October 23, 2017

13.04.10- Mammoth Extinction vs. Impact Theory.

Woolly Mammoths: hunted to extinction?

  

   An Ice Age extinction mystery has just got more complicated. North America used to be home to some amazing mega-animal life, including wooly mammoths, saber-toothed cats the size of grizzly bears, and armadillos the size of Volkswagens. Then, around the time period known as the Younger Dryas about 12,900 years ago, a mass continent-wide extinction event occurred. Key theories include massive climate change, a large cometary impact, and that greatest of all predators, man. Now, research by Jacuelyn Gill of the University of Wisconsin has dealt a blow (pun intended) to the cometary impact hypothesis. Key evidence for a large airburst over the Laurentide ice sheet comes in the form of an iridium layer seen in the sedimentary deposits laid down at the time, as well as the discovery of minuscule nano-diamonds generated by the heat and blast of the explosion. The problem is, Gill’s studies of fungus spores found in fossilized dung finds the extinction event was already underway well before the impact, around 14,000 years ago. In addition, a mastodon skeleton in the Cincinnati museum has been found to have been dated from circa 10,055 years ago, well after the impact! This seems to put the appearance of Clovis man and overhunting as the key to large mammal extinction in the Ice Age North American scene. Perhaps even a combination of the factors was the cause. The concept of the Early Dryas extinction is unique because it is the most recent extinction event (other than the one we’re currently undergoing!) along a timeline of multiple events throughout the history of life on Earth. Being the most recent, perhaps more evidence for complicating factors is simply lying around for us to find. This debate is thus the hottest topic of all large extinction events. And one has to wonder; what would life in modern U.S. suburbia and camping trips be like if there were still saber-toothed cats around?

08.11.09:Does Cometary Mass Extinction Need to be Rewritten?

Comets are cause all mass extinctions in Earth’s history, right? Maybe not, if new research is correct. Simulations run by the scientists at the University of Washington now suggest that the giant planets of Jupiter and Saturn may do a much more through job of cleaning up incoming debris than is generally realized. Short period comets such as Halley’s are generally accepted to be denizens of the Kuiper belt, which extends out to 100 Astronomical Units (A.U.s), while much more numerous populations of long period comets are theorized to come from the Oort cloud, a massive solar system-engulfing sphere at a distance of 1,000 A.U. to up to 3 light years distant. Traditional cometary mass extinction theory states that when a star passes close enough to the shell of the Oort cloud, a rain of comets are pried free and the inner solar system becomes a celestial shooting gallery for a million years or so. Simulations, however, suggest no more than three impacts could have occurred over the last 500 million years or so, fuel for at best maybe a minor extinction event or two. Then there’s the pesky affair of some extinct species shown to exist above the K-T iridium layer… doubtless, the case of mass extinction is a thoroughly messy business. As reported earlier last month in this space, more than one impactor is suspected in the extinction of the dinosaurs. Examination of other inner solar system bodies should pin down the frequency, duration, and average number of killer comets, as the Moon, Mars and even Mercury have relatively little erosion and would be potential targets as well. Any incoming comet stands a 40% chance of having its orbit altered by Jupiter, as happened to Hale-Bopp in the late 90′s. Thanks, Jove!

 

 

 

04.11.09:Did Ancient Comets give Earth its Seas?

Comets continue to be at the center of controversy concerning the early Earth and life. If you’ve been following our recent reports as of late, you know that opinions run the gamut, from ancient cometary impacts being relatively rare, to comets being crucial to life as we known it. Now, researchers at the Niels Bohr Institute in Denmark have scored one for the comet camp. Recent studies of ancient rocks in Greenland suggest that the primordial Earth may have undergone a massive cometary bombardment early in its history, about 3.85 billion years ago. Were talking waaaaay back in the Archean period, before life had even taken hold. The conclusion is based on our friendly elemental smoking gun, Iridium. Rare on Earth, what little iridium is found in the Earth’s crust is almost certainly of extraterrestrial origin. Asteroid impacts generally distribute about 18,000 parts per trillion, while comets, due to a higher impact velocity and icy rock composition, produce amounts much lower, about 130 parts per trillion. The team found a ratio of 150 ppt, strongly suggesting that comets were the primary constituents of the Late Heavy Bombardment. This is a tantalizing clue in two enduring mysteries concerning the early Earth; how did we our get our large oceans, and how did life start? Looking out into the solar system, we are the only planet with a large surface covering of liquid water. Could it have been deposited by comets? That’s a lot of dirty snowballs… there is some thought that life itself, or at least amino acids, known as the chemical building blocks of life, might have been deposited in the same fashion by a method known as panspermia. Not all scientists remain convinced, however, and for now, spinning cometary hypotheses remains a sure way to generate scientific controversy. Are we all “comet-stuff?”

 

27.10.09: Exploring Shiva Crater.

Move over, Chicxulub; we may have a new contender in the realm of cosmic extinction events. Recently, paleontologist Sankar Chatterjee of Texas Tech University has dubbed a ring shaped subsurface structure off of the western coast of India Shiva crater. If Chaterjee is correct, it would be one of the largest impact basins on Earth recorded, at a diameter of about 500 km wide. Aptly named after the Hindu goddess of destruction, Shiva would have been caused by an asteroid or comet of about 40 km in diameter. Chaterjee has been following data accrued by decades of off-shore oil drilling projects in the area; the existence of iridium deposits suggests a calamity of cosmic origin. Rare on Earth but common on asteroids, the element iridium was considered a “smoking gun” in dating the aforementioned K-T extinction event of about 65 million years ago. Tantalizingly, the Shiva Crater event also seems to date from the same era. This raises the question; could a hail of cometary debris have been common in that far gone time? Bodies without rapid erosion, such as our Moon or Mars, should show evidence of impacts dating from around this epoch. Of course, the crater hypothesis is not without its critics…the area surrounding the Indian subcontinent is very geologically active as it pushes under the plates of the Asian continent. In particular, an area known as the Deccan Traps extends to the edge of Shiva and was very active during the Cretaceous period. Also, Shiva appears to have rock from the Earth’s underlining mantle exposed, again tantalizing evidence for a past cataclysm… this area of our own near space begs for further exploration!