Astrophysics and extinctions: News about planet-threatening events

ScienceDaily (Oct. 7, 2011) — Space is a violent place. If a star explodes or black holes collide anywhere in our part of the Milky Way, they'd give off colossal blasts of lethal gamma-rays, X-rays and cosmic rays and it's perfectly reasonable to expect Earth to be bathed in them. A new study of such events has yielded some new information about the potential effects of what are called "short-hard" interstellar radiation events.

Several studies in the past have demonstrated how longer high-energy radiation bursts, such as those caused by supernovae, and extreme solar flares can deplete stratospheric ozone, allowing the most powerful and damaging forms of ultraviolet radiation to penetrate to Earth's surface. The probability of an event intense enough to disrupt life on the land or in the oceans becomes large, if considered on geological timescales. So getting a handle on the rates and intensities of such events is important for efforts to connect them to extinctions in the fossil record.

"We find that a kind of gamma ray burst -- a short gamma ray burst -- is probably more significant than a longer gamma ray burst," said astrophysicist Brian Thomas of Washburn University. Improved and accumulated data collected by the SWIFT satellite, which catches gamma ray bursts in action in other galaxies, is providing a better case for the power and threat of the short bursts to life on Earth.

The shorter bursts are really short: less than one second long. They are thought to be caused by the collision of two neutron stars or maybe even colliding black holes. No one is certain which. What is clear is that they are incredibly powerful events.

"The duration is not as important as the amount of radiation," said Thomas. If such a burst were to happen inside the Milky Way, it its effects would be much longer lasting to Earth's surface and oceans.

"What I focused on was the longer term effects," said Thomas. The first effect is to deplete the ozone layer by knocking free oxygen and nitrogen atoms so they can recombine into ozone-destroying nitrous oxides. These long-lived molecules keep destroying ozone until they rain out. "So we see a big impact on the ozone layer."

Those effects are likely to have been devastating for many forms of life on the surface -- including terrestrial and marine plants which are the foundation of the food web.

Based on what is seen among other galaxies, these short bursts, it seems that they occur in any given galaxy at a rate of about once per 100 million years. If that is correct, then it's very likely that Earth has been exposed to such events scores of times over its history. The question is whether they left a calling card in the sky or Earth's geological record.

Astronomical evidence is not likely, said Thomas, because the galaxy spins and mixes pretty thoroughly every million years, so any remnants of blasts are probably long gone from view. There might, however, be evidence in the ground here on Earth, he said. Some researchers are looking at the isotope iron-60, for instance, which has been argued as a possible proxy for radiation events.

If isotopes like iron-60 can reveal the strata of the events, it then becomes a matter of looking for extinction events that correlate and seeing what died and what survived -- which could shed more light on the event itself.

"I work with some paleontologists and we try to look for correlations with extinctions, but they are skeptical," said Thomas. "So if you go and give a talk to paleontologists, they are not quite into it. But to astrophysicists, it seems pretty plausible."

Thomas will be presenting his work on October 9, 2011, at the annual meeting of the Geological Society of America in Minneapolis. This work was supported by the NASA Astrobiology: Exobiology and Evolutionary Biology Program.

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Astrophysics and extinctions: News about planet-threatening events

ScienceDaily (Oct. 7, 2011) — Space is a violent place. If a star explodes or black holes collide anywhere in our part of the Milky Way, they'd give off colossal blasts of lethal gamma-rays, X-rays and cosmic rays and it's perfectly reasonable to expect Earth to be bathed in them. A new study of such events has yielded some new information about the potential effects of what are called "short-hard" interstellar radiation events.

Several studies in the past have demonstrated how longer high-energy radiation bursts, such as those caused by supernovae, and extreme solar flares can deplete stratospheric ozone, allowing the most powerful and damaging forms of ultraviolet radiation to penetrate to Earth's surface. The probability of an event intense enough to disrupt life on the land or in the oceans becomes large, if considered on geological timescales. So getting a handle on the rates and intensities of such events is important for efforts to connect them to extinctions in the fossil record.

"We find that a kind of gamma ray burst -- a short gamma ray burst -- is probably more significant than a longer gamma ray burst," said astrophysicist Brian Thomas of Washburn University. Improved and accumulated data collected by the SWIFT satellite, which catches gamma ray bursts in action in other galaxies, is providing a better case for the power and threat of the short bursts to life on Earth.

The shorter bursts are really short: less than one second long. They are thought to be caused by the collision of two neutron stars or maybe even colliding black holes. No one is certain which. What is clear is that they are incredibly powerful events.

"The duration is not as important as the amount of radiation," said Thomas. If such a burst were to happen inside the Milky Way, it its effects would be much longer lasting to Earth's surface and oceans.

"What I focused on was the longer term effects," said Thomas. The first effect is to deplete the ozone layer by knocking free oxygen and nitrogen atoms so they can recombine into ozone-destroying nitrous oxides. These long-lived molecules keep destroying ozone until they rain out. "So we see a big impact on the ozone layer."

Those effects are likely to have been devastating for many forms of life on the surface -- including terrestrial and marine plants which are the foundation of the food web.

Based on what is seen among other galaxies, these short bursts, it seems that they occur in any given galaxy at a rate of about once per 100 million years. If that is correct, then it's very likely that Earth has been exposed to such events scores of times over its history. The question is whether they left a calling card in the sky or Earth's geological record.

Astronomical evidence is not likely, said Thomas, because the galaxy spins and mixes pretty thoroughly every million years, so any remnants of blasts are probably long gone from view. There might, however, be evidence in the ground here on Earth, he said. Some researchers are looking at the isotope iron-60, for instance, which has been argued as a possible proxy for radiation events.

If isotopes like iron-60 can reveal the strata of the events, it then becomes a matter of looking for extinction events that correlate and seeing what died and what survived -- which could shed more light on the event itself.

"I work with some paleontologists and we try to look for correlations with extinctions, but they are skeptical," said Thomas. "So if you go and give a talk to paleontologists, they are not quite into it. But to astrophysicists, it seems pretty plausible."

Thomas will be presenting his work on October 9, 2011, at the annual meeting of the Geological Society of America in Minneapolis. This work was supported by the NASA Astrobiology: Exobiology and Evolutionary Biology Program.

Recommend this story on Facebook, Twitter,
and Google +1:

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Geological Society of America.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Numbers flap has minor implications for global extinctions

Statistical technique inflates predictions of species disappearances, two ecologists chargeWeb edition : Thursday, May 19th, 2011 LOST Carolina parakeets are one of several bird species that have gone extinct in the eastern United States in a complicated relationship of extinction numbers and habitat shrinkage that ecologists are still debating.John James Audubon

Two ecologists have poked a hornet’s nest by contending that a long-overlooked flaw in one form of analysis has inflated estimates of looming species extinctions.

Correcting the flaw wouldn’t change the basic projection that extinctions will be massive, says one of the ecologists, Stephen Hubbell of UCLA. Even so, he and a colleague write in the May 19 Nature, the problem requires revisions in a technique that ecologists use to estimate species extinctions due to habitat destruction.

Outspoken ecologists have already dismissed the work as technical quibbling that threatens to distract attention from the most cataclysmic loss of biodiversity in at least 65 million years. A long-time thinker about extinctions, Stuart Pimm of Duke University, objects to the paper as “truly disastrous.” He says it does advance understanding on a technical point but ignores bigger issues and practices among extinction predictors. “This is going to be the biggest bun-fight in my profession in a very long time,” Pimm says.

But Hubbell insists that he is raising a scientifically substantive issue: “Come hell or high water, we have to be self-correcting. Or why are we doing science?”

Behind the flying baked goods is a long-standing observation, formalized in a standard species-area relationship equation, that bigger areas support a greater number of species than smaller areas do. Hubbell, Pimm and other ecologists agree that humanity’s accelerating destruction of other species’ habitats has become a major force squeezing species into extinction. What they disagree on is how to quantify that process.

The equation that ecologists use to estimate how many species could disappear if a given area is, say, turned into city sprawl has roots in surveys of how many kinds of organisms crowd into an area. A biologist counting all the species in an area has to tramp just far enough to find the first of its kind before adding that name to the list. A species-area relationship based on such data predicts that even a relatively modest land loss dooms a whole species.

Another approach is to find the outer limits of an organism’s range, but that requires traversing much more area than it would take to find one example of a species. Either way, species living only within a surveyed area, considered endemic to that area, are those at immediate risk of going extinct. The new paper proposes focusing on endemics for a more realistic view of what habitat loss might do to the number of species in an area.  

“It’s embarrassingly simple,” says Hubbell, who discovered the flaw in collaboration with Fangliang He of Sun Yat-sen University in Guangzhou, China, and the University of Alberta in Edmonton, Canada.

To test this possible flaw in count-the-first-one surveys, Hubbell and He turned to detailed tree data from eight forest patches and two sets of bird data with substantial information on the birds’ ranges. Indeed, the traditional count-the-first surveys didn’t do a good job of reflecting how much area endemic species covered. The discrepancy could cause the standard species-area relationship to add an extra 160 percent to estimates of species loss. To use the better, endemic-based method to project losses of an area’s species from amoeba to zebra, though, “we need a lot more data,” Hubbell says.

What the new paper will mean, if anything much, for the practice of estimating extinctions is the question that launches a thousand, often disputative, buns.

Such a high-profile attack about a technical issue “is going to set us back a long, long time,” says Michael Rosenzweig of the University of Arizona. Estimates of extinction need to account not just for endemic species in an area that get their whole world trashed when the habitat goes but species that may have lost thriving populations that provided sources of immigrants for iffier habitats.

One prominent extinction estimate that Hubbell and He call into question comes from the 2005 Millennium Assessment, which predicted extinction rates in coming years as much as 1,000 to 10,000 times higher than the ho-hum background rates seen during times of relatively mild, natural change in life on Earth.

