Archean impact

[zankaon]

What would it be like if a 300 km diameter meteorite hit the early (first 1 Byrs) Archean surface?

Hint: a smaller impact on Kilawea surface in Hawaii.

[Xnn]

Global tsumani...

Correlation of Earth's oldest documented impact layer between the EPB of Western Australia and the BGB of South Africa is consistent with our previous work indicating that these early Archean impacts were very large: 10 to 100 times more massive than the Cretaceous-Tertiary event, producing unusual impact-generated tsumanis (3, 7, 14, 16). This report confirms the global nature of these massive fallout layers, suggests that an early terrestrial record of large asteroidal impacts does exist, and may provide important constraints on the evolution of Earth's geological and biological systems.

http://www.sciencemag.org/cgi/content/full/297/5585/1325

[zankaon]

What would it be like if a 300 km diameter meteorite hit the early (first 1 Byrs) Archean surface?

Hint: a smaller impact on Kilawea surface in Hawaii.

such Archean surface (not crust) would have no silicates, since anoxic environment. so seemingly not much ejected material into atmosphere. So except for direct hit, seemingly not much of a geological effect?

[joelupchurch]

There is a web page for doing impact calculations:

http://www.lpl.arizona.edu/impacteffects/

[negitron]

such Archean surface (not crust) would have no silicates, since anoxic environment. so seemingly not much ejected material into atmosphere.

Says who? Ejecta is going to be thrown up regardless of the crustal composition. In an asteroid impact, huge portions of both the crust and the impactor are almost instantaneously vaporized and even larger portions surrounding the impact site are pulverized. The expanding vaporized material blows the pulverized stuff outward as it blasts out the crater. The crust could be made of solid iron and you'd still have massive amounts of material ejected into the upper atmosphere.

[zankaon]

such Archean surface (not crust) would have no silicates, since anoxic environment. so seemingly not much ejected material into atmosphere. So except for direct hit, seemingly not much of a geological effect?

Such shallow Archean sea impact would vaporize impacted water, which is compressable, as well as extruded into atmosphere. Hence wouldn't there seem to result in an inflow of surrounding waters into vaporized volume of water? Perhaps after any outgoing wave.

[ideasrule]

Such shallow Archean sea impact would vaporize impacted water, which is compressable, as well as extruded into atmosphere. Hence wouldn't there seem to result in an inflow of surrounding waters into vaporized volume of water? Perhaps after any outgoing wave.

Yes, and the incoming water creates a kilometers-high jet of water after filling the void. The collapse of this jet is the main cause of the tsunamis.

[Ophiolite]

"such Archean surface (not crust) would have no silicates, since anoxic environment"

The above statement is incorrect. Silicates will automatically crystalise from silicate melts, which in turn are the natural product of a proto-planet heated by gravitational contraction, impacts and considerable radioactivity. Since oxygen is the commonest element in the mantle and the crust (and probably, on balance, in the whole Earth) one can hardly describe the enviroment as anoxic.