Life bounced back after the dinosaurs died
Kirk Johnson at work at the Bowring Pit in the Denver Basin, where his research team studied the sedimentary rock site. (Rick Wicker/iStock/estt)
Life bounced back after the dinosaurs died
September 30, 2016
Published: September 30, 2016
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A six mile-wide asteroid once struck the Earth. That was 66 million years ago. It was one of the worst days in the history of the planet. About 75 percent of the known species were rapidly driven to extinction. These included dinosaurs like Tyrannosaurus. But there were many more.
Life was not totally extinguished, however. The close of the Age of Dinosaurs opened up the path to the Age of Mammals.
Now a new study has been done. It helps put a timer on how quickly life bounced back.
A new Earth and Planetary Science Letters paper has been produced. One of the scientists is Smithsonian's Kirk Johnson. He is director of the National Museum of Natural History. Another scientist is geologist William Clyde of the University of New Hampshire. They and their coauthors draw from the fossil and rock record of the Denver Basin. They try to determine what happened after the devastating asteroid impact. The region is located in eastern Colorado. It extends into Wyoming and Nebraska. The region is one of the best places in the world to examine the change.
"The Denver Basin was actively subsiding. And the adjacent Colorado Front Range was actively uplifting during the last four million years of the Paleocene," Johnson says. It means, "the basin was acting like a tape recorder of local events." Better still, he says, nearby volcanic eruptions spewed plenty of ash. It was enough that geologists now have hundreds of layers that can be given absolute dates to determine the age of these rocks.
These rocks provide a more precise timing for what's seen in the fossil record.
The change between the Late Cretaceous and the subsequent Paleogene period is stark.
"The Late Cretaceous was forested and warm," Johnson says. Forests were dominated by broadleaf trees, palms and relatives of ginger. Then the extinction struck. It stripped away the big herbivorous dinosaurs. And, says paleobotanist Ian Miller of the Denver Museum of Nature & Science, it killed about 50 percent of plant species. The surviving species created a new landscape.
"Within two million years of the impact, the Denver Basin had the world's first known tropical rainforests. And mammals of medium body size," says Johnson.
The study focuses on what happened between those points. The scientists used a technique known as uranium-lead dating. They determined that the K/Pg boundary (the layer that records the asteroid strike and marks the divide between the Cretaceous and subsequent Paleogene period) was 66.021 million years ago.
Johnson and colleagues estimate that the time between the last known non-avian dinosaurs and the earliest Cenozoic mammal was about 185,000 years. They say it was no more than 570,000 years. That's just a blip from the perspective of Deep Time. That's the incomprehensible span of ages. It is where the whole of human history is just a footnote.
The landscape during this transition didn't resemble the Cretaceous forests. Nor did it resemble the sweltering rainforests that came after. Fossil pollen records show that there was what paleontologists refer to as a "fern spike." This is when these low-growing plants proliferated over the landscape. It lasted about 1,000 years. That's because ferns thrive after disturbances, Miller says. "They just need a little bit of substrate and water and they are off."
The dates and fossils speak to how dramatically the extinction changed the planet. The mass extinction was extremely rapid. But life recovered relatively quickly as well. There was less than half a million years between the likes of Triceratops and the time when the surviving mammals started to take over the basin's recovering ecosystems.
"The new paper really drives home the point that the extinction was, from a geological standpoint, immediate." It was catastrophic and widespread, Miller says.
Studies like these are offering ever-greater resolution of scenes from the deep past. And by studying the past, we may catch a glimpse of the future we're creating.
Source URL: https://www.tweentribune.com/article/junior/life-bounced-back-after-dinosaurs-died/
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CRITICAL THINKING QUESTION
How do we know that a six mile-wide asteroid struck the Earth 66 million years ago?
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