- WASHINGTON (Reuters) - Space dust from broken-up asteroids may have started
the dinosaurs down the road to gradual extinction, astronomers said Thursday.
The final blow probably came when larger pieces of the asteroids actually
collided with the Earth, the researchers at the University of Florida and
the Carnegie Institution of Washington said. The good news, according to
the report in the journal Science, is that Earth would have about a million
years warning before another such asteroid impact.
- Stephen Kortenkamp, a planetary scientist
at the Carnegie Institution who co-wrote the report, said astronomers have
known about this space dust for some time. He and Stanley Dermott at the
University of Florida ran computer models based on a collection of observations
on Earth and in space. ``You would have an asteroid that would have been
in a collision. The type of asteroid is called a rubble-pile asteroid,''
Kortenkamp said in a telephone interview.
- ``It's just a collection of debris that
ranges in size from dust particles to two-km (one-mile) sized bodies.''
The dust strings out, and such scatterings of dust have been seen strung
between the asteroid belt and the Earth, Kortenkamp said.
- It comes from three ``families'' of asteroids
-- agglomerations of rocks and dust that were once a single asteroid. The
asteroid belt lies between Mars and Jupiter. The dust, being lighter than
the larger bits, is more easily influenced by the Sun's rays. It ``falls''
in toward the Sun much faster than the larger pieces, gradually spiraling
in as it orbits.
- The Earth passes through this dust cloud
as it orbits, too. ``The dust gets here first and any impacters that come,
come later,'' Kortenkamp said. Kortenkamp and Dermott, who looked at other
researchers' studies of space dust taken from sea floor sediments, said
they found the dust accumulates on a 100,000-year cycle. ``There are two
different mechanisms -- one delivers the dust and another delivers the
asteroids, dust first, and the fragments a million years later,'' Kortenkamp
said. There was evidence for this in the geological record, Kortenkamp
- This could explain why the dinosaurs
appear to have been gradually becoming extinct before the asteroid collision
that is believed to have caused the big extinction 65 million years ago.
Currently, about 30,000 metric tons of dust from these asteroids falls
to the Earth every year, but in the past the rate has been as much as 10
million tons a year. ``That is comparable to what we know is injected into
the atmosphere by a large volcano, and we know volcanoes have affected
the climate,'' Kortenkamp said.
- That much matter could cause a ``nuclear
winter'', Kortenkamp said -- a pall of dust that would block out so much
sun that temperatures would fall, the ice caps would grow and much plant
and animal life would die off. None of this has immediate implications
for humanity, but is of great geological interest, Kortenkamp said. ``It's
not like you find one and a week later it's got you,'' he said. ``It's
more looking back in time.'' He said this accretion of dust probably did
not cause the most recent Ice Ages because the timescales are too long,
although it may have caused ice ages millions of years ago.