Here's a researcher reporting that the livable period on earth is 90% over, suggesting that technolife just barely squeaked in under the wire:
 |
|
|
|
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 low graphics version | feedback | help | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
You are in: Sci/Tech: Specials: Washington 2000 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
Sunday, 20 February, 2000, 16:51 GMT
Date set for desert Earth
By BBC News Online's Damian Carrington in Washington DC The Earth is entering the final 10% of its lifespan, according to a US meteorologist.
However, well before the planet is left as an arid desert, the level of carbon dioxide in the atmosphere will be too low to support plant life, destroying the foundation of the food chains.
"The Sun, like all main sequence stars, is getting brighter with time and eventually temperatures will become high enough so that the oceans evaporate," said Dr Kasting. At 60 degrees Celsius (140 degrees Fahrenheit), water becomes a major constituent of the atmosphere. Much of this water drifts up to the stratosphere and is lost into space. Eventually, all the oceans will leak out of the Earth's grasp. Burnt-out planet "Astronomers always knew that the oceans would evaporate, but they typically thought it would occur only when the Sun left the main sequence - that will be in five billion years."
Stars leave the main sequence when they stop burning hydrogen. The Sun will then become a red giant, swamping and obliterating Mercury. Venus will lose its atmosphere and become a burnt-out planet.
"However, my calculations show the oceans may evaporate much earlier," said Dr Kasting. "They are somewhat pessimistic and present a worst-case scenario, but they say a billion years." The earlier loss of carbon dioxide will occur because as the climate gets hotter and wetter, more rock is weathered by rain. This dissolves carbon dioxide and hides it away on the ocean floor as calcium carbonate. "Obviously, a billion, even a half billion years, is a long way off in the future," said Dr Kasting. "But these models can help us refine our understanding of the time that a planet remains in an orbit where life can exist." "If we calculated correctly, Earth has been habitable for 4.5 billion years and only has a half billion years left." Dr Kasting's comments were made at the annual meeting of the American Association for the Advancement of Science. |
|
Links to other Washington 2000 stories are at the foot of the page.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mars: Will Earth look like this?
The Sun will consume Mercury
|
 Links to other Washington 2000 stories
|
 |
|
^^ Back to top News Front Page | World | UK | UK Politics | Business | Sci/Tech | Health | Education | Sport | Entertainment | In-Depth | Talking Point | Audio/Video |
We apparently got very lucky with the K-T boundary hit: http://www.sciencedaily.com/releases/2000/03/000313081731.htm Asteroid Devastation Could Even Be Worse Than Feared 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 o f 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 plane t 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 e nd 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 scena rio, 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 p enetration 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 agains t 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 would cause levels of ultraviolet radiation to at least double, about 600 days after impact." According t photosyntheto 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 th is 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-y ear 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.
Sounds like we're a bit lucky our beast isn't feeding: http://www.sciencedaily.com/releases/2000/03/000322091619.htm Astronomers Discover "Feeding" Mechanism For Black Holes COLUMBUS, Ohio -- Astronomers at Ohio State University used an innovative imaging technique to discover swirling masses of interstellar dust spiraling into the center of nearby galaxies. The researchers believe this interstellar dust is feeding supermassive black holes. Despite mounting circumstantial evidence that black holes occupy the heart of most galaxies, astronomers haven't seen compelling evidence of the material that might "feed" those black holes until now. Their study appeared in a recent issue of the Astronomical Journal. Using NASA's Hubble Space Telescope, Richard Pogge, associate professor of astronomy, and Paul Martini, astronomy graduate student, devised a plan to point two cameras -- one that records visible light and one that records infrared -- at nearby galaxies that may contain supermassive black holes. They combined infrared and visible-light images to create single images of the interstellar dust clouds in the centers of these galaxies. "Imagine if we could take a picture that showed only the dust in a galaxy," said Pogge. "We can't exactly do that, but we can get pretty close." The Hubble telescope enabled the Ohio State astronomers to zero in on the very center of 24 nearby spiral-shaped galaxies with extremely bright centers. Astronomers believe the centers of these galaxies are bright because they contain active supermassive black holes consuming matter from their surrounding galaxies. Astronomers call a black hole "active" when its powerful gravity tears material apart, releasing radiation and brightening the galaxy's center. Only 1 percent of galaxies that should contain supermassive black holes appear to be in an active state. Most pictures of these active galaxies show the giant arms of gas and dust that give spiral galaxies their shape. Pogge and Martini focussed instead on only the central 1,000 light years -- approximately 1 percent of the total diameter of these galaxies. "We looked at a region people were unable to study before," said Martini. Within 20 of the 24 galaxies they photographed, they saw a secondary, mini-spiral of dust that appeared to go directly into the center where the supermassive black hole resides. These "nuclear spirals" may be the feeding mechanism that activates black holes, Pogge and Martini said. Black holes like the one in our own Milky Way may be inactive, Pogge said, because they aren't receiving any nourishment from their host galaxy. "Before black holes become active, you have to feed them," Pogge said. And supermassive black holes have voracious appetites. Astronomers calculate that black holes must consume stars, gas, or dust in amounts up to the mass of our sun every year to remain active. Martini explained that over time the material in an inactive galaxy may reach an equilibrium in which it orbits the central black hole at a distance just out of the hole's reach. The black hole wouldn't receive any fuel, he said, until some kind of disturbance triggered an avalanche of material into the center. The disturbance could come in the form of a collision with ano propagate and have a very large effect." Pogge and Martini think the nuclear spirals form when material orbiting near the centers of , Pogge, Msse galaxies lack the mini-spiral structures seen in their brighter cousins.
