GEOLOGY 1

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You CAN squeeze water from rocks

Squeezing rocks with a tiny diamond-tipped anvil at 3.7 million PSI makes water seep out, suggesting water 400 miles inside Earth's mantle lubricate fault surfaces and tectonic plates slide past each other explains surface earthquakes. How does water exist there in the first place with tremendous pressure and temperature quickly vaporizing it? Ocean water maybe seeps down into the porous lithosphere, just below Earth's outer crust. When ocean plates ram into continental plates this waterlogged lithosphere plunges into the mantle. While most of the water evaporates at high temperatures some reacts with rocks to form water-bearing minerals like serpentine, 13% water by weight. Serpentine lodged in chunks of lithosphere, insulated from the mantle's heat, sinks deeper. At high temperatures squeezing serpentine at 735,000 PSI equals depths of 100 miles. At lower temperatures serpentine insulated in blocks of lithosphere retained its water at pressures 5 times greater, equaling depths of 400 miles. Serpentine can sink into the lower mantle and be trapped. Here it warms up, releasing its water. Over 4 million trillion tons of water may be in the mantle. Accounting for barely .1% of the mantle's mass, its effect is enormous. Experiments at relatively low pressures show free water activates faults by decreasing fault surface friction.

Detecting Gravity Waves

Einstein said space is constantly squeezed and stretched by traveling waves of warped space. Gravity waves emanate like pond ripples through the universe from violent phenomena e g exploding stars, collisions between black holes or between dense, massive, burned-out neutron stars and other cosmic cataclysms. Sprawling $350 million gravity wave catchers Laser Interferometric Gravity-Wave Observatory (LIGO) identical L-shaped structures, one in Louisiana between Baton Rouge and New Orleans, the other near Hanford WA, have 2-mile-long arms stretching at right angles across flat, desolate ground longer than 40 football fields. Patterns of waves caught would reveal more about black holes and the universe's origin. Even as theoretical entities gravity waves inspired years of study. What would they look like? It's 2 years of fine-tuning before gravity waves register in either detector, not an experiment but a new kind of telescope opening a previously opaque window into the cosmos, imaging a whole different universe. Radio antennas, X- and gamma-ray satellites and infrared detectors reveal phenomena invisible to ordinary telescopes. Gravity waves are among the universe's most subtle phenomena. Even the biggest waves reaching Earth expand and contract space less than the diameter of an atomic nucleus. LIGO's designers think they can measure it.

Black holes collide frequently. Crowded star clusters, meeting places for stars and black holes, bring pairs close enough to capture each other in orbit and slowly spiral together. Black holes meet every million years in the Milky Way. LIGO catching waves from a region encompassing several million galaxies would detect black hole collisions every year. In 1917 Einstein published his general theory of relativity. At first physicists tried to detect Einstein's waves in metal bars interspersed with special crystals generating electricity when squeezed. Bar detectors never achieved needed sensitivity. Late 1970s, LIGO's first visions: Mirrors suspended near the ends of the arms move closer together and farther apart when gravity waves pass through. Lasers beamed up and down the arms measure even the slightest deviation in distance. The problem is even a monster gravity wave would move the mirrors less than the diameter of an atomic nucleus, trillionths of a trillionth of an inch. The mirrors must be as perfectly still as physics laws allow. Even a few air molecules could nudge the mirrors enough to ruin the experiment. The vacuum system alone cost $85 million. Designers also protect delicate LIGO from random seismic activity, passing trucks, landing airplanes and other disturbances. Only a gravity wave should move these mirrors. Black holes are by definition invisible, their gravity so powerful even light can't escape. Gravity waves know no such bounds. They're free to escape with a message about the structure of the black hole, real signatures of black holes, mapping the space-time curvature around a black hole. Black holes are not matter but pure space-time curvature, like a dent or bump in the fabric of space. Although telescopes seeing millions of light-years into space see millions of years back in time the early universe is shrouded from view of any instrument sensitive to light.

Tide cycle factors in global warming

Natural fluctuation in ocean tide strength over centuries may contribute to global warming. 1,800-year cycles of strong and weak tides coincide with climate change over the same period, letting us partly off the hook for rising temperatures caused partly by CO2 greenhouse buildup. Average global surface temperature rising 1 degree F since 1880 caused by increased CO2 from increased industry won't account for unusual preindustrial climate patterns e g a warming trend 500 - 1000 C E. Air cools when strong tides bring cold water from ocean depths to the surface. Weak tides mix the ocean less well, making warmer air. This cycle of weak and strong tides alternates over 1,800-year periods in response to alignment of Earth, sun and moon. There's also 90-year cycles of less profound change within the period. Existence of the cycles was already established but not the link between tides and global climate patterns. Today's warming trend began around 1500 and will continue another 400 years based on analyses of Greenland deep sea sediments and ice core samples offering geological data over tens of thousands of years. A warm period during the Roman Empire preceded a cold period devastating Greenland Viking settlements around 1100 and severe Northern European winters around 1300.

BAY TODAY, GONE TOMORROW

17,000 years ago the coast was 26 miles west, 6 miles past Farallon's peaks, with no San Francisco Bay for thousands of years. Today's bay's site was a series of broad valleys, each with a tributary stream pouring into a mighty, sediment-swollen river originating in the Sierra Nevada. It drained through the Central Valley, the Carquinez Strait, Raccoon Strait and the Golden Gate's stony ramparts. A bay is an anomaly for the San Francisco region. During the past 600,000 years the bay only existed during three brief periods totaling 15,000 years. Today's bay existed near its current size only the last 4,000 years. It should be around another 1,000 years.

