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Sioux Falls Scientists endorse Day the Dinosaurs Died for describing the
details of how an asteroid impact caused the extinction of the
Dinosaurs and made room for the evolution of mammals.

Day the Dinosaurs Died

Day the Dinosaurs Died (2018) - 60 minutes
Day the Dinosaurs Died at Amazon.com

66 million years ago, a seven-mile-wide asteroid collided with Earth, triggering a chain of events suspected of ending the dinosaurs' reign. But experts have long debated exactly what happened when the asteroid struck and how the giant beasts met their end. Now, scientists have uncovered compelling new clues about the catastrophe - from New Jersey to the wilds of Patagonia, and an international expedition of scientists has drilled into the impact crater off the coast of Mexico, recovering crucial direct evidence of the searing energy and giant tsunami unleashed by the asteroid. Join NOVA as scientists piece together a chillingly precise unfolding of the Earth's biggest cataclysm, moment by moment. And discover how our early mammalian ancestors managed to survive and repopulate the Earth.

4-10-19 The very strong case for an asteroid defense system
No, really — this is serious. limate change is a serious threat to human society. But even the most extreme worst-case future scenario wouldn't wipe out humanity instantly. There's only one thing that might do that — a major asteroid or comet impact. Big asteroid strikes are very rare, of course, but if one were to come along, we would all be dead in a matter of months — and while a small one wouldn't be so bad, it could still cause devastating losses. It sounds a bit silly, but there is a very strong case for the American government to set up a planetary asteroid defense system. It wouldn't cost much — just a few satellites and telescopes to keep track of all potential threats, and developing some collision or gravity-based techniques to deflect them if necessary. The New Yorker recently published a fascinating profile of a paleontologist named Robert DePalma who has discovered what appears to be fossils of animals who died in the Cretaceous-Paleogene extinction event. It has been widely accepted that a big asteroid impact in Mexico probably caused the extinction, but until DePalma's discoveries in the Hell Creek Formation in North Dakota, nobody had found dinosaur fossils very close to the Cretaceous-Paleogene geological boundary layer (suggesting that perhaps they died out earlier than the impact). If DePalma is right, it will be a landmark finding for the field. Pretty cool science! But the article also has a harrowing description of what happened when the Chicxulub impactor (a comet or asteroid, perhaps 11-81 kilometers wide) smashed into the Yucatan Peninsula 66 million years ago, creating a crater 93 miles in diameter. First came fire, as the kinetic energy released by the impact scorched everything in a 1,500-mile radius, and red-hot ejecta landed all around the world. Continent-wide firestorms burned up about 70 percent of all the world's forests, and huge tsunamis tore up the Gulf of Mexico. Then it got a lot worse: The dust and soot from the impact and the conflagrations prevented all sunlight from reaching the planet’s surface for months. Photosynthesis all but stopped, killing most of the plant life, extinguishing the phytoplankton in the oceans, and causing the amount of oxygen in the atmosphere to plummet. After the fires died down, Earth plunged into a period of cold, perhaps even a deep freeze. Earth’s two essential food chains, in the sea and on land, collapsed. About 75 percent of all species went extinct. More than 99.9999 per cent of all living organisms on Earth died, and the carbon cycle came to a halt. Big land animals fared particularly poorly — virtually everything weighing more than 5 kilograms was wiped out. Mammals at that time were mostly small, so the ones that survived were able to evolve into larger species after the ecosystem began to recover. In the history of our planet, that's almost as bad as it gets (only the Permian-Triassic extinction was worse). But it's worth noting that even a small asteroid can cause enormous damage. In 2013, one only about 66-feet wide exploded in the sky near Chelyabinsk Oblast in Russia, shattering windows across the city and causing about 1,500 injuries. The explosion was as powerful as a large nuclear weapon — a direct hit on a major city would have killed millions. So what do we do? The first thing is to track and record all the near-Earth objects, which is already underway with many projects across the globe and in space. Years ago, Congress required NASA to track 90 percent of objects one kilometer and over, which was accomplished as of 2011 — but smaller ones are still being racked up by the thousands. All told, nearly 20,000 near-Earth objects have been found at time of writing. Meanwhile, NASA's Jet Propulsion Laboratory has an automated system to detect which objects are a threat.

