Peter Zeitler told about a bit of cleverness I didn't realize before. Plagioclase has long been thought less than ideal for potassium-argon dating, because the argon part tends to leak from the mineral at high temperatures. But now that we have other ways to date plagioclase-bearing rocks, that flaw has been turned around. Because plagioclase securely retains argon only below about 300º C, the method becomes useful for dating when a rock has cooled to that temperature. And the uranium-lead method, once considered useless for the mineral apatite because of helium loss, is now used for dating when a rock cooled below about 70º C. What was noise has become a signal.
Then I went to a session on evidence of historic and ancient volcanic eruptions, whether in ice cores or human records. The most entertaining talk was by Ken Wohletz on the Dark Ages eruption (learn more about that on the PBS "Secrets of the Dead" series). Basically, the great Krakatau eruption of 1883 was just a pimple on the rim of an enormous caldera that blew up in the year 535, creating the Sunda Strait between Java and Sumatra and plunging the whole world into several years of cold and darkness. And one of my favorite speakers, Kevin Pang, presented what he does every year—stories of ancient eruptions extracted from the records of imperial China. He documented severe eruptions around the year 190 and claimed to find physical traces of them in the Greenland ice cores.
I made sure to cross the hall for a talk by David Stevenson, who thinks about the formation of planets as easily as a juggler keeps five balls in the air. His subject was the four Galilean moons of Jupiter and the puzzles they pose. He suggested that Io, Europa, Ganymede and Callisto have not always been where they are. For instance, Io (as I've explained) is in a place where its buildup of heat "is blasting it to hell," he said. Thus it would not have been able to form where it is today.
All four satellites, he said, appear to be spinning closer to Jupiter with time. During that time Ganymede could have passed through the same sort of gravitational resonant that is heating Io and Europa today. Only Callisto has avoided this tidal heating, and he called that an important clue to how Jupiter and its satellites formed. It was not just a miniature version of the sun and planets but a "starved disk" model that allowed the moons to form slowly without melting.
The audience hung on every word and peppered Stevenson with questions. "For a million dollars," one man asked, "where would you expect to find life—Europa, Ganymede, Callisto, or other?" He grinned and shouted, "OTHER!"
In the afternoon I sat in on a press conference and then toured the posters. Scientific press conferences are not like the President's—there are usually no cameras, just a few scientists at one table and reporters at other tables. The subject was the sunken city of Herakleion, recently discovered off the coast of Egypt where it sank during an earthquake, it's thought, in the years around 720. There's a TV special in the works, and a big session about it tomorrow.
Poster sessions are in a huge hall filled with aisles of partitions, covered with large presentations. Each poster has a sign telling what time the author will be standing there. Here are some of the cool posters I saw today.
- Tidal forces from the Moon seem to drag the Earth's continents westward.
- A database for the remote Siberian impact crater El'gygytgyn is allowing researchers anywhere to do "flythroughs" using satellite imagery.
- A 1998 expedition to El'gygytgyn recovered a sediment core that records Siberian climate for the last 400,000 years.
- College teachers send their students around the Web as part of their lessons, with good results. (Didn't see my site, though.)
- Quake Trackers lets school kids do real seismology on the Web.
- Rice University is producing a huge educational effort at earth.rice.educalled Public Connection.
- Large volcanic eruptions into and onto carbonate rocks could cause catastrophic global warming.
Finally, I went to the Honors Ceremony, in the ballroom of the Hilton, and watched several people get medals and awards. The first was a reporter, Richard Hill of the Oregonian. One of us!
