How Good is the Fossil Record?
Carbonates vs Clastics One of the major uncertainties in getting information from the fossil record is what paleontologists call time resolution: how many years of accumulation does a single sample of fossils actually represent? That is, how many generations have been mixed or “time averaged?” Magnitudes of time averaging (total range in shell ages) have ranged from 10 to 10,000 years, and occasionally longer. Shells are thus able to survive the forces of destruction for much longer than the life-spans of the animals that made them. Most of this information, however, has come from analysis of non-limy or clastic sediments in the temperate zone. Now a new study by Susan Kidwell of the University of Chicago and colleagues is the first to measure time averaging on tropical limy bottoms that are more similar to many ancient fossil assemblages. Kidwell and her colleagues examined shells and sediments off the Caribbean coast of Panama. They found that clastic sediments contain significantly
