Autor Thema: Neues Analyseverfahren auf der Grundlage von 'Impact spherules'  (Gelesen 1070 mal)

Offline karmaka

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Neues Analyseverfahren auf der Grundlage von 'Impact spherules'
« am: April 25, 2012, 22:14:36 Nachmittag »
Neues Analyseverfahren auf der Grundlage von 'Impact spherules'

Neues Analyseverfahren zur Bestimmung der Größe und Einschlaggeschwindigkeit
von Asteroiden in der Frühzeit der Erde auf der Grundlage von 'Impact spherules' in der Reivilo Schicht in Südafrika

Impact Spherules: Record of an Ancient Heavy Bombardment of Earth, B. C. Johnson and H.J. Melosh, Nature (2012).

Impact craters are the most obvious indication of asteroid impacts, but craters on Earth are quickly obscured or destroyed by surface weathering and tectonic processes1. Earth's impact history is inferred therefore either from estimates of the present-day impactor flux as determined by observations of near-Earth asteroids, or from the Moon's incomplete impact chronology. Asteroids hitting Earth typically vaporize a mass of target rock comparable to the projectile's mass. As this vapor expands in a large plume or fireball, it cools and condenses into molten droplets called spherules. For asteroids larger than about 10 kilometers in diameter, these spherules are deposited in a global layer. Spherule layers preserved in the geologic record accordingly provide information about an impact even when the source crater cannot be found. Here, we report estimates of the sizes and impact velocities of the asteroids that created global spherule layers. The impact chronology from these spherule layers reveals that the impactor flux was significantly higher 3.5 billion years ago than it is now. This conclusion is consistent with a gradual decline of the impactor flux after the Late Heavy Bombardment.

Splatters of molten rock signal period of intense asteroid impacts on Earth, raise questions about the source of impactors

An Archaean heavy bombardment from a destabilized extension of the asteroid belt

    William F. Bottke et al.

 :hut: Martin

Offline schwede-jens

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Re: Neues Analyseverfahren auf der Grundlage von 'Impact spherules'
« Antwort #1 am: April 26, 2012, 07:41:45 Vormittag »
Hej Martin,

mal wieder hoch interessant, was du da aufgestöbert hast!!!!



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