THE LONG VIEW
At the January JMM in San Diego Kevin Robinson, a geologist at San Diego State University, spoke to the EM SIG about the local geology. He teaches about 500 students each semester in a course "Natural Disasters," but prefers to teach "Rock Types and Plate Tectonics." He took us on a beautiful trip where we saw many types of rock formations and were awed by the beauty of them. We took a bus down the Rose Canyon fault; many CA freeways are built along faults. In the 1960's many houses were unknowingly built on cracks and have had to been remediated.

First, Dr. Robinson told us some history. About 4.5 billion years ago the earth was becoming recognizably a planet, as opposed to a swirling glob of gasses. About 4 billion years ago most of the surface was covered with water, but a few islands of land were peaking through. It is now possible to stand on land that is 4 billion years old. These islands probably made up less than five percent of the earth's surface, but they gradually accumulated to become continental crusts.

By 3 billion years ago fairly large continents were beginning, but the continental plates have moved considerably since then. By 2 billion years ago the land area of the earth was about 20% of its total surface. The size of North America has doubled in the past 35 MILLION years.

About 500 million years ago, California, Oregon, Nevada, and Utah were still under the ocean. From 500 to 200 million years ago sedimentary rocks accumulated along the western edge of North America. Most of California wasn't here yet. Much has been deposited in the past 100 million years. Large parts of California were formed from 120 to 90 million years ago by intrusion of igneous rocks like those of the Sierra Nevada in an ancient volcanic mountain range which has since been eroded. However, the San Diego coastal plain has been uplifted only in the past 800,000 years.

Water lowers the melting point of hot rock, and volcanoes have pushed igneous rocks up from below. There were mountain ranges in CA similar to the Andes about 100 million years ago, but they were mostly eroded away in 50 million years. Now CA near the ocean is largely made up of sedimentary rocks, where much organic matter grew 20-6 million years ago. There are large basins of oil off the CA coast, and an off-shore oil drilling ban in CA.

The San Andreas fault system is about six million years old. It began when the Pacific plate hit North America. There are some geothermal power plants along the fault. "The energy available from geothermal is incredible." If the San Andreas fault broke, it would cause an earthquake similar to that in Indonesia in 2004. Alaska is considered the "catchers' mitt" of rumbles from slip faults along the western edge of North America. The last serious fault break was in 1847, and there has been about 150-year intervals between serious breaks. Between breaks there are smaller earthquakes and "creeping faults," which don't give quakes. One of the events that convinced geologists that continental drift was real was the Alaskan earthquake of 1964, which was just what the believers in continental drift had predicted.

The sea level has risen and fallen about 400 feet dozens of times over the past several million years as the global ice accumulates during ice ages and as it melts, dumps water into the ocean. Over the past 1.2 million years this has happened about every 100 thousand years. Before that, starting about 3 million years ago, ice ages happened about every 40,000 years. The ice ages have become more extreme over the past million years.

Homo sapiens sapiens emerged about 160,000 years ago, so we have witnessed and survived one ice age.