This one looks significant, but I've no clue what to conclude: http://www.sciencedaily.com/releases/2000/03/000329080630.htm Meteoroid Bombardment Of Moon Has Intensified In Past 500 Million Years, Coinciding With Blossoming Of Life On Earth BERKELEY (3/9/00) -- A new chronology of meteoroid impacts on the moon shows some surprising correlations with major biological events on Earth. By dating minute glass beads thrown out by impacts over the millennia, scientists at the University of California, Berkeley, and the Berkeley Geochronology Center have not only confirmed expected intense meteor activity 4 to 3.5 billion years ago, when the large lunar seas or maria were formed, but have discovered another peak of activity that began 500 million years ago and continues today. The tapering off of the first peak of activity, which probably included many large comets and asteroids, coincides with the earliest know evidence of life on Earth. The second and ongoing peak, which from the evidence seems to have been mostly smaller debris, began around the time of the great explosion of life known as the Cambrian. "The first life on Earth arose just after this real crescendo around 3.5 billion years ago," said Paul R. Renne, adjunct professor of geology and geophysics at UC Berkeley and director of the Berkeley Geochronology Center. "Maybe life began on Earth many times, but the meteors only stopped wiping it out about 3 billion years ago." The more recent and ongoing activity is even more intriguing. "It's not surprising that the impacts tapered off about 3 billion years ago. The solar system was just getting cleaned up, primarily by Jupiter and the Sun," said Richard A. Muller, a professor of physics at UC Berkeley and a research physicist at Lawrence Berkeley National Laboratory. "What is surprising is the reversion from a benign to a violent solar system about 500 million years ago. "This work opens up a new field that tells us something about the history of our solar system that was totally unanticipated. Until now we did not realize how peculiar the past 500 million years has been." UC Berkeley graduate student Timothy S. Culler, along with Renne, Muller and Timothy A. Becker, laboratory manager at the Berkeley Geochronology Center, report their findings in the March 10 issue of the journal Science. Though all the Berkeley researchers agree on the new impact chronology for the moon, they have their own ideas about its implications. Renne, for example, leans toward the theory that interstellar dust seeded the Earth with organic molecules, from water to amino acids, that were incorporated into life on Earth during the past 500 million years. "Life already here would suddenly have a new stimulus, a greater need to evolve quickly and more raw material to do it," Renne said. "Impacts would have to be really, really big and really, really frequent to be deleterious to life on Earth, and it's clear that the flux over the past 500 million years has been relatively small objects. We don't see a lot of young large craters on the moon. We've come to accept the idea that impacts are strictly bad news for life on Earth, but now that's not so clear." Culler, the graduate student who originated the project under the supervision of Muller and Renne, sees the intense meteor activity as evidence that large meteor impacts played a major role in the evolution and extinction of life. "It shows that large impacts may have been more frequent in the last 500 million years, creating more extinctions, like the comet or asteroid that wiped out the dinosaurs 65 million years ago, " Culler said. "Even a number of smaller impacts can have a disastrous effect on the atmosphere and cause mass extinctions." Muller too emphasizes the role impacts have played in the history of life on Earth. It's not surprising that the recent intense period of meteor activity coincides with the rapid radiation of life on Earth, he said. "We're only beginning to realize the role played by catastrophe in the evolution of life," he said. "When it comes to survival of the fittest, it's not only the ability to compete with other species that counts, but also the ability to survive occasional catastrophe. That requires complexity and flexibility." Muller has proposed several controversial theories about the solar system, including that the sun has an unseen companion star, one he calls Nemesis, that orbits the sun every 26 million years and periodically knocks comets out of their orbits, sending them hurtling toward the inner solar system. He also has proposed that periodic climate changes are the result of the Earth's orbit periodically tilting up out of the orbital plane of the planets and intersecting a cloud of dust, debris and meteoroids. The current research was suggested by Muller in 1991, in part as a way to determine whether the moon's impact record shows evidence of a 26 million-year cycle. Muller hit upon the idea of argon-40/argon-39 dating of lunar spherules as a way to get a more precise chronology of the intensity of bombardment of the moon and, by implication, the Earth. "I realized that we didn't have to go to the individual craters in order to determine their age, because the craters sent samples to us," Muller said. "We could obtain samples of hundreds of different craters from just one location, without having the expense of going back to the moon. This idea is likely to open up a completely new round of lunar analysis." Spherules are mostly basaltic glass, Culler said, created when a meteor hits the surface and generates intense heat that melts the rock and splatters it outward. As droplets of molten rock fall back to the surface they quickly cool to form a glass, much like obsidian. Culler, Becker and Renne analyzed 155 beads from one gram of lunar soil picked up in 1971 by Apollo 14 from the Fra Mauro formation - a lunar highland bordering Mare Imbrium. The mineral composition of each bead was determined with a microprobe before it was laser melted and the argon gas captured for isotopic analysis. Contrary to assumptions, they found that the cratering rate on the moon has not been constant over its history. Approximately twice as many impacts occurred between 4 and 3 billion years ago as occurred between 2 and 1/2 billion years ago. About 500 million years ago the intensity of impacts increased nearly to what it was at the peak of activity 3.2 billion years ago. Though the dating method was not sensitive enough to reveal a 26 million-year cycle in th For the future, Renne says, it is "critical to launch new lunar sampling missions targeted to areas rich in potassium," in order to confirm the results and probe further back into the moon's history. The project was funded by the Ann and Gordon Getty Foundation, through the Berkeley Geochronology Center and Richard Muller. NASA provided the lunar samples.
