted a picture of a calamitous event over North America that may
have severely knocked back the populations of some species.

Blast direction

"We think that there was probably an impact which exploded in the air
that sent these particles flying into the animals," said Richard
Firestone from the Lawrence Berkeley National Laboratory.

"In the case of the bison, we know that it survived the impact because
there's new bone growth around these marks."

And geoscience consultant Allen West added: "If the particles had gone
through the skin, they may not have made it through to vital organs; but
this material could certainly have blinded the animals and severely
injured them."

The mammoth and bison remains all display small (about 2-3mm in size)
perforations.

Raised, burnt surface rings trace the point of entry of high-velocity
projectiles; and the punctures are on only one side, consistent with a
blast coming from a single direction.

Viewed under an electron microscope, the embedded fragments appear to
have exploded inside the tusk and bone, say the researchers. Shards have
cut little channels.

The sunken pieces are also magnetic, and tests show them to have a high
iron-nickel content, but to be depleted in titanium.

The ratios of different types of atoms in the fragments meant it was
most unlikely they had originated on Earth, the team told the AGU meeting.

Magnetic hunt

The discovery follows on from the group's previous research which
claimed a more recent space collision - some 13,000 years ago.

The researchers reported the discovery of sediment at more than 20 sites
across North America that contained exotic materials: tiny spheres of
glass and carbon, ultra-small specks of diamond and amounts of the rare
element iridium that were too high to be terrestrial.

The scientists also found a black layer which, they argued, was the
charcoal deposited by wildfires that swept the continent after the space
object smashed into the Earth's atmosphere.

It was just a tiny magnet on a string, but very strong. It would swing
over and stick firmly to these little dots
Allen West

"We had found evidence of particle impacts in chert, or flint, at a
Clovis Indian site in Michigan," Dr Firestone said.

"So, we got the idea that if these impacts were in the chert, then they
might likely also have occurred in large surfaces such as tusks; and we
decided it was worth a shot to go look for them."

Allen West began the hunt at a mammoth tusk sale in his home state of
Arizona.

He immediately found one tusk with the tell-tale pockmarks and asked the
trading company if he could look through its entire collection. He
sorted literally thousands of items.

"There are many things that can cause spots, such as algae, and there
were a few of those; but I was only interested in the ones that were
magnetic," he recalled. "It was just a tiny magnet on a string, but very
strong. It would swing over and stick firmly to these little dots."

The search turned up a further seven ivory specimens of interest,
together with the bison skull.

Further clues

But having gone out and tested the hypothesis of tusk impacts, and
having apparently uncovered such items - the team was then astonished to
find the animal remains were about 20,000 years older than had been
anticipated.

The researchers are now considering a number of possibilities - one that
could even tie the older remains to the younger event.

"People who collect these items today in Siberia and Alaska frequently
find the tusks sticking out of the permafrost or eroding out of a
riverbank," explained Mr West.

"Maybe, these were tusks from dead animals that were just exposed on the
surface, so when this thing blew up in the atmosphere, it would have
peppered them. The date could really be anywhere from 13,000 to
35-40,000 years ago."

The team believes there must still be peppered tusks out there that can
be dated to 13,000 years ago, and the hope is that the AGU presentation
will prompt museums and collectors to look through their archives.

"There should also be a layer of this same meteoritic material in the
sedimentary record. It's probably very thin. If we can locate the right
place and it hasn't been turbated, we should be able to find this layer;
and it shouldn't be too different from the impact layer we found for the
13,000-year event," said Dr Firestone.

Neither proposed impact can yet be tied definitively to any craters - if
there ever were any. The team also needs to explain how the bison and
mammoth remains can show similar damage when they were widely separated
geographically.

Past puzzle

The intriguing question is how space impacts might fit into the
extinction story of the ice age beasts. The mammoth, their elephant
cousins the mastodon, sabre-toothed tigers, some bears, and many other
creatures all disappeared rapidly from the palaeo-record about 10,000
years ago.

Their loss has traditionally been put down to either climate change
and/or the efficient hunting technologies adopted by migrating humans.

Could impacts have also weakened these populations?

It might be just one more element to factor into what is a really
complex picture, commented Dr Ian Barnes from Royal Holloway University
of London, UK.

The British researcher studies the DNA of ancient animals to try to
glean details of how their populations changed over time.

He said there were some interesting markers in the genetics of different
creatures some 30,000 to 45,000 years ago - but it was extremely hard to
draw firm conclusions.

"For us the difficulty is that we see patterns but we don't understand
what the underlying process is; so it becomes difficult to ascribe
causation," he explained.

"Just as in a modern crime scene, it's very difficult to piece all the
evidence together and say precisely what was going on; which event led
to any particular outcome."

But he added: "Certainly, you can't imagine it helped the animals having
a large meteorite hit the Earth's atmosphere and pellet them with shot."
Received on Wed 12 Dec 2007 02:23:33 PM PST