A Short History of Nearly Everything: Part IV

They spent one week each month at the Palomar Observatory in California looking for objects, asteroids primarily, whose trajectories carried them across Earth’s orbit

By this time, too, astrophysics had moved on so much that few astronomers wanted to devote their lives to anything as mundane as rocky planetoids.

Even if every asteroid in the solar system had a name and known orbit no one could say what perturbations might send any of them hurtling toward us. We can’t forecast rock disturbances on our own surface.

Altogether it is thought — though it is really only a guess, based on extrapolating from cratering rates on the Moon — that some two thousand asteroids big enough to imperil civilized existence regularly cross our orbit.

Every year the Earth accumulates some thirty thousand metric tons of "cosmic spherules" — space dust in plainer language — which would be quite a lot if you swept it into one pile, but is infinitesimal when spread across the globe.

So when, in the first week of 1980, at a meeting of the American Association for the Advancement of Science, the Alvarezes announced their belief that the dinosaur extinction had not taken place over millions of years as part of some slow inexorable process, but suddenly in a single explosive event, it shouldn’t have come as a shock.

I remember harboring some strong initial doubts about the efficacy of such an event.

Then in 1906, an Irish geologist named R. D. Oldham, while examining some seismograph readings from an earthquake in Guatemala, noticed that certain shock waves had penetrated to a point deep within the Earth and then bounced off at an angle, as if they had encountered some kind of barrier.

And because they come from a much greater depth, they tend to propagate over much wider areas.

Scientists are generally agreed that the world beneath us is composed of four layers — rocky outer crust, a mantle of hot, viscous rock, a liquid outer core, and a solid inner core.

He died of cancer in 1991, but shortly before his death he "lashed out at his critics in a polemic in an Australian earth science journal that charged them with perpetuating myths," according to a report in Earth magazine in 1998.

In particular what he couldn’t find was a structure known as a caldera.

The biggest blast in recent times was that of Krakatau in Indonesia in August 1883, which made a bang that reverberated around the world for nine days, and made water slosh as far away as the English Channel.

"It looks completely innocuous," he said. "It’s just a big pond. But this big hole didn’t used to be here. At some time in the last fifteen thousand years this blew in a really big way. You’d have had several tens of millions of tons of earth and rock and superheated water blowing out at hypersonic speeds.

Emerald Pool, remarkably, was all these things, yet at least two types of living things, Sulpholobus acidocaldarius and Thermophilus aquaticus as they became known, found it congenial.