From ionus@... Fri Mar 31 18:12:07 2000 To: cynbe@laurel.actlab.utexas.edu Subject: unusual solar composition brick Did we already discuss the apparent fact that the sun is 50-100% richer in metals than 'average' stars its age? I forget where this info comes from, but I've seen it cited as a well-established fact. If that's the case, it certainly is another 'order of magnitude' reducer in the complex life equation, since a metal-rich protostellar nebula is pretty clearly essential to the formation of earthlike planets. [...] David Studhalter The Radio Ionus News Service of Earth
(The 2000Jul Scientific American also notes that the Sun is unusually metal-rich.)
Physics News Update The American Institute of Physics Bulletin of Physics News Number 491, June 29, 2000, 2000 by Phillip F. Schewe and Ben Stein A Hofstra-Williams-Colgate-Manchester (UK) team of astronomers have used the National Radio Astronomy Observatory 12-m radio telescope to scan a huge molecular cloud only 30 light years from the galactic center. In particular they look at the spectra of hydrogen cyanide (HCN) and its deuterium counterpart DCN. In general stars are expected to be net consumers (not producers) of deuterium: they burn it into helium. But the galactic center is the Times Square of the Milky Way; it is the scene of jets, bursts, x-ray and gamma sources, a massive black hole, filaments, arcs, and other material-processing objects. From their observed ratio of deuterium-to-hydrogen D/H, the researchers (Don Lubowich, Jay Pasachoff, Tom Balonek, and Tom Millar) deduce three things: (1) The D/H ratio is higher than you would expect in the absence of a source of virginal unprocessed material (high in D, low in heavier elements). This demonstrates that matter comparatively rich in D is indeed raining down with the cloud onto the plane of our galaxy (see figure at Physics News Graphics). In other words, the infalling matter is to the galaxy what comets are to our solar system: specimens of relatively unprocessed, primitive material. (2) For all that, the D/H ratio at the galactic center is lower than in all other places in the galaxy. This is important evidence confirming that D is not made in stars and that what D we see is made by the big bang. (3) From models of D production in quasars, the observed D/H ratio suggests that the Milky Way could not have harbored a quasar for at least a billion years and probably not for four billion years. (Lubowich et al., Nature, 29 June 2000.)
2001-Feb-05: http://news.bbc.co.uk/hi/english/sci/tech/newsid_1154000/1154784.stm "Recent calculations of the Solar System's stability indicate that if the Earth was removed then Venus and Mercury would become destabilised in a relatively short time."
2001-02-16: http://www.cnn.com/2001/TECH/space/02/05/inbrief.020901/#1 Report: Giant planets may be key to life (CNN) -- The hunt for distant planets similar to Earth should concentrate on solar systems with planets the size of Jupiter, according to a new astronomical report. Such jovian giants could fling celestial objects the size of Mars toward their central star, transporting the water necessary for carbon-based life to form on smaller terrestrial worlds, planetary scientist Jonathan Lunine said last week. Scientific evidence strongly suggests a similar chain of events produced our own solar system, the University of Arizona researcher said. As the solar system formed, Jupiter's powerful gravity spurred asteroids to clump together into increasingly larger objects, prototypical rocky worlds, he said. Jupiter then tossed the terrestrial "embyros" into the inner solar system. Those that hit our planet carried the water that now fills Earth's oceans, according to the theory. The report by Lunine and his colleagues is in the January 30 issue of the Proceedings of the National Academy of Sciences.
