• Maybe supervolcano not to blame for our near-extinction

    NASA / GSFC / MITI / ERSDAC / JAROS, and the U.S./Japan ASTER Science Team

    About 70,000 years ago, the Toba supervolcano erupted in what is now Indonesia. After the eruption, the ground collapsed and left behind a depression called a caldera, which is not filled by Lake Toba and volcanic domes that have emerged in the
    time since, as seen in this set of images taken Jan. 28, 2006, by NASA's Terra satellite and then stitched together.

    By Charles Q. Choi
    LiveScience

    A supervolcanic eruption thought to have driven humanity extinct may not have endangered the species after all, a new investigation suggests.

    Supervolcanoes are capable of eruptions dwarfing anything ever seen in recorded history, expelling thousands of times more magma and ash than even a Mount St. Helens or Pinatubo. A supervolcanic eruption could wreak as much havoc as the impact of a mile-wide asteroid by blotting out the sun with ash, reflecting its rays and cooling the Earth — a phenomenon called a "volcanic winter." A dozen or so supervolcanoes exist today, some of them lying at the bottom of the sea.

    The largest supervolcano eruption of the past 2.5 million years was a series of explosions of Mount Tobaon the Indonesian island of Sumatra about 75,000 years ago. Researchers say Toba spewed out a staggering 700 cubic miles (2,800 cubic kilometers) of magma, equivalent in mass to more than 19 million Empire State Buildings. By comparison, the infamous blast from the volcanic Indonesian island of Krakatoa in 1883, one of the largest eruptions in recorded history, released about 3 cubic miles (12 cubic km) of magma.

    About the same time the eruption took place, the number of modern humans apparently dropped cataclysmically, as shown by genetic research. People today evolved from the few thousand survivors of whatever befell humans in Africa at the time. The giant plume of ash from Toba stretched from the South China Sea to the Arabian Sea, and in the past investigators proposed the resulting volcanic winter might have caused this die-off. [Countdown: History's Most Destructive Volcanoes]

    However, recently scientists have suggested that Toba did not sway the course of human history as much as previously thought. For instance, prehistoric artifacts discovered in India and dating from after the eruption hinted that people coped fairly well with any effects of the eruption.

    Now researchers have found that the evidence shows Toba didn't actually cause a volcanic winter in East Africa where humans dwelled.

    "We have been able to show that the largest volcanic eruption of the last 2 million years did not significantly alter the climate of East Africa," said researcher Christine Lane, a geologist at the University of Oxford.

    Ash in Africa
    Lane and her colleagues examined ash from Toba recovered from mud extracted from two sites at the bottom of Lake Malawi, the second largest lake in the East African Rift Valley.

    "We first started looking for the Toba ash a few years back, but it's a bit like looking for a needle in a haystack, so it took a while," Lane told OurAmazingPlanet. "Between myself and my co-author Ben Chorn, we systematically processed every centimeter of sediment between 24 to 46 meters (78 to 150 feet) depth in the central basin core. The layer is so small that if we leave any gaps in our search, we could miss it completely."

    Their analysis discovered that a thin layer of ash in this sediment about 90 feet (27 m) below the lake floor was from the last of the Toba eruptions, known as Youngest Toba Tuff.

    "The Toba super-eruption dispersed huge volumes of ash across much of the Indian Ocean, Indian Peninsula and South China Sea," Lane said. "We have discovered the layer of volcanic ash was carried about twice the distance as previously thought, over more than 7,000 kilometers (4,350 miles)."

    The amount of ash found in the Malawi sediment core (a cylindrical log of sediment drilled from the ground), was more than the scientists expected to find.

    "I was surprised to find so much ash in the Lake Malawi record," Lane added. "The ash is very tiny, composed of shards of volcanic glass smaller than the diameter of a human hair. Nevertheless, in a lot of records I have worked on previously, even within just a few hundreds of miles of an eruption center, we sometimes only find less than 100 shards of glass within a gram of sediment. In Malawi, we have thousands of shards of glass per gram, which really shows how voluminous the Youngest Toba Tuff was."

    Quick recovery
    If the area had seen dramatic cooling because of all the ash spewed into the atmosphere, living matter near the lake surface would likely have died off, significantly altering the composition of the lake's mud. However, when the researchers investigated algae and other organic matter from the layer that contained the ash from Toba, they saw no evidence of a significant temperature drop in East Africa. Apparently, "the environment very quickly recovered from any atmospheric disturbance that may have occurred," Lane said.

