Interplanetary Dust Particle. Linked from Washington University in St Louis Laboratory for Space Sciences.
A Dusty Young-Earth Argument Backfires
Interplanetary Dust Particle. Linked
from Washington University in St
Louis Laboratory for Space Sciences.
After arguing for decades that the accretion rate of interplanetary dust particles (IDPs) to the moon and earth contradicts the accepted, multibillion-year age of the solar system, young-earthers have now for the most part abandoned the argument (Snelling and Rush, 1993). Indeed, the evidence is such that they could hardly do otherwise. However, it is should be further recognized that the IDP flux rates determined from analyses of Cretaceous and younger deep sea sediment cores are in excellent agreement with the modern flux, as determined from satellite and other other data. The simplest explanation of this fact is that a) the ET flux rate has remained relatively constant, and b) the sedimentation rates determined for deep sea cores by radiometric data, from one to a few mm per 1000 years, are accurate. This of course contradicts both Young-Earthism and Flood Geology. Thus, the argument from interplanetary dust accretion not only fails to support YEC, it provides compelling evidence against YEC.
Introduction to IDPs
The earth's surface is constantly being rained upon by interplanetary dust particles (IDP's), from a few to several hundred micrometers in diameter. The mass distribution of this dust flux peaks at around 200µm (Love and Brownlee, 1993). This dust is thought to be derived from collisions of asteroidal material and from comets (e.g. Kortenkamp and Dermott, 1998). The majority of IDPs are compositionally similar to chondritic meteorites (Jessberger et al, 2001), and quite distinct from crustal rocks on earth. For instance, siderophile elements such as Iridium and Osmium are enriched and have distinct isotopic ratios in IDPs, compared to crustal rocks. These characteristics make possible the recognition and quantification of IDPs in the sedimentary record (Kyte, 2002).
The Modern IDP Flux
There have been many attempts to measure the flux of IDP to the earth's surface, based on a variety of methods. The earliest attempts were based on geochemical proxies, such as nickel content. For instance, Petterson (1960) estimated a flux rate of up to 14,000,000 metric tons/yr. This completely obsolete estimate is the only one cited by Morris (1974), Huse (1991), Walter Brown (n.d.), and many other proponents of YEC. Of course, even before 1974, it was clear that a rate of 14,000,000 tons per year is orders of magnitude too high. Barker and Anders (1968) for instance estimated a flux rate of 50-150 x 10^4 metric tons/ yr, based on analyses of Ir and Os in deep-sea sediments.
It has recently become possible to directly measure the flux and mass-distribution of IDPs directly, based on cratering data from control panels on NASA's Long Duration Exposure Facility satellite. Analyses of cratering patterns on the LDEF panels indicate a global IDP flux of 40±20 x 10^4 metric tons/ yr. This agrees well with previous accretion rate estimates based on analyses of sediment and ice cores. Ganapathy (1983) for instance estimated a global flux rate of 47-149 x 10^4 metric tons/ yr, based on analyses of Iridium in an antarctic ice core. Ganapathy's Ir profile also shows a several-fold enrichment at the core level corresponding to 1912±4, which is attributed to the Tunguska event of 1908. The recent flux rate is now firmly established to be ~30-40±20 x 10^4 metric tons/ yr (Love and Brownlee, 1993; Peucker-Ehrenbrink, 1996: Kortenkamp and Dermott, 1998; Peucker-Ehrenbrink and Ravizza, 2000). Even the YECs Snelling and Rush (1993) agree that the dust flux is well constrained with a value about 10-100 x 10^4 metric tons/ yr. Thus, the value of 14,000,000 tons per year used by Morris (and other creationists) is between 1400 and 140 times too large. The graphic below illustrates a compilation of ~60 flux rate estimates, based on a variety of methods:
From the Noble Metals Group Webpage at the Woods
Hole Oceanographic Institute.
The IDP Flux Through Geologic Time
Rates of IDP accretion through geologic time have been deduced from isotopic analyses of slowly-deposited deep-sea clays, dating from the Cretaceous to the Recent. These types of analyses are considered the most reliable, because they sample a much larger 'area-time product' than ice cores and and satellites (Peucker-Ehrenbrink and Ravizza, 2000), and thus reduce the affects of sampling artifacts, and because there is virtually no contribution from detrital sediment.