This supports the notion that one rock hitting the right spot at the right time would have eliminated humans at almost any time but the last few millenia: EDINBURGH, Scotland (AP) -- Modern Europeans, and maybe populations in other parts of the world, are descended from no more than a few hundred Africans who left their homeland as recently as 25,000 years ago, new research suggests. Organization, the international collaboration researching the genetic makeup of the human race, provide the first estimate of how many people founded Europe. They are also a blow to the theory that modern humans evolved simultaneously in Africa, Europe and Asia from multiple early humans. "I think this certainly rules that out, at least in respect to Europe," said study leader Eric Lander, director of the Whitehead Institute/Massachusetts Institute of Technology Center for Genome Research. "We're not sure whether this was just the founding of Europe or whether, in fact, this small bottleneck represents all the people leaving Africa." Lander's study involved comparing about 300 chromosomes from people in Sweden, central Europe and Nigeria. The differences in the genetic pattern between the European and African chromosomes revealed how long ago Europeans left Africa and about how many there must have been. The pattern showed that the Europeans were descended from fewer ancestors than the Africans -- an evolutionary bottleneck, Lander said. "It's hundreds, not thousands," Lander said. The Nigerian chromosomes had been well shuffled around, which indicates a wide gene pool and a long breeding history, while the European chromosomes had long stretches of unshuffled genetic material, indicating a much smaller number of chromosome types entering the mix. Eddy Rubin, a scientist who was not involved in the study, said he thinks the findings are accurate. "The evidence is overwhelming that present-day Europeans come from a very small group that stayed small for a while, then expanded," said Rubin, head of the human genome center at the Lawrence Berkeley National Laboratory at the University of California, Berkeley. Lander said the findings had much broader applications. "We are going to be able to do this throughout much of the rest of the world. The data will be able to rule it in or out for the other populations very quickly," Lander said. "We're still in the early days for this, but it is remarkable how much the human chromosomes can be read as a history book," he continued. "We are going to be able to say how populations are related to each other, when people arrived there and how many people likely arrived in different places." The human race numbers 6 billion people today, but it largely has the genetic variation of a population of a few tens of thousands, Lander said. -- http://www.cnn.com/2001/TECH/science/04/20/human.origins.ap/index.html
More evidence of how amazingly closely synchronized human civilization
has been worldwide -- climate is the only obvious clock which could
have done this, suggesting just how critical favorable climate has
been to the development of technolife here:
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1298000/1298460.stm
Oldest civilisation in the Americas
Aerial view: Caral's huge central plaza, surrounded by large pyramids,
seen here as earth mounds An ancient city in what is now Peru was
built at the same time as the great pyramids of Egypt, archaeologists
have revealed.
New evidence indicates the desert site at Caral, on the slopes of the
Andes, was built between 2,600 BC and 2,000 BC.
This date pushes back the emergence of the first complex society in
the New World by nearly 800 years.
And it suggests that the people behind the project were advanced
enough to organise the labour needed to create the architectural
wonder of the day.
Caral is one of 18 sites in central Peru's Supe Valley, which
stretches eastward from the Pacific coastline, up the slopes of the
Andes.
Earth pyramids
All the inland settlements once had architecture on a grand scale,
including the six huge platform mounds seen at Caral.
Because of its size and complexity, archaeologists had thought Caral
was built about 1,500 BC.
But carbon dating of plant samples found at the site add another 1,000
years or so to this figure.
That puts Caral in the same period as the great pyramids of Egypt, and
long before the huge stone structures of Mexico.
"What we're learning from Caral is going to rewrite the way we think
about the development of early Andean civilisation," said study leader
Jonathan Haas of the Field Museum in Chicago, US.
The Peruvian-American archaeological team says the pyramids and
irrigation system show an organised society in which masses of people
were paid, or compelled, to work on centralised projects.
This suggests that power and wealth were held by an elite group at a
time when, in most of the Americas, people were still hunting and
gathering in much smaller communities.
'Power'
"The size of a structure is really an indication of power," said Haas.
"It means that leaders of the society were able to get their followers
to do lots of work."
What is surprising to archaeologists is that the city was created by a
society that had yet to invent pottery or cultivate grain.
Its people grew peppers, beans, avocadoes and potatoes - all of which
they roasted, having no pots to boil them in.
They also ate lots of anchovies, which may have been used in dried
form as a kind of currency, as grain was later.
The research is published in the journal Science.
http://www.sciencedaily.com/releases/2001/05/010504083512.htm
Latest Investigations Of Orion Nebula
Lower Odds Of Planet Formation
In 1993, when the Hubble Space Telescope surveyed the Orion nebula
for the first time, its images provided a substantial boost for the
argument that stars with planetary systems are commonplace in the
galaxy. Now, however, the most recent analyses of one the youngest,
closest and brightest nebulae cast doubt on that conclusion and suggest
that planets may be far rarer than astronomers have thought.
The Orion nebula is the closest example of a stellar nursery. Stellar
nurseries are special regions where the vast majority of new stars in the
galaxy are born. Interstellar clouds of molecular gas form, produce
thousands of new stars and then gradually dissipate. The nebula in
Orion is 1,500 light years from Earth and six light years or 35 trillion
miles across. It forms the second point of light in the hunter?s scabbard
in the Orion constellation. The Trapezium Cluster at the nebula?s
center contains more than 1,500 stars. Four massive young stars
illuminate the nebula, making it possible to observe many objects that
would normally be invisible. The starlight they produce is so intense, in
fact, that it ionizes thin layers of the gas in the region, producing a
rainbow of colors. So it?s not surprising that studies of Orion have
provided astronomers with some of the best information about the
process of star formation.
The first Hubble Space Telescope (HST) images found that up to 90
percent of the young stars in the nebula are surrounded by
"protoplanetary disks"-disks of dust and gas from which planets can
form. Astronomers call such star and disk systems "proplyds." Based on
the assumption that similar conditions prevail in other stellar nurseries,
the finding strengthened the hypothesis that planet production is a
common side effect of the star formation process.
