Thursday, February 21, 2013

Asteroids & Extinctions

Asteroid 2012 DA14 flyby Feburary 15, 2013

   My three favorite novels written by the late scientist and science fiction author, Sir Arthur C Clark (who is probably most famous for working out how geosynchronous satellites would work (those that stay in the same position over the planet's surface), and his collaboration with film director Stanley Kubrick on "2001, a Space Odyssey"), are these; "The Fountains of Paradise," which concerns a elevator that reaches into space, "Childhood's End," which concerns the final evolution of mankind, and my favorite, "Rendezvous With Rama," which is about our first contact with extraterrestrials, or at least their artifacts. 
   The novel begins quite smashingly with a thousand ton meteorite crashing through the Earth's atmosphere at 31 miles per second, and hitting the planets surface, completely destroying the northern Italian cities of Padua and Verona in the year of 2077.
   According to Clark this event was totally unexpected, and resulted in the creation of SPACEGUARD, which was a program designed to track objects in the solar system, which may or may not come near our planet. And this resulted in the detection of Rama, the great 25 mile long cylindrical spacecraft which was visiting our solar system, and which concerned the remainder of the book.
   It now seems odd that mankind would not have taken such efforts so far in our future, for we now have a program that searches for Near-Earth Objects (NEO), which is also called Spaceguard, the term coined from Sir Arthur's novel, in anticipation of the very circumstance described above.
   "A 1992 US Congressional study produced a "Spaceguard Survey Report"  which led to a mandate that NASA locate 90% of near-Earth asteroids larger than 1 km within 10 years." -Wikipedia
   It seems we are more far sighted than the Earth's civilization of Clark's imagination. Or it's possible that his vision warned us to get into action. For that we would owe him a great deal.
   The solar system was literally filled with objects floating around during it's early history. Our very own Moon was formed when a Mars sized object collided into the Earth shortly after it formed about 4.57 billion years ago. If you look at it now it's easy to see the scars of impact craters. The reason the Earth doesn't look like the Moon is due to the fact that it has an atmosphere which allows the erosion process to erase the evidence of thousands (or more) of it's own impacts. Still, the Meteor Crater near Flagstaff Arizona is proof of our planet's violent history, and that it is literally a target for future collisions.
   The Spaceguard Survey met it's mandated goal, although taking a little longer than 10 years. Still it has had it's exceptions. On June 6th of 2002, an undetected meteor exploded over the Mediterranean Sea with the force of a small atomic bomb. In September of the same year it is thought that a meteorite, or comet nucleus, impacted the Earth near the Vitim River Basin in Russia (It seems that Russia has had more than it's fair share of these type of events). And so on.
   Still the Spaceguard program has been successful in identifying many NEOs, and is much better than having no Spaceguard program at all. 
   The asteroid (asteroids are small solar system bodies or dwarf planets that are not comets (of course there is no reason comets can't smash into us as well). Meteors are small bodies of matter from outer space that enters the earth's atmosphere, appearing as a streaks of light (these are what we sometimes call Shooting Stars). The term meteoroid is synonymous with meteor. A meteorite is a meteoroid that survives impact with the Earth's surface. 100,000 tons of meteorite material reach the Earth's surface every year) 2012 DA14 was detected by astronomers in Spain on February 23, 2012. It's dimensions were calculated to be approximately 98 feet in diameter, with a mass of  40,000 metric tons. Astronomers examined it's orbit and discovered that it would come within 17,200 miles from the surface of Earth on Feburary 15, 2013, and indeed it did. This is a record close approach for a known object of this size (it came closer to the planet's surface than the satellite that transmitted the broadcast signal for the last Superbowl). Had it hit the Earth it would have resulted in immense damage, releasing the energy equivalent of 2.4 metric tons of TNT and wiping out 750 square miles.
   Astonishingly, 16 hours earlier that same day, an undetected meteor exploded over the Chelyabinsk Oblast of Russia, in the Ural Mountains region, on the border of Europe and Asia. According to calculations by Peter Brown at the University of Western Ontario, Canada, drawing on extremely low-frequency sound waves detected by a global network used to detect atomic bomb detonations, the object is estimated to have been about 56 feet across with a mass of 7,000 to 10,000 tons when it hit the atmosphere. It exploded with a force of nearly 500 kilotons of energy. The terminal part of the explosion likely occurred almost directly over the town of Chelyabinsk, causing extensive window breakage and some structural damage. Events of this magnitude are expected once every several of tens to 100 years.
   Meteorite impacts have caused significant damage to life on Earth in the distant past. It is theorized that a giant asteroid or comet hit the Earth about 65 million years ago causing an intense, global mass extinction. An estimated 75% of animals and plants, most notably non-bird like dinosaurs, took place in a geologically short period of time. One name for this event is the Cretaceous-Tertiary (K-T) extinction. Why we believe this event was caused by an impact with an extraterrestrial object was the discovery of high levels of the metal iridium in the boundary clay of that period worldwide. Iridium is rare on Earth but abundant in asteroids. The identification of the 110 mile wide Chicxulub crater in Mexico provided conclusive evidence that the K-T boundary clay represented debris from an asteroid impact.
   "Such an impact would have inhibited photosynthesis by generating a dust cloud that blocked sunlight for a year or less, and by injecting sulfuric acid aerosols into the stratosphere, which would have reduced sunlight reaching the Earth's surface by 10–20%. It would take at least ten years for those aerosols to dissipate, which would account for the extinction of plants and phytoplankton, and of organisms dependent on them (including predatory animals as well as herbivores). Small creatures whose food chains were based on detritus would have a reasonable chance of survival." -Wikipedia
   Those small creatures, which we now call mammals, are our ancestors. It is fortunate for us that this event took place or the dinosaurs would probably still rule the Earth, as they had for the 135 million years previously.
   Other things have caused mass extinctions. It is believed that their have been 5 of them in the distant past, the K-T being the most recent.
   About 200 million years ago the Triassic–Jurassic extinction event took place, causing the extinction of approximately half of all life on the planet, and was caused not by an asteroid impact (no evidence has been discovered for an impact), but by either gradual climate change, sea-level fluctuations, a pulse of oceanic acidification, or massive volcanic eruptions, causing the release of carbon dioxide or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter).
   As the K-T event was fortunate for us, the Triassic–Jurassic extinction event allowed the dinosaurs to flourish.
   The Permian–Triassic (P–Tr) extinction event of 252 million years ago killed off 96% of all marine species and 70% of terrestrial vertebrate species. It was the largest of the extinction events, and was the  only known mass extinction of insects. The cause of this event was probably the same as the Triassic–Jurassic.
   Then of course we have the Late Devonian extinction of 374 million years ago, which caused the loss of 19% of all families and 50% of all genera (a low-level taxonomic rank used in the biological classification of living and fossil organisms). The cause?  Possibly an impact, or plant evolution (plants got bigger. The covering of the planet's continents with massive photosynthesizing land plants in the first forests may have reduced carbon dioxide levels in the atmosphere. Since CO2 is a greenhouse gas, reduced levels might have helped produce climate change, cooling the planet, which then adversely affected those very same plants.
   Lastly we have the first extinction event, the Ordovician–Silurian of about 445 million years ago. At the time, all known life was confined to the seas and oceans. More than 60% of marine invertebrates died. This was probably caused by massive volcanism and weathering.
   As can be seen climate change probably accounted for 4 out of 5 of these events. Our climate is changing now and we our causing it, or at least our short sighted dependence on fossil fuels is causing it, spurred on by the fossil fuel industry's short sighted infatuation with short term monetary gains is causing it, spurred on by our politician's reluctance to do anything about it, including our current president.
   As Chris Hedges article below indicates, we have no other choice other than to stop our dependence on fossil fuels and switch to clean energy. We owe it to our children and their children. To allow this to go on the epitome of irresponsibility.
   If we don't change our ways the next extinction event, this one caused by ourselves, will be unfortunate for us, and fortunate for, oh, probably cockroaches, allowing them to rule the planet  for the next few million years or so.
   How sad it would be that we, the most intelligent creatures that have ever evolved on Earth, only lasted for 100,000 years.
   That doesn't say much for intelligence as a survival mechanism, now does it?

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