Nov 7, 2016

Fossilized Leaves Reveal How Earth Recovered After Mass Extinction

Recreation of an asteroid hitting Earth.
About 66 million years ago, an asteroid slammed into Earth, causing a mass extinction event that wiped out the dinosaurs. What happened in the years following the devastation has long been a mystery due to lack of evidence.

Now researchers have discovered clues thanks to a surprising find: insect damage to plants now fossilized in rock. The damage suggests that half of Earth recovered twice as fast as the other half.

"We compared insect damage diversity in Patagonia and Western Interior North America before and after the asteroid impact," lead researcher Michael Donovan of Pennsylvania State University explained to Seeker. "In both Patagonia and North America, we observed a decrease in insect damage diversity on fossil leaves that lived in the early Paleocene, after the asteroid hit Earth."

"However," he added, "in Patagonia, insect damage diversity increased to pre-extinction levels in 4 million years, much faster than the 9 million years it took in North America." Donovan and his team reported their findings in the journal Nature Ecology & Evolution.

Insect damage, including multiple small leaf mines (upper right) and margin feeding (upper left), on a fossil leaf from an early Paleocene fossil plant locality, Las Flores (~62.3 million years old), in Patagonia, Argentina.
Other researchers have proposed that after the asteroid smashed into Earth near what is now Chicxulub, Mexico, the planet saw increased volcanic activity and severe climate change. Those events have been implicated in wiping out all dinosaurs that didn't evolve into birds, as well as numerous other plants, insects and animals on land and in the seas.

The fossilized leaves of flowering plants suggest that just before the destruction happened, a wide range of insects at various places on the planet were happily munching away on plants. Shortly after the asteroid hit, this feeding activity stopped. When the researchers focused only on leaf miners — numerous insects, such as moths and flies, whose larvae burrow into and feed on leaves — the evidence for annihilation was incredibly stark.

"We found no evidence for the survival of any of the Cretaceous leaf miners in Patagonia, similar to previous findings from North America," Donovan said.

Insect galls on a fossil leaf from the latest Cretaceous Lefipán Formation (67-66 million years old) in Patagonia, Argentina.
Some leaf miners must have survived elsewhere, though, since these insects live on to this day. Birds, the early ancestors of mammals, certain fish and other species also managed to survive, becoming more established as the years went on. The recovery, at least for insects and flowering plants, happened over twice as fast in the Southern Hemisphere as it did the Northern Hemisphere.

As for why, Donovan said, "One possibility is distance from the Chicxulub crater in Mexico." He thinks that other "poorly understood factors may have also contributed" to the major difference in recovery times.

Read more at Discovery News

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