C. Robert O?Dell, lead scientist on the first HST studies of Orion and
now a research professor at Vanderbilt University, has been studying
the nebula since 1964. In a May 1 presentation at the annual meeting of
the American Physical Society in Washington D.C., O?Dell reports
that the most recent studies of Orion appear to have come up with a
planet stopper. The youngest and brightest stars in the cluster are so
powerful that the ultraviolet radiation they produce should blast away
the dust and gas surrounding newly formed stars before they can form
planets.
"According to current estimates, it takes about 10 million years for a
planet to form," O?Dell says. "The massive, young stars in Orion are
more than 100,000 times as luminous as the sun. Our best estimate is
that these radiation levels can destroy a protoplanetary disk in a few
hundred thousand years. So it appears that most of the disks will be
gone long before planets can form."
A critical factor in this calculation is the length of time it takes planets
to develop. If planets form considerably faster than scientists currently
think, then the percentage of stars that develop planetary systems could
be substantially higher, O?Dell acknowledges.
Over the last eight years, O?Dell and W. J. Henney at the National
Autonomous University of Mexico at Morelia-working with graduate
students from Rice University and UNAM-have used a combination of
optical and radio telescope data to construct a detailed,
three-dimensional map of the nebula. Using this map, he estimates that
only 10 percent of the proplyds in the nebula are shielded from the
erosive star-shine.
If planetary formation times are correct, and the conditions in the
Orion nebula are typical of stellar nurseries, then only one star in 10 is
likely to form a planetary system, O?Dell says.
Why then does Orion contain more than 300 circumsolar disks? The
answer, according to O?Dell, is quite surprising. One of the stars in
Trapezium turns out to be a binary. By carefully measuring the
properties of this pair of stars, Francesco Palla at the Osservatio
Astrofisico di Arcetri in Italy and Steven Stahler at the University of
California, Berkeley have estimated that it can be no older than 100,000
years. Orion?s massive central stars must be even younger, O?Dell
contends, because they have created an intense radiation environment
that has essentially shut down star formation in the nebula.
"This estimate, combined with the fact that we don?t see any evidence
for depletion of the protoplanetary disks, even those exposed to the
highest radiation levels, suggests that the central stars are even younger,
perhaps only a few tens of thousands of years old," O?Dell says. The
fact that these stars may not be any older than mankind itself doesn?t sit
well with the astronomer. It goes against the Copernican principle.
Copernicus argued that the Earth wasn?t the center of the universe but,
rather, that the Earth orbits around the Sun. Since then this has been
generalized to the Copernican principle: There is nothing special in
time or space about Earth?s position in the universe.
"It is unlikely that homo sapiens and the Orion nebula should be formed
at just about the same time, but perhaps we are just lucky," O?Dell says.
By BBC News Online's Helen Briggs A mysterious disturbance in the forces at the heart of the Solar System could have triggered the asteroid that wiped out the dinosaurs. This intriguing new theory has been put forward by scientists who have calculated the paths of the planets over the past 100 million years. A US team believes a change in the dynamics of the Solar System caused Mercury, the Earth and Mars to veer off course. This could have pushed a giant asteroid towards our planet, spelling downfall for most living things, 65 million years ago. The idea has been floated by a team of astrobiologists at the University of California, Los Angeles (UCLA), based on simulations of the historical positions of the major planets. "Our best calculations show that the dynamical state of the inner Solar System changed abruptly about 65 million years ago," said Bruce Runnegar, director of UCLA's centre for Astrobiology. Chaos theory The event modified the average orbit of Mercury, Mars and the Earth in significant ways, he said, possibly perturbing asteroids in the inner part of the asteroid belt and throwing one or more of them into Earth-crossing orbits. "Thus, the ultimate cause of the K-T impact [and the demise of the dinosaurs] may have been caused by a chaos-induced change in Solar System dynamics," Dr Runnegar told BBC News Online. The basis of the theory, deduced by team members Ferenc Varadi and Michael Ghil, is chaos in the Solar System. Under this scenario, a small shift in the orbit of one or more planets could destabilise much of the Solar System. To test their theory, the researchers simulated the orbits of the major planets, working back in history over tens of millions of years. To their surprise, computer models pointed to a change in the dynamics of the inner Solar System at the time of the K-T (Cretaceous-Tertiary) mass extinction, about 65 million years ago, when many plants and animals suddenly became extinct. Dr Runnegar said they were now carrying out further studies to test their theory. "At the moment the link with the dinosaurs is based on a coincidence in time and a plausible mechanism," he added. 'Tenuous' link The research, presented at the Earth System Processes meeting in Edinburgh, UK, has received a mixed reaction from other experts. Professor Mark Bailey of the Armagh Observatory, Armagh, said the asteroid link appeared tenuous, but not impossible. "[It] relies not least on the assumption that the killer projectile was an asteroid and not a comet," he told BBC News Online. "Nevertheless, the idea that the resonant frequencies of the Solar System change chaotically on time-scales of tens to hundreds of millions of years (albeit only slowly and by relatively small amounts) is an interesting one which adds yet another wrinkle to the story of our changing Solar System." Professor Carlos Frenk, an astrophysicist at the University of Durham, UK, said the theory appeared plausible. "If these calculations are correct, they are very revealing of the unusual past behaviour of the Solar System," he told BBC News Online. "The past history of the Solar System was not as quiet as we thought - this very unusual chaotic behaviour may have happened on our doorstep."
