National geographic article iceman,national geographic channel in tamil programs,survival list for 1 month - Try Out

A quarter of a billion years ago, long before dinosaurs or mammals evolved, the 10-foot (0.3-meter) predator Dinogorgon, whose skull is shown here, hunted floodplains in the heart of today's South Africa. National Geographic explores how we can feed the growing population without overwhelming the planet in our food series. Volunteers risk their lives to vaccinate children in Islamic State-controlled territory in Syria.
In less than a million years Dinogorgon vanished in the greatest mass extinction ever, along with about nine of every ten plant and animal species on the planet. Decades of acid rain generated by power-plant emissions have devastated the region's ecosystems. About 250 million years ago, at the end of the Permian period, something killed some 90 percent of the planet's species. Looy had told me that the Black Triangle was the best place today to see what the world would have looked like after the Permian extinction. This didn't look like apocalypse.We saw the first signs of death as we walked into the hills—hundreds of fallen timbers lay hidden in the undergrowth.
Half a mile (0.8 kilometers) uphill we found the trunks of a stand of spruce, killed by acid rain. The only sound was the wind through the acid-tolerant weeds."The forest that grew here a few decades ago contained dozens of species of plants," said Looy. She believes that the Permian extinction was caused by acid rain following a massive release of volcanic gases. She wants to compare tree pollen from a modern forest killed by acid rain with fossil pollen found in Permian rocks.Like a homicide detective at a crime scene, Looy sealed the cone in a plastic bag for later lab work.
The most famous die-off ended the reign of the dinosaurs 65 million years ago between the Cretaceous and Tertiary periods. Rocks of that age contain traces of an asteroid that struck Earth, generating catastrophic events from global wildfires to climate change. But the Permian detectives are faced with a host of suspects and not enough evidence to convict any of them.To understand this extinction, I wanted first to get a sense of its scale. That's difficult—sediments containing fossils from the end of the Permian are rare and often inaccessible. One site that preserves the extinction's victims lies about a half day's drive inland from Cape Town, South Africa, in a scrubland known as the Karoo."The Karoo is the kind of place where people fall asleep at the wheel," said Roger Smith, a paleontologist at the South African Museum, as we drove across the treeless land.
For every yard of altitude we gained, we traveled tens of thousands of years forward in time, heading for the Permian's conclusion.If we had driven here before the extinction, we would have seen animals as abundant and diverse as those of today's Serengeti, except most would have belonged to a group known as synapsids. Often called mammal-like reptiles—they looked like a cross between a dog and a lizard—the synapsids were Earth's first great dynasty of land vertebrates."We've found fossils of many kinds of synapsids in these rocks, especially tortoise-beaked dicynodonts, which likely lived in herds and browsed on vegetation along the riverbanks," said Smith.


They were preyed upon by gorgonopsians—fleet-footed synapsid carnivores with needle-sharp teeth."The late Permian rocks we passed as we neared Lootsberg Pass capture the synapsids at the height of their reign. For more than 60 million years they were Earth's dominant land vertebrates, occupying the same ecological niches as their successors, the dinosaurs.Smith slowed at a switchback, rolled down the window, and pointed to a horizontally banded cliff.
In the first few yards of the transition zone, only one or two Lystrosaurus fossils have been found scattered among all the diverse late Permian animals. Dozens of species of Permian synapsids disappear, leaving Lystrosaurus and a few others in early Triassic rocks. Animals were still abundant, but the community they formed was about as species rich as a cornfield.Plants were also hit by the extinction. I joined a research team led by Henk Visscher of the University of Utrecht at the Butterloch gorge, where exposed fossil beds cover the transition from the Permian to the Triassic. Sephton used his hammer to chip bits of rock from the layers that chronicle the extinction. The lower layers, dating from prior to the extinction, contain lots of pollen, typical of a healthy conifer forest. But in rocks from the Permo-Triassic boundary the pollen is replaced by strands of fossilized fungi—as many as a million segments in some golf-ball-size rocks.All that fungi in boundary rocks may represent an exploding population of scavengers feasting on an epic meal of dead trees.
As it decays, fungi grow into it from spores on the ground, decomposing it."Visscher and his colleagues have found elevated levels of fungal remains in Permo-Triassic rocks from all over the world. Bowring thinks the extinction took place in as little as 100,000 years—quicker than the click of a camera shutter on a geologic scale of time. Suspects must be capable of killing with staggering swiftness both on land and in the seas.
As I spoke with some of the researchers on the killer's trail, I learned how many suspects there are—and how difficult it is to develop a tight case.An enormous asteroid impact is the prime suspect of Gregory Retallack, a geologist at the University of Oregon.
They would have spread around the planet, then rained down on land and sea.Retallack has discovered tiny quartz crystals marked with microscopic fractures in rocks from the time of the extinction in Australia and Antarctica. After the clouds cleared, the atmosphere would be thick with carbon dioxide from fires and decaying matter. Herbivores would starve, as would the carnivores that fed on the plant-eaters.Other Permian detectives suspect the killer oozed up from the sea.
In 1996 English geologists Paul Wignall and Richard Twitchett of the University of Leeds reported the first evidence of oxygen depletion, or anoxia, in rocks that formed under shallow water at the time of the extinction.Pollution sometimes turns waters anoxic today in regions that lack good circulation.
Normally temperature differences between polar and equatorial waters create convective currents. Without those currents, anoxic water could have built up, spilling into shallow water as sea levels rose and smothering marine life.Permian oceans also might have been poisoned with CO2, according to Andrew Knoll, a paleobiologist at Harvard.


Dissolved bicarbonate was released as CO2, making the seas bubble at times like a glass of soda.The crisis for marine animals would have started when toxic levels of CO2 entered the shallows. Below the town of Norilsk lies a two-and-a-half-mile-thick (four-kilometer-thick) pile of lava, overgrown by conifers. Renne, an expert at determining the ages of rocks, has been trying to work out the timing of the events.
His lab is filled with machines—tangles of high-voltage cables, vacuum lines, and stainless steel—that date rocks by measuring the decay of radioactive isotopes within them. Renne secured chunks of lava from the Siberian Traps and Permo-Triassic boundary rocks from China. Renne doubts that's a coincidence.But the Siberian Traps volcanoes didn't cause the extinction by swamping the world with lava.
As volcanic gases poured into the skies, they would have generated acid rain, and sulfate molecules would have blocked sunlight and cooled the planet.
Sea level would have dropped, killing marine life in the shallows and severely reducing diversity.
Lowering sea level can also release the ocean's methane, which, combined with CO2 from the eruptions and decaying organic matter, would likely produce greenhouse conditions. Imagine a Laki erupting every year for hundreds of thousands of years."Each scientist I met left me thinking that he or she was a clue or two away from solving the crime.
But as Doug Erwin of the Smithsonian cautioned me, "the truth is sometimes untidy." The Permian extinction reminds him of Agatha Christie's Murder on the Orient Express, in which a corpse with 12 knife wounds is discovered on a train. A hundred million years from now?"I left Erwin's office at the Smithsonian and wandered into the dinosaur hall. Lystrosaurus, the synapsid that inherited the barren world of the Triassic, stared out empty-eyed. With its competition gone, Lystrosaurus spread across the world, from Russia to Antarctica.Death creates opportunity. I remembered the acid-tolerant plants of the Black Triangle, where we've done so much to destroy an ecosystem.



Emergency survival merit badge holders
Blackout movie 2013 online dublado


Comments to “National geographic article iceman”

  1. LADY writes:
    Sleep for the lake outdoors.
  2. Ayka012 writes:
    The identical bottle - and trade off.