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... Science Frontiers ONLINE No. 46: Jul-Aug 1986 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Which came first?The advent of complex life keeps getting pushed back farther and farther in time, as evidenced by the following abstract: "Microfossils resembling fecal pellets occur in acid-resistant residues and thin sections of Middle Cambrian in Early Proterozoic shale. The cylindrical microfossils average 50 x 110 microns and are the size and shape of fecal pellets produced by microscopic animals today. Pellets occur in dark gray and black rocks that were deposited in the facies that also preserves sulfide minerals and that represent environments analogous to those that preserve fecal pellets today. Rocks containing pellets and algal microfossils range in age from 0.53 to 1.9 gigayears ... Gyr) and include Burgess Shale, Greyson and Newland Formations, Rove Formation, and Gunflint Iron-Formation. Similar rock types of Archaean age, ranging from 2.68 to 3.8 Gyr, were barren of pellets. If the Proterozoic microfossils are fossilized fecal pellets, they provide evidence of metazoan life and a complex food chain at 1.9 Gyr ago. This occurrence predates macroscopic metazoan body fossils in the Ediacaran System at 0.67 Gyr, animal trace fossils from 0.9 to 1.3 Gyr, and fossils of unicellular eukaryotic plankton at 1.4 Gyr." (Robbins, Eleanora Iberall, et al; "Pellet Microfossils, Possible Evidence for Metazoan Life in Early Proterozoic Time," National Academy of Sciences, Proceedings, 82:5809, 1985 ...
Terms matched: 2 - Score: 294 - 15 May 2017 - URL: /sf046/sf046p14.htm
... 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 (but of ... interplanetary dust itself is also a constituent of marine snow). The bigger marine snowflakes -- over 0.5 mm -- are a major food source for deep-sea denizens waiting below for this manna from the watery heaven. The reason for mentioning marine snow in Science Frontiers is that biologists like Alldredge are really pio-neering new territory, where new anomalies must surely dwell. "' We've essentially discovered a whole new class of particles in the ocean that no one knew was there," she exults. .. .. . "' They're islands, really, where the metabolic activities of algae, bacteria, and protozoans produce unique chemical environments,' says Alldredge." To illustrate, the carbon content of bacteria on marine snow is 10, ...
Terms matched: 2 - Score: 155 - 15 May 2017 - URL: /sf093/sf093b05.htm
... Science Frontiers ONLINE No. 97: Jan-Feb 1995 Issue Contents Other pages Home Page Science Frontiers Online All Issues This Issue Sourcebook Project Sourcebook Subjects Possible Survival Of Giant Sloths In South America For many years, rumors have been filtering out of trackless western Amazonia telling of a 6-foot, 500-pound giant sloth clothed in reddish hair. Rubber gatherers of the region report that this fearsome creature emits a hideous odor and transfixes one with a paralyzing stare! It also seems impervious to spears and shotgun pellets. Natives and some cryptozoologists equate this animal to the legendary Mapinguari. P. J. Wynne's impression of South America's late-surviving giant sloth. D.C . Owen, an American biologist working with the Goeldi Natural History Museum in Belem, Brazil, has been tracking these stories. The present fossil record asserts that giant ground sloths resembling the supposed Mapinguari did occupy western Amazonia up to about 8700 years ago. To this must be added the appearance of an apparently fresh skin of the animal in 1897. Even more recently, gold miners are said to have killed a giant sloth. As with the North American Bigfoot, hard data are elusive, particularly actual specimens, dead or alive. Owen is optimistic, however. He sees his hunt for the Mapinguari as more than just another useless monster hunt: "If South America's largest terrestrial mammal has been hidden to science until 1994, what else does the Amazon have in terms of biodiversity that's new to us?" (Stolzenberg, William; "Bigfoot of the ...
Terms matched: 1 - Score: 15 - 15 May 2017 - URL: /sf097/sf097b07.htm
... day Technocrats, we will launch nucleararmed rockets that will nudge such cosmic threats into harmless trajectories. These Pollyannas are presumptious. They assume that asteroids are hard, cohesive objects that will be shoved aside by a few megatons of explosive energy. There are two things wrong with this idea, and these reveal how radically our ideas about the nature of asteroids have changed in just 10 years. First, most astronomers will now agree that asteroids are orbiting rubble piles rather than monolithic objects. For example, the near-earth asteroid Mathilde, 53 kilometers in diameter, has a density of only 1.3 grams/cubic centimeter. Its porosity must be greater than 50%. It is not a hard, coherent object. Instead of a bullet, it is more like a cloud of shotgun pellets. It would be hard to divert all this debris with a nuclear blast. To make matters worse, asteroids like Mathilde are stickier than a cloud of buckshot. This fact is deduced from photos of asteroids showing many to be marked by huge craters. (Mathilde has one 33 kilometers wide.) K.R . Housen et al, using laboratory tests and scaling data, argue that asteroid craters were not blasted out by collision. (Mathilde is not "shattered" as one would expect given such a huge crater.) Rather, the craters are "dents" instead of holes! Cosmic rubble piles are like sponges. Collisions with other rubble piles result in compression of the target surface and accretion of the smaller object. In effect, asteroids are energy absorbers and will hardly ...
Terms matched: 1 - Score: 14 - 15 May 2017 - URL: /sf127/sf127p03.htm