    But these results, detailed online April 29 in the journal Proceedings of the National Academy of Sciences, don't mean that super-eruptions aren't as big a risk to Earth's denizens as previously suggested.

    "It is important to realize that every volcanic eruption is different and the Youngest Toba Tuff provides only one example," Lane said. "The impact of an eruption depends not just on the amount of ash erupted, but also the composition and volume of aerosols, how high in the atmosphere the ash is injected and the meteorological conditions at the time."

    As for what might explain the near-extinction humanity apparently once experienced, perhaps another kind of catastrophe, such as disease, hit the species. It may also be possible that such a disaster never happened in the first place — genetic research suggests modern humans descend from a single population of a few thousand survivors of a calamity, but another possible explanation is that modern humans descend from a few groups that left Africa at different times.

    Future research will analyze what effects Toba may or may not have had on other lakes in East Africa.

    "Whilst from this we can hypothesize that the global climatic impact was not as dramatic as some have suggested, we will need to find similarly high-resolution records of past climate from other regions that also contain Youngest Toba Tuff in order to definitively test this," Lane said.

    Follow OurAmazingPlanet @OAPlanet, Facebook and Google+.Original article at LiveScience's OurAmazingPlanet.

    Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

  • Warming planet killing off cold-climate lizards, says study

    University of Exeter

    A cold-adapted Liolaemus belli lizard is shown here in the Andes near Farellones, Chile. Global warming threatens these species with extinction, according to a new study.

    By John Roach, Contributing Writer, NBC News

    Dozens of lizards that evolved the ability to give birth to live young in order to carve a niche for themselves in colder climates may become extinct as the planet warms over the next 50 years, according to new research.

    Since these lizards’ South American habitats are shrinking, the reptiles are forced to move up into the colder climes of the Andes, or down towards the South Pole. But as everything gets warmer overall, the lizards will find natural competition with warm-adapted reptiles who are expanding into these same areas. As a result, multiple extinctions could occur, says David Hodgson, an ecologist at the University of Exeter in England.

    The adaptation of live birth (viviparity) helped Liolaemus lizards such as the jewel lizard and the Chilean tree iguana find a niche in cooler spots that are less hospitable to more competitive lizards, ones that lay eggs (oviparity).

    Live birth "probably helps to cope with the effects of cold, or unpredictable, conditions on egg survival and embryo development," Hodgson explained in an email to NBC News.

    He and colleagues conducted research that indicates once lizards evolve viviparity, the process is irreversible, which appears to restrict them to cold climates.

    Why, exactly, viviparous reproduction constrains Liolaemus lizards to cold climates is uncertain, Hodgson noted, but it is possible that they are unable to compete with egg-laying lizards in warmer climates.

    Hodgson noted that viviparity exists in other lizard species that live on tropical islands elsewhere around the world, which suggests that climate alone is not a limiting factor in the survival of viviparous reptiles.

    "It would appear that viviparity is 'forced out' of warmer climates in South America by the more competitive oviparious species," he said. "But that is speculation."

    Hodgson and colleagues concluded March 5 in the journal Global Ecology and Biogeography that "viviparity has been largely responsible for the successful radiation of Liolaemus into cold climates, but ... (it) may prove to be an evolutionary dead-end for lizards facing rapid climate change."

    John Roach is a contributing writer for NBC News. To learn more about him, check out his website.

  • Half of Africa's lions could be gone in 40 years, conservationists warn

    Dan Kitwood / Getty Images stock

    Lion populations have been shrinking across Africa as they rub up against growing human populations. Herding cultures, such as the Maasai or the Zulu, may convert wild habitat to grazing land, thereby reducing the population of natural prey for the majestic cats.

    By Tia Ghose
    LiveScience

    Nearly half of all of Africa's lion populations could face extinction in the next 40 years if conservation measures aren't changed, according to a new study.

    The study, published Wednesday in the journal Ecology Letters, found that lion populations that were fenced into conservation areas rebounded in recent years, whereas lions in open preserves were challenged by prey loss and predation by human neighbors.

    "Lions in fenced reserves tend to do much better, they're achieving much better populations," said Luke Hunter, a conservation biologist with Panthera, an organization that works to protect endangered big cats. "It's also cheaper to achieve those outcomes."

