One of the biggest cosmic dust
storms of the past 80 million years left a blanket of material on Earth after
an asteroid in space broke apart, researchers said today.
The conclusion is based on evidence
in ocean sediments, which computer models have tied to an observed bevy of
asteroid siblings still roaming the solar system.
The thinking is that the space rocks
were once part of a larger asteroid, some 100 miles (160 kilometers) wide, that
broke up - possibly in a collision
- out in the asteroid belt between Mars and Jupiter. The drama took place
8.2 million years ago. That much has been reasoned before. The event would have
created vast amounts of dust, some of which would have been scooped up
by our planet.
In the Jan. 19 issue of the journal Nature,
scientists report a spike in helium 3,
a type of helium that's rare on Earth and typically of extraterrestrial origin,
in a layer of sediment dated to that time frame.
The dust rich in helium 3 spiked
about 8.2 million years ago and gradually decreased over the course of 1.5
million years, the data shows.
"The helium 3 spike found in
these sediments is the smoking gun that something quite dramatic happened to
the interplanetary dust population 8.2 million years ago," said Caltech
geochemist Ken Farley. "It's one of the biggest dust events of the
last 80 million years."
Interplanetary dust is nothing new
to scientists. About 20,000 tons of it lands on Earth every year. While in
space, it picks up helium 3 from a wind of material flowing out from the Sun.
When asteroids collide, more debris
wafts through the solar system. Much of it is drawn toward the Sun, and on its
way in some is captured by Earth.
The particles are small and rare,
making up much less than less than one part per million of terrestrial
sediments, so the new discovery was no easy task. Farley and his colleagues
studied sediment from beneath the Indian Ocean and the Atlantic, showing that
the same event was recorded at two widely separated locations.
The long-gone large asteroid has
been previously dubbed Veritas. It is survived by
fragments that roam in orbits researchers have traced back to a common origin.
"While asteroids are constantly
crashing into one another in the main asteroid belt," said study member
William Bottke of the Southwest Research Institute,
"only once in a great while does an extremely large one shatter."
Computer simulations show the Veritas event could have produced the sudden spike in dust
and the gradual decline in accumulation.
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