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DINOSAUR EXTINCTION
WHAT IS EXTINCTION?
K-T ASTEROID THEORY
OTHER K-T EXTINCTION THEORIES
STUDYING EXTINCTIONS

STUDYING EXTINCTIONS

Scientists learn about extinctions by studying the fossil record and the chemical composition of rocks and chemicals around excavation sites. Looking at the relative abundance of fossil families in a rock layer indicates whether or not plant and animal families in the world at that time were thriving and diversifying or in decline.


MASS EXTINCTIONS

A mass extinction will appear in the rock layers as a dead zone (containing few fossil remains) between layers with evidence of extensive life above and below it. The dead zone represents the time of a mass extinction and its aftermath.

Examining the chemical content of the rock strata gives clues about the causes of the extinction, including information about the climate, volcanic activity, extensive fires (soot would appear in the layers), flooding , cosmic collisions (meteorite impacts add rare elements and alter existing rocks), etc.


ESTIMATING DATES

The study of extinctions is based on the fossil record, which is incomplete and skewed (for example, some organisms fossilize less readily than others and are therefore underrepresented in the fossil record). Dating the extinction (and also the first appearance) of a species is difficult, if not impossible. Dating known fossils can only give a range for the lives of that particular group organisms, not the entire species; the known fossils of an organism are only a minuscule subset of the original species.

Rarer fossils will yield even less accurate estimates than the more common fossils. Rare fossils may be rare because there were a small number of organisms to begin with, or because that organism is underrepresented in the fossil record. Since these fossils are less abundant, the chances of a fossil being found is low, causing the date estimates to be based on incomplete data.

There are other difficulties inherent in interpreting the fossil record. The Signor-Lipps Effect explains how a fossil record that appears to be a gradual extinction could actually represent a sudden extinction. If many organisms go extinct at the same time, the fossil record wouldn't necessarily represent the rarer species and the more common equally. The rarer species might disappear from the fossil record long before the time of extinction, simply due to chance.


DATING ROCK LAYERS

First the rock layers must be dated, by using some of the following methods:

CHEMICAL ANALYSIS OF THE SITE

A chemical and mineral analysis of the dead zone reveals much about conditions at the time of the extinction.

WHAT IS EXTINCTION?
CRETACEOUS ASTEROID THEORY
OTHER K-T EXTINCTION THEORIES
STUDYING EXTINCTIONS




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