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
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When a six mile-wide asteroid struck the Earth 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, including the non-avian dinosaurs like Tyrannosaurus, the flying pterosaurs, the coil-shelled squid cousins called ammonites and 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 from the devastation.
 
In a new Earth and Planetary Science Letters paper, Smithsonian's Kirk Johnson, director of the National Museum of Natural History, geologist William Clyde of the University of New Hampshire 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 enough ash 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. When 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. Using a technique known as uranium-lead dating, the geologists 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 or the sweltering rainforests that came after. Fossil pollen records show that there was what paleontologists refer to as a "fern spike."  That was 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. Not only was the mass extinction 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, catastrophic and widespread," Miller says.
 
Studies like these are offering ever-greater resolution of scenes from the deep past.
 
"Geochronology is getter better and more precise all the time. And this study applies it to a unique outcrop that is unparalleled in its ash bed sequence," Johnson says. He adds that studying such patterns isn't just ancient history. "The K/Pg was both instant and global. So it is a very interesting analogy for the industrial Anthropocene of the last century," Johnson says.
 
By studying the past, we may catch a glimpse of the future we're creating.

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CRITICAL THINKING QUESTION
How do we know that a six mile-wide asteroid struck the Earth 66 million years ago?
Write your answers in the comments section below


COMMENTS (13)
  • olivial-orv
    10/05/2016 - 04:52 p.m.

    Wow, this study shows that the death of dinosaurs was the birth of Mammals. Without this asteroid, maybe humans would'nt even exist.

  • sebastianj-ver
    10/07/2016 - 10:20 a.m.

    Maybe people were bigger then we are back then

  • jackiek-orv
    10/11/2016 - 01:00 p.m.

    Because how else woud 75% of species die out.

  • braydenm-lew
    10/11/2016 - 03:32 p.m.

    The asteroid was quite a collision, but life continued very quickly after.

  • cassidys-sto
    10/13/2016 - 11:44 a.m.

    All the dinosaurs died.

  • dakotaw-sto
    10/13/2016 - 11:50 a.m.

    We have seen the crater that the asteroid left on earth.
    We have also seen that asteroid can come into our solor system.

  • kalebk1-sto
    10/13/2016 - 11:52 a.m.

    We know because it killed all the dinosaurs on the earth 66 million years ago when all the dinosaurs died.

  • hectors-cas
    10/17/2016 - 05:05 p.m.

    The dates and fossils speak to how dramatically the extinction changed the plant.Not only was the mass extinction 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.

  • cbrooke-dav
    10/19/2016 - 08:23 p.m.

    In response to "Life bounced back after the dinosaurs died," I would say that this is a big scientific discovery. One reason I would say is because "It helps put a timer on how quickly life bounced back from the devastation." Another reason is that "By studying the past, we may catch a glimpse of the future we're creating." It says in the article that "These rocks provide a more precise timing for what's seen in the fossil record.". Even though we don't now to much about that time period, I think that this discovery could help us better understand that.

  • larno-wim
    10/21/2016 - 11:35 a.m.

    When a 6-mile long asteroid hit earth around 4million years ago, it destroyed most of the earth and animals. However, it did not kill all species. If it killed all of the species, that means there would be no mammals alive even to this day. That means there would be no humans alive which means there would be no you.

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