http://www.abc.net.au/science/news/stories/s327749.htm ET can't call us if he's wet Thursday, 12 July 2001 The search for extra-terrestrial intelligence is probably a complete waste of time because any Earth-like planets harbouring life will be too wet to support the kind of technology needed to "speak" to us. That's the essence of a presentation expected to stimulate "spirited discussion" at an international conference on life in the universe, to be held at Sydney's Macquarie University today. The global effort to scan the cosmos for radio signals from intelligent beings on other planets is based on the belief that a myriad of earth-like planets exist which might harbour life wanting to let us know they are "out there". Other projects assume extra-terrestrials will communicate using modulated gravity waves, laser beams, and neutrino particles. But Melbourne planetary scientist Dr Nick Hoffman will tell the Astrobiology Australasia workshop that even the smartest beings could not develop the technology to support such communication systems if they were under water. In a poster presentation, La Trobe University's Dr Hoffman will reveal new calculations showing the odds of land forming on other Earth-like planets are "infinitesimally" small. Instead they would be landless waterworlds. "'Waterworlds are the most likely outcome of planet formation. If you?re in the sea, you cannot discover fire, so you cannot melt metal to build machinery, you cannot discover electricity and you cannot build computers," Dr Hoffman told ABC Science Online. "Sitting here, waiting for someone to 'phone' us up is a waste of time." The presence of land on our planet is a direct result of an extremely rare kind of collision with asteroids during its formation, Dr Hoffman says. This collision led to the formation of our unique type of moon, which is made of materially formerly part of the primitive Earth's outer crust. The dislodged crust created space on the planet's surface into which oceans could drain. Without that space, the entire surface of the Earth would be covered with water, except for the tops of the highest mountains which would have been eroded by waves. Dr Hoffman conceded that searching for life in the universe "gave people something to look forward to" and so probably did no harm. But he felt the only real way to discover other civilisations was to "go there, land on their waterworld and see them."
http://www.sciencedaily.com/releases/2002/01/020109074626.htm
Source:
Johns Hopkins University (http://www.jhu.edu)
Date:
Posted 1/9/2002
Ancient Supernova May Have Triggered Eco-Catastrophe
An exploding star may have destroyed part of Earth's protective ozone
layer 2 million years ago, devastating some forms of ancient marine
life, according to a new theory presented at this week's meeting of
the American Astronomical Society.
The new theory brings together puzzling clues from several different
fields of research, including paleontology, geology and astronomy.
Narciso Benitez, an associate research scientist in astronomy in the
Krieger School of Arts and Sciences at The Johns Hopkins University,
says the "missing smoking gun" that brought the clues together was the
revelation that a stellar cluster with many large, short-lived stars
prone to producing supernovae had passed near Earth's solar system
several million years ago.
That discovery, made by co-author and Space Telescope Science
Institute astronomer Jesus Maiz-Apellaniz, led Benitez to check the
scientific record for potential effects of nearby supernovae on the
Earth.
"Nobody had realized that this cluster of stars that Jesus had
tracked, which is known as the Scorpius-Centaurus OB association,
could have been so close to Earth during the past several million
years," Benitez says. "And when I did a search, one of the first
things that popped out was a 1999 finding where a team of German
astronomers led by Klaus Knie detected the presence of a highly
unusual isotope of iron in samples of the Earth's crust drilled from
the deep ocean bottom."
Knie had proposed that the iron isotope was debris from a recent
supernova explosion that took place close to Earth. But astronomers
had no plausible candidates for such a nearby explosion until
Maiz-Apellaniz's work with the Scorpius-Centaurus association, which
is also being presented at this week's meeting of the American
Astronomical Society.
Benitez compared data produced by Maiz-Apellaniz and Knie's results,
and found "very good agreement, both in the amount of iron deposited
and in its time distribution."
Benitez consulted with his wife, Matilde Canelles, an immunologist at
the National Institutes of Health who had done her master's thesis on
microscopic algae, to learn if the paleontological record included an
extinction that had unusual characteristics suggestive of a potential
link to a supernova.
"Such an extinction would have had especially pronounced effects on
the plankton and the marine organisms," Benitez explains.
Canelles pointed out that evidence existed for a widespread extinction
of plankton and other marine organisms about 2 million years ago, and
noted that scientists are still debating the possible causes of the
event.
"Based on the minimal distance we expected for a supernova in the
Scorpius-Centaurus association at that time, I then did some
calculations to explore the potential effects on Earth," says Benitez.
He found that cosmic ray emissions from a supernova could have had a
potentially devastating effect on the Earth's ozone layer, an upper
layer of the atmosphere that absorbs harmful ultraviolet emissions
from the sun and other sources.
"This would have produced a significant reduction in phytoplankton
abundance and biomass, with devastating effects on other marine
populations, such as bivalves," Benitez says.
Benitez emphasizes that the theory, while provocative, is consistent
with the paleontological evidence, and also with the pattern of
movement of the Scorpius-Centaurus group, which would have been at its
closest to Earth at that time.
