Most people know that the crust of the Earth is twenty-five or more miles thick under the continents, and that it would be rough drilling there. Many also know that under the oceans the crust is much thinner. It would be quite possible to drill there, into the top of the mantle, penetrating the Mohorovicic Discontinuity, however. They had talked about all kinds of data that could be picked up. Well, okay. But consider something else: sure, it's true that a sampling of the mantle would provide some answers to questions involving radioactivity and heat flow, geological structure and the age of the Earth. Working with natural materials, we would know boundaries, thicknesses of various layers within the crust; and we could check these against what we had learned from the seismic waves of earthquakes gone by. All that and more. A sample of the sediments would give us a complete record of the Earth's history, before man ever made the scene. But there is more involved than that, a lot more.

Another one? Martin asked me.

Yeah. Thanks.

If you study the International Union of Geology and Geophysics publication, Active Volcanoes of the World, and if you map out all those which are no longer active, you will note certain volcanic and seismic belts. There is the Ring of Fire surrounding the Pacific Ocean. Start along the Pacific coast of South America, and you can follow it up north through Chile, Ecuador, Colombia, Central America, Mexico, the western United States, Canada, and Alaska, then around and down through Kamchatka, the Kuriles, Japan, the Philippines, Indonesia, and New Zealand. Forgetting about the Mediterranean, there is also an area in the Atlantic, near Iceland.

We sat there.

I raised mine and took a sip.

There are over six hundred volcanoes in the world which could be classified as active, though actually they don't do much most of the time.