I've been wanting to post in this topic for a while, and finally just decided to go ahead and do so. Part of my dissertation (just finished!) included a calculation of meteorite fall rates and a determination of the amount and types of material that fall to the Earth per year. While I'm not an expert on this subject, the research material is intriguing. I find it somewhat amusing when the meteorite dust is used for a young earth when it's been shown very clearly that meteorite dust fall rates correlate very well with an old Earth, and, in fact, make a young Earth / Noah's flood geology impossible.

At present, we receive ~3 x 10

^{7} kg of meteoritic dust over the surface of the Earth per year (Love and Brownlee, 1993), and is a bit better constrained than the Dohnanyi calculation. This value is known from sky observations, deep ocean cores, ice cores, and a number of other methods, so it's pretty well established. Meteoritic dust is substantially enriched in the element iridium by about a factor of 100 over the crustal abundance (Lodders and Fegley 1998), which is what allowed Alvarez to propose a meteorite impact caused the extinction of the dinosaurs 65 million years ago.

Kyte and Wasson (1984) analyzed a series of deep sea sediment cores dated from the past 50 million years and calculated the fraction of extraterrestrial material from the concentration of iridium in this dust. Knowing the rates of deposition for this material, they then determined the fall rates necessary to provide this extraterrestrial iridium. And lo and behold, the extraterrestrial material fall rates calculated by Kyte and Wasson (1984) closely matched the Love and Brownlee (1993) rates.

This means that the present day meteorite flux rates and the flux rates for the last 50 million years or so have not changed significantly. The meteorite fall rate for old rocks correlates with what we see now, which is a strong correlation for an old Earth.

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Conversely, we could calculate what might happen if we had to fit 4.5 billion years of geology in one year, as Flood geology would require. Since the iridium concentration is fairly constant throughout the whole of the deep sea cores examined, a flood geologist would have to assume that during the flood, the fall rate meteorites would have to be equivalent to fitting 4.5 billion times the present day meteorite flux into one year. So:

3 x 10

^{7} kg x 4.5 x 10

^{9} years worth of meteorite flux

=1.35 x 10

^{17} kg of meteoritic material fell during the flood year.

The energy imparted by this amount of material is equal to:

1/2 M V

^{2}, where M is the mass of the extraterrestrial material, and V is the velocity at which it falls to the Earth (equal to the escape velocity, or 11200 m/s). This gives:

1/2 (1.35 x 10

^{17} kg) * (11200 m/s)

^{2}= 8.5 x 10

^{24} Joules.

So the Earth's atmosphere would have had to accomodate 8 x 10

^{24} J of energy from this falling meteorite matter. We can do a quick calculation to determine the amount of heating this would cause:

Energy = M

_{atmo} * Cp *(T), where M

_{atmo} is the mass of the atmosphere (5 x 10

^{18} kg), Cp is the pressure constant for air (about 716 J/kg * K for N2), and T is the temperature change of the atmosphere. Solve for T:

T = Energy/ (M

_{atmo} * Cp)

= 8 x 10

^{24} J / ((5 x 10

^{18} kg) *716 J /kg * K)

= 2,400 K.

So the temperature change of the Earth's atmosphere would be about a 2,400 K increase. Pretty toasty for that poor boat! This even gets worse when we have to consider the late heavy bombardment!

Refs:

Kyte, F.T. and Wasson, J.T., 1986, Accretion rate of extraterrestrial material: iridium deposited 33 to 67 million years ago. Science 232, 1225-1229.

Lodders, K. and Fegley, B., 1998, The Planetary Scientist’s Handbook. Oxford University Press, Oxford, UK, 371 pp.

Love, S.G. and Brownlee, D.E., 1993, A direct measurement of the terrestrial massaccretion rate of cosmic dust. Science 262, 550-553.