He concedes, though, that more evidence will be needed to firmly
establish the theory. In particular, more detailed searches for
supernova-produced isotopes in the geological record would show
whether there was a tight temporal correspondence between the
supernova explosion and the extinction event. Isotope searches could
also offer crucial information about the physical processes involved
in supernova explosions.
"People study supernovae using telescopes and supercomputer
simulations. In the future, some of the most relevant information in
this field may be found in the deep ocean floor," says Benitez.
While the new theory may further heighten concern about human impacts
on the ozone layer today, Benitez and Maiz-Apellaniz say there's no
need to worry about another supernova in the Scorpius-Centaurus group
affecting Earth in the near future. The next star due to explode in
the association, Antares, is now located at a distance of almost 500
light-years, which is too far away to have a significant effect on our
planet.
This research was funded by an Advanced Camera for Surveys grant from
NASA, the Johns Hopkins Center for Astrophysical Sciences, and a grant
from the Space Telescope Science Institute.
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1975000/1975354.stm
Cosmic catastrophe 'a certainty'
By Dr David Whitehouse BBC News Online science editor
Sooner or later, a catastrophe from space will wipe out almost all
life on Earth.
According to Dr Arnon Dar, of the Technion Space Research Institute,
Israel, a particular type of exploding star going off anywhere in our
region of the Universe would devastate our planet.
Using the latest statistics and calculations, he argues that a
supermassive star collapsing at the end of its lifetime would form a
black hole and send out a beam of destructive radiation and particles
that would sterilise any planet in its path.
The odds are that any planet in our galaxy would be affected about
once every one hundred million years. "It is a certainty; the
timescales are comparable to mass extinctions seen in Earth's
geological record," Dr Dar told BBC News Online.
No hiding place
Supermassive stars, those with a mass substantially greater than our
Sun, are scattered throughout the galaxy. It is thought that when they
collapse at the end of their lives, they eject an intense beam of
radiation, called gamma-rays, into space.
So powerful are these gamma-rays, and the energetic sub-atomic
particles that follow in their wake, that they could have a major
influence on life in our galaxy.
"If such a beam were to strike Earth, the effects would be totally
devastating, unlike anything we could imagine," Dr Dar said.
On the side of Earth facing the explosion, searing shock waves will
begin to rip through the atmosphere igniting infernos when they reach
the ground.
Within moments of the arrival of the radiation from deep space, the
atmospheric temperature will begin rising rapidly, wreaking havoc with
global weather systems.
Destructive 'daughters'
All organic material on the surface of Earth will start to burn.
Survivors will cower in caves and buildings. But the worst is yet to
come.
The initial gamma-ray burst will last a fraction of a second. Almost
immediately afterwards will come the cosmic rays, which will drench
our planet for days. There will be no hiding place.
Cosmic rays are highly energetic particles travelling through space at
almost the speed of light. They will slam into the atmosphere,
depositing vast amounts of energy and creating swarms of destructive
"daughter" particles.
These particles, called muons, will penetrate hundreds of metres into
rocks so that few caves will offer protection and even deep-sea
creatures will be affected by lethal doses of radiation.
The Earth's ecosystem will be destroyed. "The few who might survive
will wish they had died," said Dr Dar. "They will struggle, forlornly,
on a wrecked planet."
Dr Dar points out that many of the great extinctions that regularly
punctuate the Earth's history are consistent with being caused by a
devastating influx of radiation from space.
Threatening stars
"Direct proof that it happened this way is lacking at present," he
said, "but many people are looking for it."
There is some good news! Because the gamma-ray bursts from collapsing
supermassive stars are shot across the cosmos in narrow beams,
probably no more than a degree across, most of them will miss the
Earth.
However, the latest statistics suggest once every one hundred million
years or so, we will be unlucky. Curiously, this is about the rate of
global extinctions on Earth.
At the moment, astronomers do not know which star to watch. Stars,
like the supermassive Eta Carinae, visible in the Southern Hemisphere,
are likely to explode and send out a gamma-ray burst sometime in the
next million years or so. But this particular star is not pointing in
our direction.
Undoubtedly, there is a star that is, but as yet astronomers have not
found it. But even if they do, will we get any warning?
"Not with our current understanding of science," said Dr Dar, "but
then science progresses. Perhaps, one day we will be able to tell
which stars are threatening."
http://www.space.com/scienceastronomy/astronomy/goldilocks_zone_020528-1.html
Amid the Universe's Chaos, a Few Habitable Places
By Robert Roy Britt Senior Science Writer posted: 07:00 am ET 28 May
2002
It took 4.5 billion years for Earth to generate and evolve a life form
that could think, reason, and finally fly off the planet. That's a
long time, even by cosmic measures. Perhaps too long.
At a time when the only known sentient species has earnestly and
optimistically begun to search for life on other planets, several
scientists within that species have found a host of reasons to guard
the optimism. Throughout the galaxy, hazards to planet formation and
sustained evolution are so serious and varied that life may be
exceedingly rare. Intelligent life, presumably, would be the rarest of
all.
We may, it turns out, be very lucky to be here. However, we may also
turn out to be very alone.
Location, location, location
Guillermo Gonzalez, an Iowa State University expert in stellar
evolution, says there are relatively small bands and patches of the
Milky Way Galaxy that he considers to be habitable regions. There are
places where conditions are just right for the formation of planets
and where things stay calm enough, long enough, to allow the evolution
of anything but the lowest forms of life.
