"It sounds like a headline from a supermarket tabloid, but the
idea may not be as outlandish as it first appears. One hundred tons
(90 metric tons) of space debris fall on Earth every day; some
scientists believe as much as one ton (0.9 metric ton) of bacteria
from space is part of that daily deposit.
Particles carrying the SARS virus could have come from a comet, the
researchers say, and released into the debris trail of the comet's
tail. The Earth's passage through the stream would have led to the
entry of the culprit particles.
"We're not saying this is definitely what happened," said
Wickramasinghe, who is also the director of the Cardiff Centre for
Astrobiology, a research effort that seeks evidence of
extraterrestrial life. "But the theory should not be ruled
out."
SARS, or severe acute respiratory syndrome, has so far infected at
least 8,384 people and claimed 770 lives. Mainland China, Hong
Kong, Taiwan, and Canada have been hit hardest by the
epidemic.
Independent Evolution
Although SARS has been identified as a coronavirus, the virus is
unexpectedly novel. An independent evolution of the virus may have
been required, which, Wickramasinghe says, adds credibility to his
argument that SARS has an external origin.
According to his theory, a small amount of the virus introduced
into the stratosphere could have lead to an initial fallout east of
the Himalayas, where the stratosphere is thinnest, followed by
sporadic deposits in neighboring areas.
"There would be a first point of descent," said Wickramasinghe.
"This could have been in China."
But most medical experts are sticking to a more conventional
explanation for the origin of SARS.
"We have no scientific evidence that SARS or any other infectious
disease has dropped off a meteor at this point in time," Julie
Gerberding, director of the Atlanta-based Centers for Disease
Control and Prevention, said at a recent briefing. "Should we
discover any evidence supportive of that, we would let you
know.
Gerberding said SARS is most explainable by natural evolution of
coronaviruses, either from an animal or a poultry source, or
possibly a coronavirus that's evolved in a human. "We have many
hypotheses that are far more plausible than meteorites," she
said.
Collecting Bacteria
About 100 tons (90 metric tons) of comet debris reach the Earth on
a daily basis, and Wickramasinghe says there is evidence for life
arriving with this debris.
In an experiment two years ago, he and scientists from the
Bangalore-based Indian Space Research Organization sent sterile
collecting devices into space and brought back large quantities of
microorganisms in samples of stratospheric air captured at an
altitude of 26 miles (41 kilometers). The researchers were able to
culture, or grow, two types of microorganisms, which proved similar
to known terrestrial species.
"Our findings lend support to the view that microbial material
falling from space is, in a Darwinian sense, highly evolved, with
an evolutionary history closely related to life that exists on
Earth," said Wickramasinghe.
He estimates that a ton (0.9 metric ton) of bacterial material
falls onto Earth every day, translating into more than 1,000 types
of bacteria. Most of this material simply adds to the unculturable
or uncultured microbial flora present on Earth.
The researchers argue that the random nature of epidemics adds
credence to their argument that disease-causing bacteria and
viruses may be evolving in outer space, parallel to those on
Earth.
"New epidemics have a record of abrupt entrances from time to
time," said Wickramasinghe. "The patterns of spread of these
diseases are difficult to explain simply on the basic of endemic
infective agents."
He says the unusual nature of major epidemics, such as the
influenza epidemic of 1917-19, where infection rates were not
easily explained by epidemiological modeling, bears the hallmarks
of a space incident.
"Although person-to-person spread occurred in local areas, the
disease appeared on the same day in widely separated parts of the
world on the one hand, but, on the other, took days to weeks to
spread relatively short distances," said Wickramasinghe.
The Origins of Life on Earth
The idea that SARS may have originated from space is based on the
argument that life first appeared on Earth some four billion years
ago when the Earth suffered a prolonged period of comet
impacts.
This is a controversial theory. Most scientists believe that life
on Earth began as a "primordial soup" in a lake or pond some 3.5
billion years ago: Chemicals from the atmosphere combined with some
form of energy necessary to make amino acids (the building blocks
of proteins) to create the first primitive organisms, kicking off
the evolution of all species on Earth.
Wickramasinghe disagrees. He believes life did not start on Earth,
but evolved on a much bigger scale, in a cluster of galaxies. Earth
merely became an "assembly station" for all the cosmic genes.
"If Earth evolved in a closed-box situation, the argument we're
making about SARS would not carry much weight," he said. "But if
you accept the argument that life on Earth started from the
outside, then all viruses originated from the outside."