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For centuries, we’ve been mapping the surface of the earth, but what about what lies beneath? I’m Jim Metzner and this is the Pulse of the Planet. James Mungall is a geology professor at the University of Toronto. He says geologists string together different kinds of information to get a picture of the earth underground.

“When a geologist makes a map, he takes some kind of a base map maybe it’s a map produced by a forestry service, or it might be an air photograph and he or she goes out in the field and visits outcrops of rock and records on the map where each outcrop occurs. And then, you try to develop a pattern. You try to see where the different rock types occur, and you draw lines connecting them so that you can get a picture of the structure of the Earth. Then, either using diamond drilling information, or geophysical data, which lets us look into the ground, we try to infer what’s going on at depth.”

“The kind of research that I do usually involves going into the field and spending a considerable amount of time mapping first. I go and visit outcrops of rock, I record what rock types are present on those outcrops, and I also look at the outcrop scale of the structures that are there. How one layer of sediment or one igneous intrusion is related to other features around it. I collect samples, and then I bring the samples back to the lab. And I have microscope slides cut from the rocks, which are wafer-thin slices of rock mounted on glass slides that I can look at in a microscope. And that allows me to look at the microscopic textures and the compositions of minerals using an instrument called an electron microprobe. And we also take those samples, and we grind them up into powder and have them analyzed by a whole variety of methods to see what their compositions are.”

We’ll hear more about geology in future programs. Pulse of the Planet is presented by the National Science Foundation. I’m Jim Metzner.