Our Sun happens to be in one of these Goldilocks zones. For now, at
least.
Gonzalez has examined the structure of the galaxy and the amount of
heavy elements distributed through it. The central region of the
galaxy, he says, is far to cramped and chaotic to expect Earth-like
planets to have much chance of developing and remaining stable.
Planetary systems, if they are like ours, are expected to include
outer belts of comets, like our own Oort cloud which extends beyond
Pluto. Near the center of the galaxy, which all astronomers agree is
more densely packed with stars, close encounters between stars would
gravitationally boot more of these comets into the inner reaches of a
solar system, where the planets would be.
Further, because there is a greater concentration of heavy elements --
carbon, iron and other stuff that weighs more than hydrogen and helium
-- near the galactic center, Gonzalez said more comets and asteroids
would probably develop.
"Comet showers should be more common," Gonzalez said at a meeting
titled "Astrophysics of Life" earlier this month at the Space
Telescope Science Institute (STScI).
Conversely, the outer reaches of the galaxy are relatively lean in the
heavier elements, making planet formation difficult according to
present theories. Other researchers have doubted this assertion,
suggesting that regardless of the abundance of heavy elements in a
star's environment, the quantities can vary greatly within a solar
system, as has been observed in our own.
Galactic Habitable Zone
There are other hazards, however. The pronounced spiral arms of the
Milky Way are regions where star formation is more frequent and
intense. As with the center of the galaxy, gravitational chaos and
heavy radiation in the arms is not conducive to long-running
biological evolution.
Between the spiral arms is the only safe place, Gonzalez has been
saying in recent years.
However, while stars orbit the galactic center, they are all on
different courses in relation to the spiral arms and the main, fairly
flat disk of the galaxy. Some stars, during their lifetimes, cross the
spiral arms, and others do not. Other stars travel above, below and
perilously through the main plane.
The Galactic Habitable Zone, which it has come to be called is, then,
actually several shifty places whose bounds are as-yet unclear.
"We don't know where it is exactly," Gonzalez said. "We think it's in
the thin disk of the galaxy. It excludes the center of the galaxy, and
it excludes the outer edge of the galaxy."
And where are we?
"We're between spiral arms. We're going to stay between spiral arms
for a long time."
Though Gonzalez figures the Sun "undoubtedly" experienced more
dangerous regions of space in the past, he says it isn't possible to
figure out where we were prior to a few hundred million years
ago. What he does know is that our solar system moves around the
galaxy at a pace and direction that is similar to the nearest spiral
arms, so we will not soon crash through one or be overtaken.
Bully stars
Like Gonzalez, John Bally would love to know where the Sun was
born. Bally, of the University of Colorado, examines the birthplaces
of stars and has learned that the vast majority are generated from
giant clouds of hydrogen that spawn not one, but many stars in a huge
and dense nursery of nearly simultaneous birth.
It's anything but a pleasant womb.
The clusters are violent, chaotic places whose largest stars --
superhot, massive, short-lived objects -- bathe the smaller ones in
heavy doses of ultraviolet radiation that can destroy the seeds of
planets before they ever form.
Here's what happens:
When stars form, some or perhaps most leave a circle of debris -- gas
and dust -- that develops into rotating mass called a protoplanetary
disk. From this material, planets, asteroids and comets are thought to
form. At least that's how it probably happened in our solar
system. Scientists are only beginning to spot and study these dusty
disks around other, relatively nearby stars, and they've seen clumps
that hint at planets in the making.
But nearby stars share the relative calm pocket of space -- one of
Gonzalez's habitable zones -- that our Sun benefits from. Most star
formation occurs in clusters, and it the bulk of it takes place in the
spiral arms.
In these clusters, a few massive stars shine thousands or even
millions of times more brightly than our Sun. Their UV radiation eats
away at the dust disks of other stars, and can strip the planetary
seeds from all nearby stars over the course of a million years or
less.
Meanwhile, other wild interactions are taking place in the dense star
clusters. When a cloud of hydrogen forms stars, it does so because it
contracts and begins to spin. Clumps of greater density form here and
there, Bally explained, and these clumps gain spin and collapse to
form stars.
"Nearby interactions with multiple stars in a rich cluster can
truncate and even completely eliminate protoplanetary disks," Bally
said.
All the while, the rotation and gravitational forces can fling stars
hundreds of light-years from their birthplaces. After a few million
years, many of the stars escape the worst radiation environments. And
the large, bully stars pay a price for all their energetic activity --
they typically die within 40 million years.
In an interview, Bally said his research and that of others shows that
around most stars, there is a tight time constraint on when planets
must form before the star's dust disk is blown away.
"I'm not saying planets can't form," he said. "But you have only
100,000 years to a million years."
Given the roughly 300 billion stars in our galaxy, Bally's limits
would still allow for plenty of planets out there, but it could also
mean there are far fewer than some researchers have expected. "Either
planetary systems form very fast," Bally said, "or we will find planet
development to be rare. Something like 5 percent of stars will have
planets."
However, if a planet can form quickly -- and theorists are not sure
just how long this process takes -- then the radiation is irrelevan