Cartoons in a pamphlet of A. Lund on the comet in 1857, allegedly to destroy the Earth in June, the 13th of that year (at the end of the kite has not yet decided to appear in the public domain image).
Single cause - the Chicxulub impact (in some interpretations, means "the devil's tail"), a meteorite - the faunal turnover at the end of the Cretaceous should explain all the observed changes in the fossil record. According to the scenario is the most popular mass extinction is mainly due to the consequences of the effect: the pressure wave storms and fire, were soon after the release of large amounts of gas vaporized rocks, rich in carbonates and sulfates. Gases react to form acid rain, water vapor and dust in the atmosphere solar irradiance blocked, causing a "nuclear winter" and blocking the photosynthetic activity of terrestrial plants, especially phytoplankton in the oceans. Without plants, not just the food chain collapsed.
A number of major groups of organisms have disappeared, and nonavian dinosaurs, marine and flying reptiles, the Ammonites, the main reef-building rudist clams or as well as mammals and dinosaurs modern bird has suffered drastic losses . Unlike other large terrestrial vertebrates that reptiles and amphibians in particular, are considered vulnerable to chemical or thermal modification of the environment, only a few casualties. Also insects, organisms spread now and then, shows almost no change. Terrestrial plants show mixed results, and some research suggests that after the destruction of vegetation by fire and inhibited the photosynthetic activity of ferns spread throughout the devastated landscape. But this increase of fern spores in the sediments, also called fern spike, which is known only to the few places in North America and a place in New Zealand, it is not (yet?) Found in sediment Eurasia.
In the realm of marine calcareous nannoplankton (as Coccolithophorids) and planktonic foraminifera (calcareous shells) decreased significantly, but the benthic foraminifera, diatoms, dinoflagellates and radiolarians (silica shells) show virtually no response. Brachiopods show marked decrease in diversity, however, molluscs (except rudists), gastropods and bivalves as weak shows a decline over time.
The disappearance of organisms with calcareous shells was seen as a consequence of acid rain and has changed the chemistry of the oceans and lakes. However, this scenario is in conflict with the survival of susceptible animals such as amphibians. Like many bivalves, gastropods and echinoderms, probably (the fossils of this group is not well studied) - organisms protected by calcareouhttp://www.blogger.com/img/blank.gifs shells or plates - show no significant changes.
The hypothesis of the effect of phototrophic phytoplankton survived decreased solar radiation and temperatures decreased by forming resting spores, however, radiolarians have thrived during the Cretaceous-Paleogene, and these bodies do not produce spores!
The dinosaur fossil record shows that fish almost 90% of the families have survived, it is difficult to explain if we assume that the base of the food chain, phytoplankton, has been greatly reduced by the effects of impact. Strange marine predators such as sharks and large reptiles, has experienced a significant total collapse.
Taking into account only some groups, such as planktonic foraminifera, nannoplankton, brachiopods, the Ammonites, and large reptiles, their decline can be explained by surface effects of impact on Earth's oceans. However, other organisms such as radiolarians, most molluscs, echinoderms, fish, and that flourished simultaneously in the same environment. The same pattern is observed in the terrestrial realm, some groups have suffered heavy losses, some people seem to be falling, but survived in the Paleogene, and some show no change.
Scenario at a glance, the answer for bodies at the end of the Cretaceous mixed model view, difficult to explain only a cause, or seem to be becoming more common.
A major problem has been prescribed, the period within which all these different groups experienced a decline or completely extinct. Places where a complete Cretaceous-Paleogene stratigraphy of the transition line are rare and most studied sites (especially in land deposits) are found in North America, probably the closest the effect. Available worldwide profiles are still few and far between, and scattered to decide if a meteorite was the only reason for the world and the sudden mass extinction.
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Posted by Dinosaurs World at 9:34 PM