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... , propose that the iridium layer was instead deposited through widespread volcanic activity. The proponents of an astronomical mechanism should be heartened by a recent paper in Nature, by W.S . Wolbach et al. Here is their Abstract: "Cretaceous-Tertiary (K -T ) boundary clays from five sites in Europe and New Zealand are 102 -104 -fold enriched in elemental C (mainly soot), which is isotopically uniform and apparently comes from a single global fire. The soot layer coincides with the Ir layer, suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled." The composition of the hydrocarbons in the sediments points to the earth's biomass (mainly surface vegetation) as the source of the soot. The total quantity of K ... Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Global fire at the k-t boundary The worldwide deposit of iridium at the K-T (Cretaceous-Tertiary) boundary has been considered very strong evidence that a large astronomical object (asteroid or comet) devastated our planet some 65 million years ago. Some scientists, however, propose that the iridium layer was instead deposited through widespread volcanic activity. The proponents of an astronomical mechanism should be heartened by a recent paper in Nature, by W.S . Wolbach et al. Here is their Abstract: "Cretaceous-Tertiary (K -T ) boundary clays from five sites in Europe and New Zealand are 102 -104 -fold enriched in elemental C (mainly soot), which is ...
Terms matched: 2 - Score: 100 - 15 May 2017 - URL: /sf060/sf060p11.htm
... of iridium at the end of the Cretaceous implies, to many at least, that the great biological extinctions of this period were the consequence of a meteorite impact. It has now been discovered that clay samples from the Cretaceous-Tertiary boundary also contain 0.36-0 .58% graphitic carbon. It is fluffy stuff and suggests that the planet was once covered by a thick layer of soot. Quantitatively, the soot layer is equivalent to the carbon in 10% of the earth's present biomass. The authors speculate that this soot was created by huge wildfires that consumed much of the earth's vegetation and perhaps fossil fuel as well. Terrestrial life was, of course, devastated -- just as it is in the currently popular "nuclear winter" scenarios. The ... worldwide deposit of iridium at the end of the Cretaceous implies, to many at least, that the great biological extinctions of this period were the consequence of a meteorite impact. It has now been discovered that clay samples from the Cretaceous-Tertiary boundary also contain 0.36-0 .58% graphitic carbon. It is fluffy stuff and suggests that the planet was once covered by a thick layer of soot. Quantitatively, the soot layer is equivalent to the carbon in 10% of the earth's present biomass. The authors speculate that this soot was created by huge wildfires that consumed much of the earth's vegetation and perhaps fossil fuel as well. Terrestrial life was, of course, devastated -- just as it is in the currently popular "nuclear winter" scenarios ...
Terms matched: 2 - Score: 77 - 15 May 2017 - URL: /sf043/sf043p14.htm
... bits of debris drifting downwards from the ocean's upper layers. This is the "marine snow." Its constituents are mainly: ". .. the tiny leftovers of animals, plants, and non-living matter in the ocean's sun-suffused upper zones. Among these particles are chains of single-celled plants called diatoms, shreds of zooplankters' mucous food traps, soot, fecal pellets, dust motes, radioactive fallout, sand grains, pollen, and pollutants. Microorganisms also live inside and on top of these odd-shaped flakes." Marine snow is everywhere in the ocean. Sometimes, it reaches blizzard proportions, and divers cannot see beyond a few feet. Measured in millimeters, the marine snowflakes are much larger than the average interplanetary dust particles ( ... : May-Jun 1994 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Marine Snow The marine analog of the high-altitude U2 used to collect interplanetary dust is the scuba diver armed with small jars and syringes. In these, marine biologists, such as A. Alldredge, collect the tiny bits of debris drifting downwards from the ocean's upper layers. This is the "marine snow." Its constituents are mainly: ". .. the tiny leftovers of animals, plants, and non-living matter in the ocean's sun-suffused upper zones. Among these particles are chains of single-celled plants called diatoms, shreds of zooplankters' mucous food traps, soot, fecal pellets, dust motes, radioactive fallout, ...
Terms matched: 2 - Score: 26 - 15 May 2017 - URL: /sf093/sf093b05.htm
