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Paleontology and Signal-Processing
I have just read an interesting article titled "Notes from the Underground"
by Alan Cutler of the NMNH at the Smithsonian, published in the Jan/Feb 1995
issue of The Sciences. The article is an explanation as to why there are no
dinosaur remains found at the KT boundary. The following are excerpts from
the article. I recommend it for an interesting approach to the
"Even the famed iridium layer, which many investigators consider
near-irrefutable evidence of a collision with an iridium-rich
extraterrestrial body, seems less impressive when viewed up close. In the
deep oceans, where sediments accumulate at the rate of millionths of a meter
a year, the iridium peak is smeared vertically through several centimeters
of sediment - hardly what one might expect of the debris from an
"... But in this case the event of record is a cosmic catastrophe that
killed all the dinosaurs in the world. Shouldn't the so-called iridium spike
be a little more spike-like? Shouldn't the concentration of bones in the
fossil record be, at very least, above average?"
"The ups and downs of life on earth constitute a signal, as real as the
voltage in a telephone wire or the rays of light striking your retina. In
that sence, a paleontologist studying the KT boundary resembles an
astronomer peering at a distant star. Just as the light reaching the
astronomer from the star is distorted by imperfect lenses and roiling
atmospheric gases, so the signal of the KT event reaching the
paleontologist is distorted by the imperfect record of life preserved in
sedimentary rock. And just as atronomers have devised a host of digital
signal processing techniques for sharpening blurred images and enhancing
contrast, paleontologists are starting to develop ways of squeezing as much
information as possible out of the fossil record. "
"... the mixing (of sediments) shifts upward and the particles (or bones)
are left behind as part of the historical record. In effect, mixing acts as
a convolution operation, and the mixing layer serves as the "kernel" ... In
the mixed ... record spikes in the abundance of species are attenuated and
tail off exponentially ... Thus the sudden extinction of a species shows up
not as an abrupt disappearance of fossils but as a gradual petering out."
(at least in marine sediments).
"... Anna Behrensmeyer and I developed just such a convolution model of
fossil preservation ... Starting with a hypothetical population of
dinosaurs, we estimated their normal annual mortality from ecological data
collected for large mammals in African wildlife preserves. Next, to estimate
what fraction of the dinosaur's bones would end up safely buried, we drew on
data from Behrensmeyer's 15 year study of the decay of mammal carcases in
Amboseli National Park. For our kernel we assumed that the layers were time
averaged over 100 years or more. Finally, we ran the model to see what sort
of bone spike would result if the entire population of dinosaurs suddenly
"The answer, we discovered, was no bone spike at all. For all reasonable
estimates of our parameters - annual mortality between 5 and 25 %, bone
burial at about 3% - time averaging completely swamped any such effect. Only
by assuming circumstances unusually favourable to preservation ... could we
raise the accumulation of bones above the normal background value."
"If normal mortality was 10% (to choose an intermediate value), 100%
mortality merely compresses 10 years of mortality into 1 year. In a record
that "convolves" several hundred years, that would hardly generate a blip.
Put another way, consider that the impact of an asteroid 10 km in diameter
would have increased the input of iridium to the earth almost 15,000,000
times above background level. Yet in most deep-ocean sediments that iridium
spike has been so smeared that it now measures less than 100 times the
background - a reduction by a factor of 150,000. Small wonder that the bones
of the dinosaurs left such a feeble signal."
I hope that this is not too long for the list. If so, please excuse me. It
was an insightful article about an area of paleontology that I had not
Toxic Chemicals Biologist by necessity,
By-stander and Observer of Paleontology by interest