A Moment of Science

DNA Dirt

How do biologist find DNA from organism that lived thousands of years ago? Find out on this Moment of Science: "DNA Dirt".

You may already know that DNA is a long molecule found in almost every cell in your body that contains your genetic blueprints. Encoded in the particular sequence of your DNA is a description of what kind of organism you are, how you work, and how to make more of you. DNA can be extracted from living things–run your fingernail along the inside of your cheek to harvest a DNA sample right now–or from dead remains. Now, it turns out DNA can also be extracted from the soil, even without a body anywhere near.

Researchers from the University of Copenhagen took a sediment core from a permafrost plain in Siberia. A “sediment core” is just a long, strait tube of earth. Imagine pushing a straw slowly into ice cream and then removing the straw: inside it would be a long thin ice cream sample. The surface of the earth is constantly covering itself over. With a sediment core, the lowest parts of the tube correspond to the oldest time period, while the highest parts are more recent.

The sample didn’t have any visible animal or plant remains in it, but researchers found loads of DNA anyway. They have already identified such animals as lemmings, bison, and –going way back– woolly mammoths.

But if there were no carcasses, how did the DNA get in the soil? That isn’t known, though some scientists speculate that animal dung contains enough stray cells to deposit DNA. That may mean a bison pooped here thousands of years ago, unknowingly dropping its genetic signature–just waiting for future biologists to dig it up again.

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