From Wiki: About 66 million years ago, our planet experienced Cretaceous-Paleogene (K-Pg) it's fifth extinction event, a mass extinction which destroyed a majority of the world's Mesozoic species, including all dinosaurs except for birds. In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K-Pg boundary or K–T boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal iridium, which is more common in asteroids than in the Earth's crust. This is helpful for determining age in an excavation: below the K-Pg boundary-dinosaurs, above-none.
What caused this? Many scientists feel that a large meteorite hit Earth and radically changed the climate. The impact site is known as the Chicxulub crater.
It's been calculated that the meteorite was 6 miles in diameter. When it impacted creating an 150 mile wide crater, it threw a large amount of dust containing iridium into the atmosphere and literally dusted the entire planet creating this distinctive layer.
A minor extinction event happened roughly 12,900 years ago. The Younger Dryas or Mini Ice Age, temporary reversed the gradual warming of the planet after the Last Glacial Maximum. Although planet wide extinction of flora and fauna was not as extreme as the K-Pg event, the period of extreme cooling contributed to extinctions of more than 35 species of megafauna including giant sloths, sabre-tooth cats, mastodons and mammoths. It also impacted human populations. Africa seems to be one of the safest places and research has showed the greatest amount of species survival especially around Kenya.
What caused the Younger Dryas is controversial among scientists. One theory points to another celestial event as iridium is found in sediments from around this time.
One curious line of thought is that memories of this event became integrated into the oral history of surviving cultures. As a result, they became obsessive skywatchers for it had been told that oblivion had come from the sky. Perhaps priesthoods were created, eventually leading to worldwide astronomical calendars such as Newgrange, Stonehenge and the Pyramids.
One scary theory about where these meteors come from points to the annual Taurid meteor shower that occur each Fall and cluster of debris known as the Taurid Resonant Swarm. As you can see by this map, Earth's orbit crosses the Taurid path twice during the year.
The 1908 Tunguska, Russia event is thought to be linked to the Taurid debris. A meteor air burst of 3-50 megatons flattened an estimated 80 million trees over an area of 830 sq mi. Fortunately, this happened in Siberia where human population is sparse. This explosion over an urban area would have been catastrophic. And what was found at the site? Iridium!
Within the scientific community, there are those quite concerned about another large object from the Taurid orbit hitting Earth as depicted in:
As if we don't have enough to worry about!
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