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Tässä juttu tuosta UV-keväästä.
Jarmo
- Original Message ----- | Oregon State University
|
| SOURCES:
| Andrew Blaustein, 541-737-5356
| Charles Cockell, (international) 44-1223-221560
|
| 03-09-00
|
| Asteroid devastation could even be worse than feared
| By David Stauth, 541-737-0787
|
| CORVALLIS, Ore. -- Researchers say in a new report that if a huge
| asteroid were to hit the Earth, the catastrophic destruction it
| causes, and even the "impact winter" that follows, might only be a
| prelude to a different, but very deadly phase that starts later on.
|
| They're calling it, "ultraviolet spring."
|
| In an analysis of the secondary ecological repercussions of a major
| asteroid impact, scientists from Oregon State University and the
| British Antarctic Survey have outlined some of the residual effects
| of ozone depletion, acid rain and increased levels of harmful
| ultraviolet radiation. The results were just published in the journal
| Ecology Letters.
|
| The findings are frightening. As a number of popular movies have
| illustrated in recent years, a big asteroid or comet impact would in
| fact produce enormous devastation, huge tidal waves, and a global
| dust cloud that would block the sun and choke the planet in icy,
| winter-like conditions for months. Many experts believe such
| conditions existed on Earth following an impact around the
| Cretaceous-Tertiary, or K-T boundary, when there was a massive
| extinction of many animals, including the dinosaurs.
|
| That's pretty bad. But according to Andrew Blaustein, a professor of
| zoology at Oregon State University, there's more to the story.
|
| "Scientists have pretty well documented the immediate destruction of
| an asteroid impact and even the impact winter which its dust cloud
| would create," Blaustein said. "But our study suggests that's just
| the beginning of the ecological disaster, not the end of it."
|
| Blaustein and colleague Charles Cockell examined an asteroid impact
| of a magnitude similar to the one that occurred around the K-T
| boundary, which is believed to have hit off the Yucatan Peninsula
| with a force of almost one trillion megatons.
|
| The immediate results would be catastrophic destruction and an impact
| winter, with widespread death of plants and the large terrestrial
| animals -- including humans -- that most directly depend on those
| plants for food. That's the beginning of an ugly scenario, the
| researchers say.
|
| As a result of the impact, the atmosphere would become loaded with
| nitric oxide, causing massive amounts of acid rain. As they become
| acidified, the lakes and rivers would have reduced amounts of
| dissolved organic carbons, which would allow much greater penetration
| of ultraviolet light.
|
| At first, of course, the ultraviolet rays would be blocked by the
| dust cloud, which sets the stage for a greater disaster later on.
| Many animals depend on some exposure to ultraviolet light to keep
| operational their biological protective mechanisms against it --
| without any such light, those protective mechanisms would be eroded
| or lost.
|
| During the extended winter, animals across the biological spectrum
| would become weaker, starved and more vulnerable. Many would die.
| Then comes ultraviolet spring, shining down on surviving plants and
| animals that have lost their resistance to ultraviolet radiation and
| penetrating more deeply, with greater intensity, into shallow waters
| than it ever has before.
|
| "By our calculations, the dust cloud would shield the Earth from
| ultraviolet light for an extended period, with it taking about 390
| days after impact before enough dust settled that there would be an
| ultraviolet level equal to before the impact. After that, the ozone
| depletion would cause levels of ultraviolet radiation to at least
| double, about 600 days after impact."
|
| According to their study, these factors would lead to
| ultraviolet-related DNA damage about 1,000 times higher than normal,
| and general ultraviolet damage to plants about 500 times higher than
| normal. Ultraviolet radiation can cause mutations, cancer, and
| cataracts. It can kill plants or slow their growth, suppressing the
| photosynthesis which forms the base of the world's food chain.
|
| Smaller asteroid impacts, which have happened far more frequently in
| Earth's history, theoretically might cause similar or even worse
| problems with ultraviolet exposure, the researchers say. The ozone
| depletion would be less, but there would also be less of a protective
| dust cloud.
|
| "Part of what we're trying to stress here is that with an asteroid
| collision, there will be many synergistic effects on the environment
| that go far beyond the initial impact," said Cockell, a researcher
| with the British Antarctic Survey who did some of this analysis while
| formerly working with NASA. "Effects such as acid rain, fires, the
| dust clouds, cold temperatures, ozone depletion and ultraviolet
| radiation could all build upon each other."
|
| During the K-T event, the scientists said, many of the animals may
| actually have been spared most of the ultraviolet spring they
| envision. That impact, oddly enough, hit a portion of the Earth's
| crust that was rich in anhydrite rocks. This produced a 12-year
| sulfate haze that blocked much of the ultraviolet radiation. But it
| was a lucky shot -- that type of rock covers less than 1 percent of
| the Earth's surface.
|
| So when the next "big one" comes, the scientists said, the ecological
| repercussions may be more savage than any of those known in Earth's
| long history. The collision will be devastating, the "impact winter"
| deadly.
|
| But it will be the ultraviolet spring that helps finish off the
| survivors.
|