Winston
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Last day of the dinosaurs' reign captured in stunning detail
Rocks from deep inside the Chicxulub impact crater show what happened in the minutes to hours after one of our planet’s most catastrophic events.
9 Sep 2019
https://www.nationalgeographic.com/...day-dinosaurs-reign-captured-stunning-detail/
Previous studies have been slowly piecing together what happened after the so-called Chicxulub impact using a combination of computer models and the geologic fallout found at a smattering of sites around the world. One controversial locale in North Dakota may even capture an entire ecosystem catastrophically tossed by the seismic waves that rippled out from the impact zone.
But the exact details of the chaos that ensued have been an enduring mystery, one that scientists hoped to solve by closely examining the impact crater itself. Layers of sediment had buried the crater over millennia, which prevented roaring winds and water from wearing it away, but also hid it out of reach of eager scientists. To actually touch this infamous moment in our planet’s history, researchers needed to drill.
Scientists started exploring the crater’s structure in 1996 via seismic surveys led by Joanna Morgan, who co-led the latest drilling efforts with Gulick. Along with a second expedition in 2005, that work confirmed the presence of what’s known as a peak ring—a circle of buried mountains that rapidly forms within the largest of impact craters. Such a structure is an ideal place to drill, Gulick says. Not only can it reveal the fundamental processes behind the formation of mega-craters, its elevation places it relatively close to the modern ocean floor, which means easier access.
In the spring of 2016, the team at last sunk metal teeth into the Chicxulub crater, and over the course of two months, they extracted sections of core 10 feet at a time. In total, they collected a slice of Earth about a half-mile long that captures the shocked rocks that were below the impact, layers of melted rock, and the transition back to normal seafloor sediments.
The new study of that core sample combines the rocky record with computer models to create an unprecedented timeline of the geologic chaos on the day sparking the dinosaurs' demise.
“To say that we’re looking at something that happened the day the impact happened 66 million years ago, that’s a kind of resolution that we almost never see in geology,” Anderson says.
One of the most striking finds is the rate at which material was re-deposited after the impact. The asteroid strike excavated miles of ocean floor, vaporizing rock and water in a flash. A ripple of shockwaves inside the crater sent solid rock flowing like liquid to form a towering peak, which then collapsed outward to form the peak ring. Just tens of minutes later, a jumble of debris piled onto the peak ring in a layer some 130 feet thick. Some of this material came from a sheet of melted rock that splashed into place within minutes as the peak collapsed.
Then, as the ocean rushed back into the yawning molten gap, pockets of steam burst forth, flinging up more fragments of rock. Within an hour, the crater was likely covered in a churning vat of rocky oceanic soup, periodically sloshed by the collapse of the crater’s steep wall.
“Just like if you pour a bucket of water into a bathtub, it doesn’t sit quiet, it sloshes around,” Melosh explains. “Each slosh as it went back and forth deposited more material.”
Rocky bits slowly settled out from the stew, piling up hundreds of feet of more debris. In total, the event laid down nearly 430 feet of new material in a single day.
What’s more, the rock core offers clues to how the collision instantly affected life on land. Hurtling to Earth at some 45,000 miles an hour, the impact likely sent out a flash of energy that ignited landscapes within a 900 miles radius.
“Mexico was on fire immediately,” Anderson says. The impact also flung geologic shrapnel high into the skies that plummeted back around the globe, igniting fires even farther from the impact zone. And in the top few inches of the core’s sediment, the scientists found bits of charcoal, likely created by those raging wildfires.
A piece of the asteroid that killed the dinosaurs:
Rocks from deep inside the Chicxulub impact crater show what happened in the minutes to hours after one of our planet’s most catastrophic events.
9 Sep 2019
https://www.nationalgeographic.com/...day-dinosaurs-reign-captured-stunning-detail/
Previous studies have been slowly piecing together what happened after the so-called Chicxulub impact using a combination of computer models and the geologic fallout found at a smattering of sites around the world. One controversial locale in North Dakota may even capture an entire ecosystem catastrophically tossed by the seismic waves that rippled out from the impact zone.
But the exact details of the chaos that ensued have been an enduring mystery, one that scientists hoped to solve by closely examining the impact crater itself. Layers of sediment had buried the crater over millennia, which prevented roaring winds and water from wearing it away, but also hid it out of reach of eager scientists. To actually touch this infamous moment in our planet’s history, researchers needed to drill.
Scientists started exploring the crater’s structure in 1996 via seismic surveys led by Joanna Morgan, who co-led the latest drilling efforts with Gulick. Along with a second expedition in 2005, that work confirmed the presence of what’s known as a peak ring—a circle of buried mountains that rapidly forms within the largest of impact craters. Such a structure is an ideal place to drill, Gulick says. Not only can it reveal the fundamental processes behind the formation of mega-craters, its elevation places it relatively close to the modern ocean floor, which means easier access.
In the spring of 2016, the team at last sunk metal teeth into the Chicxulub crater, and over the course of two months, they extracted sections of core 10 feet at a time. In total, they collected a slice of Earth about a half-mile long that captures the shocked rocks that were below the impact, layers of melted rock, and the transition back to normal seafloor sediments.
The new study of that core sample combines the rocky record with computer models to create an unprecedented timeline of the geologic chaos on the day sparking the dinosaurs' demise.
“To say that we’re looking at something that happened the day the impact happened 66 million years ago, that’s a kind of resolution that we almost never see in geology,” Anderson says.
One of the most striking finds is the rate at which material was re-deposited after the impact. The asteroid strike excavated miles of ocean floor, vaporizing rock and water in a flash. A ripple of shockwaves inside the crater sent solid rock flowing like liquid to form a towering peak, which then collapsed outward to form the peak ring. Just tens of minutes later, a jumble of debris piled onto the peak ring in a layer some 130 feet thick. Some of this material came from a sheet of melted rock that splashed into place within minutes as the peak collapsed.
Then, as the ocean rushed back into the yawning molten gap, pockets of steam burst forth, flinging up more fragments of rock. Within an hour, the crater was likely covered in a churning vat of rocky oceanic soup, periodically sloshed by the collapse of the crater’s steep wall.
“Just like if you pour a bucket of water into a bathtub, it doesn’t sit quiet, it sloshes around,” Melosh explains. “Each slosh as it went back and forth deposited more material.”
Rocky bits slowly settled out from the stew, piling up hundreds of feet of more debris. In total, the event laid down nearly 430 feet of new material in a single day.
What’s more, the rock core offers clues to how the collision instantly affected life on land. Hurtling to Earth at some 45,000 miles an hour, the impact likely sent out a flash of energy that ignited landscapes within a 900 miles radius.
“Mexico was on fire immediately,” Anderson says. The impact also flung geologic shrapnel high into the skies that plummeted back around the globe, igniting fires even farther from the impact zone. And in the top few inches of the core’s sediment, the scientists found bits of charcoal, likely created by those raging wildfires.
A piece of the asteroid that killed the dinosaurs:
