Hai.... I'm New....... -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Sunday, September 01, 2002 8:02 AM To: [EMAIL PROTECTED] Subject: [iagi-net] Digest Number 22
------------------------ Yahoo! Groups Sponsor ---------------------~--> 4 DVDs Free +s&p Join Now http://us.click.yahoo.com/pt6YBB/NXiEAA/MVfIAA/jFYolB/TM ---------------------------------------------------------------------~-> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] ------------------------------------------------------------------------ There are 2 messages in this issue. Topics in this digest: 1. [iagi-net-l] Asteroid impact hazards "greatly overstated" From: "Rovicky Dwi Putrohari" <[EMAIL PROTECTED]> 2. [iagi-net-l] Volcanos a bigger threat than comets From: "Rovicky Dwi Putrohari" <[EMAIL PROTECTED]> ________________________________________________________________________ ________________________________________________________________________ Message: 1 Date: Sat, 31 Aug 2002 23:47:53 +0800 From: "Rovicky Dwi Putrohari" <[EMAIL PROTECTED]> Subject: [iagi-net-l] Asteroid impact hazards "greatly overstated" Asteroid impact hazards "greatly overstated" Jeff Hecht New Scientist, 2002-01-30 If A collision with an asteroid is going to finish us off, it will have to be a lot larger than anyone thought, according to a controversial new study of the impact that wiped out the dinosaurs. Virtually everyone agrees that the asteroid that hit Chicxulub in Mexico 65 million years ago killed the dinosaurs, but how it did so is unclear. A long-standing theory is that clouds of dust hung in the upper atmosphere for months, blocking sunlight and stopping plants growing. But no one is sure that this is really the reason, and finding out is critical for assessing the risk asteroids pose to humanity. Now geologist Kevin Pope of Geo Eco Arc Research in Aquasco, Maryland, is claiming that dust cannot have been to blame. Only dust grains smaller than a micrometre across stay suspended in the atmosphere, and Pope says that the 10-kilometre asteroid would not have created enough fine dust to have a global effect. Instead he thinks sulphur from the rocks vaporised by the impact may have formed sulphate aerosols that blocked out the light. He says earlier overestimates of dust levels mean that the hazards from an asteroid impact today have been "greatly overstated". Particle uncertainty The Chicxulub impact spread debris across the globe, which settled to form a layer averaging 3 millimetres thick--that's a few trillion tonnes of material. But having reviewed previous work on the subject, Pope says that more than 99 per cent of the layer is made up of spherules--droplets that condensed from vaporised rock. Only the remaining 1 per cent of the debris consisted of rock pulverised directly into dust. It's still uncertain what the size distribution of that dust would have been, but from studies of volcanic dust, Pope deduces that less that 1 per cent of it consisted of particles smaller than 1 micrometre. That's only 100 million tonnes--about 10 times as much dust as was released by the 1991 eruption of Mount Pinatubo, which had a barely measurable effect on global climate. But other researchers aren't convinced that the impact produced so little dust. Jan Smit of the Free University in Amsterdam points out that volcanic dust isn't formed in the same way as impact dust, so the particle sizes wouldn't necessarily be the same. He says his studies of iridium in the impact layer suggest that at least half of it is in particles smaller than 0.1 micrometres. Even if Pope is right, we can't rest easy just yet. "Other things will get you," says Brian Toon, an atmospheric scientist from the University of Colorado in Boulder. He believes the effects of an asteroid impact would be apocalyptic - filling the entire sky with fiery meteors as the debris rained back down onto the atmosphere. "Everything on the surface is going to catch fire," he predicts. But despite all the debate, much still depends on guesswork. "We know so little about impacts," says theoretical geophysicist Jay Melosh of the University of Arizona. "The uncertainties are at least a factor of five." Journal reference: Geology (vol 30, p 99) =================== --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] Visit IAGI Website: http://iagi.or.id IAGI-net Archive 1: http://www.mail-archive.com/iagi-net%40iagi.or.id/ IAGI-net Archive 2: http://groups.yahoo.com/group/iagi ===================================================================== Indonesian Association of Geologists [IAGI] - 31st Annual Convention September 30 - October2, 2002 - Shangri La Hotel, SURABAYA ________________________________________________________________________ ________________________________________________________________________ Message: 2 Date: Sat, 31 Aug 2002 23:50:14 +0800 From: "Rovicky Dwi Putrohari" <[EMAIL PROTECTED]> Subject: [iagi-net-l] Volcanos a bigger threat than comets Yang lebih menakutkan justru malah gunung api. dimana Indonesia ini merupakan 1/3 ring of fire (rentetan gunung api di Asia Pasific) Toba, Sumatra meletus 73 000 tahun lalu, padahal siklus gunung meletus besar biasanya setiap 50 000 sedang impact meteor tiap 100 000 tahun sekali. Kayaknya manusia ini sukanya mencari penyebab dari luar. Padahal kemungkinan "threat" lebih banyak ya dari dalam bumi sendiri. Yang mambahayakan kita .... ya kita sendiri kali ya ... rdp ================= Volcanos a bigger threat than comets A volcanic super-eruption could pose twice as much of a threat to civilisation as a collision with an asteroid or comet. Every 100,000 years, a cosmic body with a diameter of more than one kilometre slams into the Earth but Michael Rampino, of New York University, warned that a massive volcanic eruption capable of causing as much devastation occurs once every 50,000 years. "Volcanoes in Yellowstone Park and Long Valley in California have erupted three times in the past 1 million years, each time coating the whole of the US with ash," New Scientist magazine said. "But the biggest and most recent super-eruption happened at Toba, on the island of Sumatra, 73,000 years ago." According to Mr Rampino's research, Toba blasted a crater 100 kilometre long and sent 3 billion tonnes of sulphur dioxide into the atmosphere and a dense volcanic cloud around the globe. "He also suspects that Toba's super-eruption was responsible for the population crash of 70,000 years ago, when the number of people fell to no more than 10,000," the magazine added. Ash and aerosols from super-eruptions block the sun and send global temperatures plummeting. Another Toba super-eruption could push temperatures down and cause regional cooling, according to Mr Rampino. "That's going to kill off most of the above-ground vegetation in Africa," he said, adding global vegetation could be reduced by 25 per cent. --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] Visit IAGI Website: http://iagi.or.id IAGI-net Archive 1: http://www.mail-archive.com/iagi-net%40iagi.or.id/ IAGI-net Archive 2: http://groups.yahoo.com/group/iagi ===================================================================== Indonesian Association of Geologists [IAGI] - 31st Annual Convention September 30 - October2, 2002 - Shangri La Hotel, SURABAYA ________________________________________________________________________ ________________________________________________________________________ Your use of Yahoo! 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