And despite a thorough search, no increased
levels of iridium have been associated with that
time. So researchers have been looking for other
evidence of an impact.
And now they seem to have found it. The new
study, announced today, uncovered extraterrestrial
gases trapped inside special molecules, known as
Buckyballs, in ancient soil layers. Scientists say
the evidence points to a colossal whack from a
comet or asteroid roughly 3.7 to 7.5 miles (6 to
12 kilometers) wide -- about the same size as the
one that ultimately destroyed most dinosaurs 186
million years later.
"These two extinctions are like bookends for
the age of the dinosaurs," said Robert Poreda, a
University of Rochester scientist who worked on
the study. Full results are in the Feb. 23 issue
of the journal Science.
Rise of intelligent civilization(s)
In the past 500 million years, there have been
about five giant extinction events, researchers
say. The new finding means that at least two of
them were caused by impacts. The others also may
"This suggests that the evolution of life on
Earth is strongly coupled with our cosmic
environment," said Christopher Chyba, a SETI
Institute researcher who was not directly involved
in the study. The new work even has implications
for the origin of intelligence on Earth, and
possibly elsewhere, Chyba said. It hints at the
possibility that Earth's biosphere is regularly
disrupted, every 100 million years or so, by giant
impacts that would render human life impossible.
"We ourselves would truly not have been here
[if not for] the extinction that eliminated the
dinosaurs," Chyba said at a news conference at
NASA Headquarters. "A biosphere only has a certain
amount of time to develop a technical intelligence
which is capable of realizing that there is an
impact hazard, cataloging that hazard
and...avoiding the next impact."
Bottom line: Only a civilization smart enough
to spot the hazard and mitigate it can
Chyba said that because other planets around
other stars would likely face the same risks, the
next logical thought is that any potential
intelligent ET would also have to be quick-witted
to avoid going the way of the dinosaurs. He said
this might "increase the likelihood of technical
"Not a pretty picture for life"
Because Earth's crust has stretched and folded
so dramatically in the past 251 million years, the
researchers say there is no way to pinpoint where
the space rock hit. But they can guess at the wild
events that followed.
Earthquakes and volcanoes would have rattled
the planet, explains the University of
Washington's Luann Becker, lead author of a study.
Lava poured out in volume -- enough to cover the
planet 10 feet (3 meters) deep. The oceans dropped
820 feet (250 meters).
Worse, the combined effects of the object
vaporizing on impact, along with all the
volcanism, poisoned what was left of the seas and
choked the air with ash and deadly gases. Sunlight
may have disappeared for months. Or, Becker and
her colleagues say, carbon dioxide may have
trapped the Sun's energy and sent temperatures
Either way, it was "not a pretty picture for
life, which is why it's the greatest of all mass
extinctions recorded on Earth," Becker told
Some 90 percent of all sea life perished, along
with 70 percent of land animals and most
The researchers say the volcanic activity was
likely going on before the impact, but was then
fueled into a frenzy. The one-two punch, it seems,
may be what's needed to precipitate the worst
extinctions. Poreda called the whole scenario a
"blast from the double-barreled shotgun."
The discovery, and the new technique used to
make it, could lead scientists to find that some
of the other 20 or so mass extinctions in the last
billion years were also caused, or at least helped
along, by cosmic collisions.
Next page: ET Buckyballs left as a calling