“It is true that in the 1980s and early 1990s, essentially all estimates of extinction rates were indeed based on species-area relations,” says Robert May of the University of Oxford in England. But more recent estimates, including the work behind the Millennium Assessment, draw on multiple lines of evidence, he says.

“All ways that we measure extinction, not just species-area relationships, point to [extinction] rates that are elevated today,” says paleobiologist Anthony Barnosky of the University of California, Berkeley. In March he and his colleagues published an analysis — not based on species-area relationships — suggesting that ongoing extinctions could within the next few centuries grow to proportions qualifying as the sixth of Earth’s historical mass extinctions. Even using Hubbell and He’s adjustments to dial back a recent high-profile prediction of 18 percent to 35 percent land species losses from climate change could still means losing 10 percent in the not-too-distant future. That’s “an unacceptably high loss by anyone's standards,” he says.

Broadly speaking, the exact scale of estimated extinctions may not matter much, says plant scientist Vernon Heywood of the University of Reading in England. “Today no one doubts that species extinction is a major issue, and the real debate is about how we are to prevent a further substantial loss of biodiversity,” he says. “That is more about politics and economics than precise modeling.”

Found in: Earth, Environment and Life

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Extinctions breed carbon chaos

Massive die-offs left ecosystems vulnerable, analysis suggestsWeb edition : Friday, February 4th, 2011

Big extinctions don’t just wipe out a lot of species. They also send ecological cycles reeling for millions of years, a new study suggests.

Following massive die-offs, the natural processes that keep carbon flowing through marine ecosystems — from tiny photosynthesizers to big fish and between the bottom and the top of the ocean — get broken. For millions of years after at least two global disasters, marine communities were too unstable to keep the molecules churning, researchers report in the February issue of Geology. These “chaotic carbon episodes” could have big ramifications for extinctions in the modern era, say scientists from Brown University in Providence, R.I., and the University of Washington in Seattle.

 In healthy marine ecosystems, diverse swimming predators, lazy filter feeders and myriad other organisms keep the carbon flowing nonstop, says study coauthor Jessica Whiteside, a paleobiologist at Brown.  But after a global extinction, when only a few plants, animals or single-celled critters occupy each rung of the food chain, minicatastrophes like diseases or climatic shifts take big tolls, she says. “If you already have a weakened state of ecosystems, these things that would normally be minor variations now become wildly oscillating,” she says. 

The team looked particularly at the diversity of ancient octopus-like animals called ammonites, which were ultimately wiped out by the same extinction that killed the dinosaurs. Ammonites often swam to catch prey as well as floated idly, snagging debris from ocean currents. But for millions of years after the end-Permian mass extinction 250 million years ago, as well as after the end-Triassic mass extinction 50 million years later, few swimming ammonites survived.

The devastation of ammonites and other life forms left its mark on the geologic record, Whiteside says. Scientists recognize five mass extinctions in Earth’s history. The worst — the end-Permian extinction — killed about 90 percent of ocean-dwelling species. Scientists discovered that after most of these calamities carbon molecules in the environment, on average, got lighter. The culprits behind this drop are major volcanic events like those associated with the end-Permian mass extinction. Volcanoes spew a relatively high proportion of lighter isotopes of carbon — atoms with fewer neutrons in their nuclei — into the atmosphere, says Jean Guex, a paleobiologist with Lausanne University in Switzerland.

“They are not volcanoes like people imagine,” says Guex, who was not involved in either study. “They are fissures which are extruding millions of cubic kilometers of basalts, inducing major atmospheric pollutions with sulfur and heavy metals.”

Tiny photosynthesizers gobble down the lighter carbon in the air, introducing it to the environment and, eventually, the geologic record. In a normally functioning ecosystem, that would cause the proportion of light carbon isotopes in the record to lighten and then eventually return to normal. But when Whiteside’s team eyed carbon isotopes in sedimentary layers from the periods following the end-Permian extinction and the end-Triassic extinction, carbon weights jumped back and forth from heavier to lighter isotopes. She argues that ecosystem instabilities could easily have triggered these wild fluxes. As living organisms died, they floated to the ocean bottom, carrying the lighter carbon molecules in their bodies with them. That left the carbon in the surface waters, on average, heavier, she says. When communities rebounded, carbon weights in the upper oceans dropped back down.

But Guex says that the real chaotic factor in this picture was the environment, not the carbon flows. Undersea volcanoes erupted on and off for millions of years following each extinction event, he argues. “The carbon isotopes mainly reflect these crises.”

Whiteside agrees that such churning could have played a role but cautions against ignoring the ecological factors. Minor volcanic eruptions would have affected weak communities much more than strong ones, she says. 

The team’s conclusions are particularly relevant for the modern era — what many biologists have dubbed the sixth mass extinction, Whiteside notes. Computer simulations of climate change look 100 years into the future, but the impacts of species extinctions today may last long after human pollution has come and gone, she says. “It’s a cautionary tale for the species loss that’s going on right now.”

Found in: Earth and Environment

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