jamesteohart / svrid79 / Benny Marty / imaginasty / Mara008 / Wikimedia / Flickr / The Atlantic
The Atlantic has an interesting story about the evolution of whales. Whales have a strange history, from a dog-like creature to probably the largest animal ever on Earth. This article discusses the last 50 million years and how they travelled the oceans looking for food. During their journey, they had a few passengers - barnacles. It's these fossilized barnacles that are revealing new clues to the history of the whales.
“Essentially no one knows anything about whale migration in the prehistoric past,” says Taylor. “But the idea would be that as climate got more unstable in the last several million years—and we went through glacial maximums and minimums—the productive zones of the oceans would have been shifting around a lot, and these huge animals could quickly adapt their behavior to find these productive zones of the ocean. Evolution might have favored these really large animals that could migrate huge distances and survive off an enormous fat store.”
It’s an intuitive idea. But it’s long been just that—an idea. This is where Taylor’s humpback barnacles come in. The unassuming shells effectively act as a black box for whale journeys of the distant past.
Here’s the trick. Whale barnacles build their shells from seawater. Seawater, as you might imagine, is made of atoms. Some of those atoms are oxygen. And oxygen in the ocean comes in lighter and heavier isotopes. Water closer to the poles tends to be lighter because most of the heavier stuff—being heavier—has been literally rained out of the clouds in the long trip to the Arctic. This is because, in very general terms, the most evaporation happens where there’s the most sunshine (near the equator) and, as the water evaporates and moves pole-ward, it’s successively rained out, re-evaporated, rained out, re-evaporated, rained out and so on, along the journey north. In the process—with each step—the water is essentially distilled for lighter isotopes. As a result, animals swimming in the Arctic find themselves in lighter water.