3-29-19 Chicxulub asteroid impact: Stunning fossils record dinosaurs' demise
Scientists have found an extraordinary snapshot of the fallout from the asteroid impact that wiped out the dinosaurs 66 million years ago. Excavations in North Dakota reveal fossils of fish and trees that were sprayed with rocky, glassy fragments that fell from the sky. The deposits show evidence also of having been swamped with water - the consequence of the colossal sea surge that was generated by the impact. The detail is reported in PNAS journal. Robert DePalma, from the University of Kansas, and colleagues say the dig site, at a place called Tanis, gives an amazing glimpse into events that probably occurred perhaps only tens of minutes to a couple of hours after the giant asteroid hit the Earth. When this 12km-wide object slammed into what is now the Gulf of Mexico, it would have hurled billions of tonnes of molten and vaporised rock into the sky in all directions - and across thousands of kilometres. And at Tanis, the fossils record the moment this bead-sized material fell back down and strafed everything in its path. Fish are found with the impact-induced debris embedded in their gills. They would have breathed in the fragments that filled the water around them. There are also particles caught in amber, which is the preserved remnant of tree resin. It is even possible to discern the wake left by these tiny, glassy tektites, to use the technical term, as they entered the resin. Geochemists have managed to link the fallout material directly to the so-called Chicxulub impact site in the Gulf. They have also dated the debris to 65.76 million years ago, which is in very good agreement with the timing for the event worked out from evidence at other sites around the world. From the way the Tanis deposits are arranged, the scientists can see that the area was hit by a massive surge of water. Although the impact is understood to have generated a huge tsunami, it would have taken many hours for this wave to travel the 3,000km from the Gulf to North Dakota, despite the likely presence back then of a seaway cutting directly across the American landmass. Instead, the researchers believe local water could have been displaced much more quickly by the seismic shockwave - equivalent to a Magnitude 10 or 11 earthquake - that would have rippled around the Earth. It is a type of surge described as a seiche, which would have picked up everything in its path and dumped it into the jumbled collection of specimens now being reported by the team. "A tangled mass of freshwater fish, terrestrial vertebrates, trees, branches, logs, marine ammonites and other marine creatures was all packed into this layer by the inland-directed surge," said Mr DePalma. "A tsunami would have taken at least 17 or more hours to reach the site from the crater, but seismic waves - and a subsequent surge - would have reached it in tens of minutes," he added.

12-18-18 Erosion has erased most of Earth’s impact craters. Here are the survivors
A recent discovery in Greenland may bring the known list to 191. When it comes to impact craters, Earth is the pauper of the solar system. Even with a recent, still-to-be-confirmed crater discovery under Greenland’s ice, there are fewer than 200 known impact craters on the planet. Mars, for comparison, has hundreds of thousands. Produced by falling space rocks, most impact craters on Earth have been wiped away over time by wind, rain, shifting ice and the crawl of tectonic plates. Here are the 190 confirmed survivors, as recorded in the Earth Impact Database, maintained by the University of New Brunswick in Canada — plus the newcomer in Greenland. Identifying and studying such features could give scientists clues about the history of Earth, including the evolution of life itself. Researchers have tried to link various craters to the five known mass extinctions, for example. But only the space rock that created Chicxulub, hidden under Mexico’s Yucatán Peninsula and the Gulf of Mexico, is widely accepted as causing a major die-off. That space rock left a crater 150 kilometers wide and may have done in the dinosaurs and many other creatures about 66 million years ago (SN: 2/4/17, p. 16). Popigai, in Siberia, which measures about 90 kilometers from rim to rim, might be connected to a smaller die-off of mostly marine creatures about 34 million years ago. But that’s far from settled. Chicxulub and Popigai are the largest craters dating to the last 100 million years. But the roughly 160-kilometer-wide Vredefort crater in South Africa edges out Chicxulub as the largest known ever. Estimates put Vredefort’s origin around 2 billion years ago, making it the oldest known impact crater too.

10-25-18 Splosh! How the dinosaur-killing asteroid made Chicxulub crater
It is hard to imagine billions of tonnes of rock suddenly start to splosh about like a liquid - but that is what happened when an asteroid struck the Earth 66 million years ago. Scientists have now put together a detailed picture of the minutes following the giant impact. This, remember, is the colossal event that wiped out the dinosaurs. The analysis of rocks drilled in 2016 from the leftover crater show they underwent a process of fluidisation. The pulverised material literally began to behave as if it were a substance like water. Models had predicted what should happen when a 12km-wide stony object from space punched the ground. Initially, a near-instantaneous bowl would have been created some 30km deep and up to 100km wide. Then, instabilities would have seen the sides collapse inwards and the base of the hole rebound skyward, briefly reaching higher than the Himalayas. When everything had settled down, a crater roughly 200km wide and 1km deep would remain. This is the feature that is now buried under sediments in the Gulf of Mexico, close to the port of Chicxulub. The impact description - scientists call it the dynamic collapse model of crater formation - is only possible if the hammered rocks can, for a short period, lose their strength and flow in a frictionless way. And it is the evidence for this fluidisation process that researchers now report after studying the rocks they drilled from something called the "peak ring" - essentially, a circle of hills in the centre of the remnant Chicxulub depression. "What we found in the drill core is that the rock got fragmented. It was smashed to tiny little pieces that initially are millimetre sized; and that basically causes this fluid-like behaviour that produces in the end the flat crater floor, which characterises Chicxulub and all such large impact structures, including those we also see on the Moon," explains Prof Ulrich Riller, from the University of Hamburg, Germany.

Day the Dinosaurs Died

Sioux Falls Scientists endorse Day the Dinosaurs Died for describing the
details of how an asteroid impact caused the extinction of the
Dinosaurs and made room for the evolution of mammals.