investigating life
“You are what you eat—and that applies to teeth” is a modification of a famous saying about body chemistry. One of the important atoms in organisms is oxygen (O), which is part of water (H2O). Oxygen has two naturally occurring variants called isotopes; they have the same chemical properties but different weights because their nuclei have different numbers of neutrons. Both isotopes of O are incorporated into the bodies of animals that consume the isotopes in water and food.
The hard surface of teeth, called enamel, is made up largely of calcium phosphate, which contains oxygen atoms. The iso-topic composition of the oxygen in enamel varies depending on where an animal was living when the enamel was made. When water evaporates from the ocean, it forms clouds that move inland and release rain. Water with the heavier isotope of O is heavier, and tends to fall more readily than water containing the lighter isotope. As a result, regions of the world that are closer to the ocean receive rain containing more heavy water than do regions farther away, and these differences are reflected in the bodies of animals that dwell in these regions.
This property has been used to reveal an astounding fact about dinosaurs that lived in the great basins of southwestern North America about 150 million years ago. Camarasaurus was big—up to 25 meters long and weighing up to 45 metric tons. Henry Ficke from Colorado College analyzed the oxygen isotopes in the enamel of Camarasaurus fossils and found two kinds of teeth: Some had the heavy oxygen content typical of rains and rocks in the basin region. But others, surprisingly, had a lower proportion of heavy oxygen, indicating that these animals had lived at higher elevations 300 km to the west. This indicated for the first time that dinosaurs migrated a long way from west to east. The reason for this migration is not clear. Camarasaurus ate a plant-based diet, and perhaps the migration was directed at finding food.
Many biological phenomena are analyzed and understood in the context of chemistry. You will learn, for example, that adding even one atom to a large molecule can change its character and function. Analyzing the isotopes in dinosaur teeth is but one example of how chemical analysis has led to advances in biological science.
What insights into biological systems have been discovered through isotope analysis?