In order to calculate a flux rate from these sediment cores, it is necessary to determine independently the sedimentation rate. This involves the use of radiometric dating. The sedimentation rate (typically 1-100mm/1000 yr) may be determined by averaging between biostratigraphic stage boundaries, using radiometric dates for those stage boundaries, or by time-averaging between two radiometric-dated magnetostratigraphic boundaries, or by direct 230Th/234U dates along the core. The point here is simply that the accuracy of the IDP flux rate is crucially dependent upon the accuracy of the radiometric dates used to determine the sedimentation rates. If those dates are accurate, and if the IDP flux rate has remained steady, then the flux rates determined from such analyses should closely match those from modern satellite measurements.
These expectations seem to be supported by the data. The flux rates determined over geologic time from Osmium and Iridium isotope systematics agree closely with modern satellite measurements of the ET dust flux. Peucker-Ehrenbrink (1996) review Osmium isotope data from Pacific deep-sea cores spanning the past 80 million years. Their data set consists of 19 samples from several different cores. Their review "indicates no systematic variation in the mean flux of ~37,000±13,000 tons/a over the past 80Ma, except at the K-T boundary. The magnitude of the flux is similar to the bulk ET matter flux based on 423 Ir-MAR [mass-accumulation rate-ed] data pairs from the pelagic sediment cores DSDP site 596 and LL44-GPC3" (p. 3193). Peucker-Ehrenbrink and Ravizza (2000) note that "[t]he global flux of ET matter to the seafloor, calculated at 30,000±15,000 metric tons per year using Os isotope data for the most suitable marine sediment samples, agrees with the flux of ET matter derived from the LDEF study (40±20 x 10^4 metric tons per year; love and Brownlee, 1993) within uncertainty" (p. 1969). The graphic below, from Peucker-Ehrenbrink (1996), illustrates this agreement. The horizontal lines represent the flux rates deduced from satellite observations (Love and Brownlee, 1993).
From the Noble Metals Group Webpage at the Woods
Hole Oceanographic Institute.
Conclusion
Snelling and Rush (1993) make an amusing understatement when at the end of their article on "moon dust" they observe that the conclusions of their article are "unfortunately are not as encouraging or complimentary for us young earth creationists as we would have liked." Although to their credit they clearly state that the 'dust problem' does not contradict the accepted multibillion-year timescale and should not be used as an argument for young-earthism, they do not attempt to explain why the flux rates determined from radiometric dating of supposed flood sediments would happen to match those derived from modern satellite and ice core measurements.
References
Barkers, J.L., and Anders, E., 1968. Accretion rate of cosmic matter from Iridium and Osmium contents of of deep-sea sediments. Geochimica et Cosmochimica Acta 32, pp. 627-645.
Esser, B.K. and Turekian, K.K., 1988, Accretion rate of extraterrestrial particles determined from osmium isotope systematics of Pacific pelagic clay and manganese nodules. Geochimica et Cosmochimica Acta 52, pp. 1383-1388.
Ganapathy, R., 1983. The Tunguska explosion of 1908: discovery of meteoritic debris near the explosion site and at the south pole. Science 220, pp. 1158-1161.
Huse, S.M., 1991. The Collapse of Evolution. Baker Book House Company, Grand Rapids, MI.
Kyte, F. T. and Wasson, J.T., 1986. Accretion rate of extraterrestrial matter: iridium deposited 33 to 67 million years ago. Science 232, pp. 1225-1229.
Kyte, F.T., 2002. Tracers of the extraterrestrial component in sediments and inferences for Earth's accretion history. In: Koeberl, C., and MacLeod, K., Catastrophic Events and Mass Extinctions: Impacts and Beyond. GSA Special Paper 356, pp. 21-38.
Love, S. G., and D. E. Brownlee, 1993. A direct measurement of the terrestrial mass accretion rate of cosmic dust, Science 262, pp. 550-553.
Morris, H. M., 1974. Scientific Creationism, Creation-Life Publishers, San Diego.
Pettersson, H., 1960. Cosmic spherules and meteoric dust. Scientific American, 202, pp.123-132.