The rocks that surrounded us date from the late Permian. 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. 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. Brace yourself, you're about to go through the extinction.
A synapsid known as Lystrosaurus appears in these sediments. Smith had a skull of the animal in his truck. Its flat face gave it the look of a bulldog with tusks. 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.
Higher up, the diversity suddenly dwindles. 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. Evidence for the scale of damage to the world's forests comes from the Italian Alps.
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. The beds lie high on a cliff, accessible only by climbing piles of debris. I anxiously followed veteran climber Mark Sephton up a slope of loose rocks to a ledge. Sephton used his hammer to chip bits of rock from the layers that chronicle the extinction.
Each fragment contains microscopic fossils—pieces of plants and fungi. 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. They call it a "fungal spike. Visscher's conclusion: Nearly all the world's trees died en masse. On the drive from Butterloch, a team member handed me a soft, brown banana—a leftover from lunch.
Bowring thinks the extinction took place in as little as , 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. The collision would have sent billions of particles into the atmosphere , he explains.
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.
I asked Retallack what an impact would be like if we had been standing a few hundred miles from ground zero. Temperatures would drop, and corrosive acid snow and rain would fall. After the clouds cleared, the atmosphere would be thick with carbon dioxide from fires and decaying matter.
CO2 is a greenhouse gas; it would have contributed to global warming that lasted millions of years. The short-term effects alone—cold, darkness, and acid rain—would kill plants and photosynthetic plankton, the base of most food chains. Herbivores would starve, as would the carnivores that fed on the plant-eaters.
Other Permian detectives suspect the killer oozed up from the sea. For years scientists have known that the deep ocean lacked oxygen in the late Permian. Kies je bindwijze. Direct beschikbaar. Verkoop door bol. When Life Nearly Died. E-book is direct beschikbaar na aankoop E-books lezen is voordelig Dag en nacht klantenservice Veilig betalen.
Anderen bekeken ook. Life After Loss. Is There Life After Death? Life After Death. What's after Life? Death on Earth. Life after Death. Nine Lives A Journey through Life.
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