50 dating Stevns

Identified in 1990 based on the work of Glen Penfield done in 1978, this crater is oval, with an average diameter of about 180 km (110 mi), about the size calculated by the Alvarez team.This dating is based on evidence collected in Northeast Mexico, including stratigraphic layers bearing impact spherules, the earliest of which is approximately 10 m (33 ft) below the K-Pg boundary.

Such a large impact would have had approximately the energy of 100 trillion tons of TNT, or about 2 million times greater than the most powerful thermonuclear bomb ever tested.The K–Pg boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period, the first period of the Cenozoic Era.Its age is usually estimated at around 66 Ma (million years ago), In 1980, a team of researchers consisting of Nobel prize-winning physicist Luis Alvarez, his son, geologist Walter Alvarez, and chemists Frank Asaro and Helen Michel discovered that sedimentary layers found all over the world at the K-Pg boundary contain a concentration of iridium many times greater than normal (30 times the average crustal content in Italy and 160 times at Stevns on the Danish island of Zealand).This would have further reduced the sunlight reaching the Earth's surface and then over several days, precipitated planet-wide as acid rain, killing vegetation, plankton and organisms which build shells from calcium carbonate (coccolithophorids and molluscs).Before 2000, arguments that the Deccan Traps flood basalts caused the extinction were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68 Ma and lasted for over 2 million years.

50 dating Stevns

However, there is evidence that two-thirds of the Deccan Traps were created within 1 million years about 65.5 Ma, so these eruptions would have caused a fairly rapid extinction, possibly a period of thousands of years, but still a longer period than what would be expected from a single impact event.The Deccan Traps could have caused extinction through several mechanisms, including the release of dust and sulphuric aerosols into the air which might have blocked sunlight and thereby reduced photosynthesis in plants.One of the consequences of such an impact is a dust cloud which would block sunlight and inhibit photosynthesis for a few years.This would account for the extinction of plants and phytoplankton and of organisms dependent on them (including predatory animals as well as herbivores).It would have taken at least ten years for those aerosols to dissipate.

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