    Big cats
    Lion populations have been shrinking — across Africa as they rub up against growing human populations. Herding cultures, such as the Maasai or the Zulu, may convert wild habitat to grazing land, thereby reducing the population of natural prey for the majestic cats. So instead of going after a zebra, lions will hunt people's livestock (and occasionally kill people).

    "More and more people live in fairly rural areas where there is wildlife, but those people rely on livestock, so they're really coming into conflict often with lions," Hunter told LiveScience. "They just see them as a really dangerous enemy." [In Photos: A Day in the Life of a Lion]

    To understand what strategies might best protect lions, Hunter and a few dozen colleagues analyzed lion population data from 42 sites across Africa. Some parks reported 46 years of data, whereas others had only three years of data.

    They then compared the population trajectories with fencing, the money allocated to conservation and nearby human population density.

    Fenced reserves cost a fourth of the cost to maintain and achieve the same results as unfenced reserves. Fenced reserves also had the highest lion numbers.

    Unfenced lions, by contrast, faced attacks by neighboring people, poaching and declining prey populations.  Nearly half of the populations will dwindle to near extinction levels in the next 20 to 40 years if no conservation measures are taken, the study showed.

    Don't fence us in
    But while the fencing is incredibly effective for preserving lions, not every conservationist loves them, Hunter said.

    "I would hate to see more of Africa fenced," Hunter said. "It just takes away from a sense of wilderness."

    Fencing can disrupt the great migrations of herbivores and the movements of free-roaming animals such as the African wild dog or the cheetah, he said. But it may be the most effective way to save lions, he said.

    "Whether it's a fence or some other form of barrier it's really clear that lions need physical separation from people if we're going to save them."

    Follow Tia Ghose on Twitter @tiaghose. Follow LiveScience on Twitter @livescience, Facebook or Google+. Original article on LiveScience.com. 

    Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

  • Humans alone to blame for wiping out Tasmanian tiger

    Courtesy of The Tasmanian National Museum and Gallery

    Tasmanian tigers (Thylacinus cynocephalus) looked somewhat like striped coyotes and were found throughout most of the Australian island of Tasmania before Europeans settled there in 1803.

    By Megan Gannon
    LiveScience

    Humans alone were responsible for the Tasmanian tiger's extinction in the 20th century, according to a new study that shoots down claims that disease also doomed the meat-eating marsupial.

    More officially known as thylacines, Tasmanian tigers (Thylacinus cynocephalus) looked somewhat like striped coyotes and were found throughout most of the Australian island of Tasmania before Europeans settled there in 1803.

    Starting at the end of the 19th century, the Tasmanian government paid bounties for thylacine carcasses, as the animals were believed to prey on farmers' sheep and poultry. (A recent study, however, showed that the carnivores' jaws were so weak they likely couldn't have taken down anything larger than a possum.) Humans eventually hunted thylacines to extinction in the early 1900s; the last known individual died in a Tasmanian zoo in 1936.

    "Many people, however, believe that bounty hunting alone could not have driven the thylacine extinct and therefore claim that an unknown disease epidemic must have been responsible," researcher Thomas Prowse of Australia's University of Adelaide said in a statement.

    Prowse and his colleagues developed a mathematical model to evaluate whether the combined impacts of Europeans' settlement could have wiped out the thylacine, without any disease involved.

    "The new model simulated the direct effects of bounty hunting and habitat loss and, importantly, also considered the indirect effects of a reduction in the thylacine's prey (kangaroos and wallabies) due to human harvesting and competition from millions of introduced sheep," Prowse said.

    Indeed, their results, published this month in the Journal of Animal Ecology, showed that these impacts alone would have been powerful enough to send the Tasmanian tiger population crashing in the early 20th century.

    A study out last year suggested that low genetic diversity eventually would have set the thylacine on a path to extinction even if they hadn't been hunted off the planet.

    The tiger's extant cousin, the Tasmanian devil, is currently being wiped out by a contagious cancer that's been able to spread all the easier because of the devil's low genetic diversity, which cuts down a wildlife population's ability to adapt to changing environmental conditions and bounce back from disease and mass fatalities. The Tasmanian tiger, if around today, also would be exceptionally susceptible to diseases, those researchers said.

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