RE: [asa] ICR for January 2007: crisis in crater count dating

Is there merit to this article?

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From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu] On
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Sent: 03 January 2007 22:13
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Subject: [asa] ICR for January 2007

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BACK TO GENESIS: BTG 217(d) - Crisis in Crater Count Dating

Dating methods are like human pyramids; they depend ultimately on the
support of the bottom layer. Picture an inverted pyramid. If the
bottom guy buckles under pressure, the circus act quickly turns into
a dogpile. One widely used technique for estimating ages of planetary
surfaces is in similar jeopardy.

Read it at: http://www.icr.org/article/3139/
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217d - Crisis in Crater Count Dating (#217)
by David F. Coppedge
Abstract

Dating methods are like human pyramids; they depend ultimately on the
support of the bottom layer. Picture an inverted pyramid. If the bottom guy
buckles under pressure, the circus act quickly turns into a dogpile. One
widely used technique for estimating ages of planetary surfaces is in
similar jeopardy. Its underlying assumption, unquestioned for decades, has
recently been found to be seriously flawed.

Crater-count dating seems perfectly logical: the more craters, the older the
landscape. It assumes, however, that impactors arrive at a roughly steady
rate and produce one crater per hit. After compensating for various
complicating factors, like atmospheric density, gravity, and geological
activity, scientists had been confident of their time charts -- until
recently. New thinking about "secondary craters" has thrown this whole
foundation of comparative planetary dating into disarray.

Secondary craters are those formed from the debris of an initial impact. If
a sufficiently massive body hits a planet or moon, the debris cloud tossed
upward will contain many pieces big enough to fall back and form more
craters. Planetologists were not unaware of secondary cratering, but until
recently, underestimated its significance. Now they are finding that the
vast majority of craters could be secondaries. One writer in Nature
estimated that a single large impact on Mars could generate ten million
secondaries, and that 95% of the small craters on Europa could be from
fallback debris.

Without a way to reliably identify secondary craters, only subjective
inferences can be made about the history of a surface. One might suppose
secondaries could be identified by proximity to a large crater, or by
similar amounts of erosion or space weathering. It's not so simple. Some
debris could go into orbit only to fall back centuries later, while other
pieces could escape into space to eventually impact other bodies. Fallback
debris could also cast dust over the primary craters, obscuring the
relationship, or could even toss up more debris to generate additional
impacts.

Believing they knew how old the earth-moon system was, and something about
its geological history, scientists had plotted crater density on the moon
against surface age. They applied this to Mars and other planets and moons,
such that any surface could be dated by reference to the lunar standard. A
pyramid was thus built on a shaky assumption. Now, awareness of the
potential for single impacts to generate vast numbers of secondary craters
has yanked the guy on the bottom, bringing the scheme crashing down. Science
(May 26, 2006) reported that at a conference last March, "125 planetary
scientists deadlocked" over how to apply the method, with many doubting that
crater counts have anything to do with telling time. Geological dates
inferred from the method could be "off by orders of magnitude."

A brief discussion like this cannot begin to place crater formation within a
Biblical timescale. A full creationist model of cratering in the solar
system will require much work. There is an important lesson here, though,
for all science lovers: question assumptions.

*David F. Coppedge works in the Cassini program at the Jet Propulsion
Laboratory.

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Received on Thu Jan 4 17:51:21 2007