Sometimes called the Stratigraphy Prize, the ICS Medal recognizes a singular major achievement in advancing stratigraphic knowledge.
Sadler, who joined UC Riverside's Department of Earth Sciences in 1976, is being recognized by the ICS for CONOP (short for CONstrained OPtimization), software he developed to find and analyze the sequence of first- and last-appearances of thousands of fossil species that best fit the records of strata from hundreds of localities.
The award letter to Sadler notes that CONOP's "use in compiling and sequencing voluminous stratigraphic data is especially valuable, providing unique compilations of and insights into the stratigraphic record, and it is being widely applied."
ICS is the largest scientific body of the International Union of Geological Sciences. The ICS Medal is awarded once every four years to coincide with their International Geological Congress (IGC). Sadler will receive the medal in early August, when the IGC meets in Brisbane, Australia.
Fossil-bearing rock strata accumulate sporadically and patchily. Many layers are lost to denudation of Earth's surface; many fossils remain buried or undiscovered. This leaves gaps in our knowledge of earth history.
Early in his career, Sadler quantified the primary incompleteness of the fossil record by determining the inverse relationship between average rates of accumulation of fossil-bearing strata and the averaging time a phenomenon now called "the Sadler Effect."
"Gaps can be filled by combining the record of strata from numerous different localities gaps in one place may be filled by strata elsewhere," Sadler explained. "My CONOP software solves that computationally challenging task by analogy with the classic traveling salesman problem."
The traveling salesman problem has the salesman seek the shortest route that visits each of a large number of cities once and only once. He must visit cities in the order that incurs the lowest travel cost. The time required to evaluate all possible routes increases so rapidly with the number of cities that an exhaustive search for the best route is not feasible even for a computer, but very good solutions can be found by sophisticated algorithms. Instead of scheduling cities to minimize travel costs, the CONOP program finds a sequence of species originations and extinctions that minimizes the implied gaps in the fossil record.
CONOP finds the best-fit sequence by a trial-and-error mutation process that resembles evolution. Instead of building a solution bit-by-bit from the data, it works through a series of iteratively improved guesses about the whole solution. Each guess is compared with the data; the misfit between the current guess and data guides the next guess.
While CONOP is running this may take a week or two for large data sets its progress on screen appears as an animated curve of implied species richness through time, one frame for each new guess. As the fitness of the guesses improves, the curve progressively reveals times of radiation and extinction (that is, the rise and fall of the number of species) first the big extinctions, then the small details.
"If Hollywood can animate broomsticks and teapots, a UCR scientist should be able to animate standard scientific illustrations like a species richness curve!" Sadler quipped. "Besides providing some fun, the animations enable users to monitor the progress of the program and stop searches that go awry."
He added that the best-fit sequence of species appearance and disappearances is used to study ancient mass extinctions, to calibrate the geologic time scale (especially for the Paleozoic Era), and to correlate strata between oil wells.
Using CONOP, Sadler has sequenced the fossil record of several extinct groups of ancient marine organisms, including graptolites, conodonts, chitinozoans, and ammonites.
By continually mining the geoscience literature over the decades and writing his own data-management software, he maintains two research databases at UCR, now with hundreds of thousands of records. One database compiles measurements of accumulation rates of rock layers from intervals of seconds to billions of years; the other stores local first- and last-appearances of fossil species from thousands of localities.
"These databases continue to attract stimulating collaborations, and have led to invitations for me to teach about them at the Massachusetts Institute of Technology and in New Zealand, China, and Germany," Sadler said.
William Smith Lecture
Named for the man who prepared the first geologic map of England, the William Smith Lecture is given at the Geological Society of London's annual William Smith meeting. This year's meeting, to be held in early September, is titled "Strata and Time: An international conference to explore the relationship between the preserved strata of the rock record and the passage of time."
Sadler's lecture will focus on landscape denudation rates.
"I plan to discuss how short-term human influences on landscape change cannot be demonstrated merely by showing that short-term historical rates of change exceed background rates measured on geologic time scales," he said.
Provided by University of California - Riverside
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