5,000-YEAR LIFE-SPAN
San Francisco Bay's geological history is really the story of several bays, each lasting 5,000 years, and the tens of thousands of years between when the land supported big rivers and lovely valleys. It's about cataclysmic raising and lowering of the Pacific Ocean, stupendous volcanic eruptions, creation of mountains through grinding, compressing and upheaval of tectonic plates, and vast floods. It's also about life, of primeval cedar and pine forests, of Pleistocene mammoths and giant ground sloths, and of people hunting them with flint-tipped spears. Earth's features are geologically ephemeral.

NOTHING IS PERMANENT
Today's bay formed when the last ice age waned. At the height of the last glaciers 17,000 years ago large amounts of water evaporated from the oceans and fell as snow, not rain, compacting into huge continental glaciers. Sea level lowered 300 feet, exposing big expanses of today's continental shelf. As the glaciers retreated sea levels rose 3 - 15 feet per century. 10,000 years ago the ocean began sneaking through the Golden Gate, forming the nascent San Francisco Bay, reaching its present size within the last few centuries. While melting glaciers formed the bay sediments partially filled the subsiding basin it now occupies, making the bay half the size it would be. Sediment records indicate California's interior didn't always drain through the bay basin. Sierra Nevada minerals appeared in the basin less than 600,000 years ago, a blink in geological time. Before that, vast inland Corcoran Lake occupied much of the Central Valley, draining through the Salinas River into Monterey Bay.

VOLCANIC ERUPTION
760,000 years ago a tremendous volcanic eruption in Bishop created a great caldera depositing massive amounts of volcanic ejecta in the lake. This ash reached the bay when tectonic shift caused the Bay Area to subside and the lake's south end to rise 560,000 years ago, causing the lake to spill over the ridge separating it from the bay basin. The flow carved the Carquinez Strait and drained the lake, maybe happening so fast it was a single, catastrophic event, a great gush of water roaring to the sea. Since then tectonic upthrusting of Earth's crust plugged the Central Valley's outlet through the Salinas River. Now everything that flows into the Sacramento and San Joaquin valleys ultimately pours out the bay. Erupting Mount Lassen, smaller than the Long Valley Caldera near Bishop, also contributed sediments to the bay 435,000 years ago. Event sediments, Rockland Ash, are seen clearly in Fort Funston's sea cliffs on San Francisco's coast. As ice from the last glaciers melted the Sacramento and San Joaquin rivers became great, braided streams choked with sediment, dumping glacial outwash in the Central Valley and the Delta with so much sediment huge dune fields blew out of the river near Antioch 15,000 years ago. The same happened in Oakland, built over dune sand deposit called the Merritt Sand. There was no bay then but those sediments ultimately covered much of the bay basin.

SOURCES OF SILT
Fine silt and clay still come to the bay from the Sacramento-San Joaquin river system. The lion's share of sediment, mostly sand and gravel, issues from Alameda Creek, draining Livermore Valley through Niles Canyon. Ongoing bay sediment's biggest source is Livermore Valley. A huge alluvial fan of sediment deposited by Alameda Creek spreads under the bay from the Coyote Hills to Palo Alto's shore. Mountains built up the San Andreas and Hayward faults, sharply defining the estuary's limits. The process continues today with continued uplifting of the Santa Cruz Mountains straddling the San Andreas Fault. Simultaneously, land west of the Hayward Fault subsides. Meanwhile, structural rock underlying the South Bay slowly sinks and gradually tilts eastward. Ascending Santa Cruz Mountains and Berkeley Hills squeeze the Bay Block bedrock zone between them, basically fault-free at this point. As it continues to be compressed it might eventually develop new fault lines.

CHANGES CONTINUE
Dizzying change continues regardless of human activity. Erosion and plate tectonics grind on inexorably. Inevitable ice ages are triggered by perturbations in Earth's orbit, subtle movements caused by gravitational effects of Jupiter and the moon.

MASSIVE AMOUNTS OF DUST
Planets formed by sweeping up massive amounts of dust and debris when the solar system formed. Leftovers concentrate in a disk around the sun. Earth's orbital plane tips through this debris disk every 100,000 years or so. The dust occludes sunlight, reducing the amount of thermal energy reaching Earth's surface, probably not enough to start an ice age by itself. Oceans distribute solar energy globally but margins are very fine. Orbital parameters can't do it by themselves but they're triggers. When the balance is finally thrown off in the oceans, glaciation occurs quickly. Global warming? Couldn't ongoing atmospheric loading of heat-trapping gases like CO2 forestall another ice age and guarantee the bay's longevity, orbital wobbles notwithstanding? We should be cautious about releasing greenhouse gases but the orbital signal is too strong for them to overcome. Our distant descendants may forgo San Francisco bay views. When glaciation occurs the bay drains and we walk to the Farallones.

MAKING A BAY
3 geological processes shaped San Francisco Bay: rise and fall of sea level, shifting tectonic plates and deposited river sediment. All form an estuary that's in constant flux and that periodically disappears for tens of thousands of years.

Sea Level Rise
During the height of the last Ice Age 17,000 years ago sea level dropped 300 feet. West of what is now the Farallon Islands was dry land. Melting glaciers made sea levels rise. The current bay began to form 10,000 years ago, existing near its current size only for the last 4,000 years.

The Bay Block
Shifting tectonic blocks continue shaping the bay. The rising Santa Cruz Mountains and Berkeley Hills compress the Bay Block, a vast slab of Franciscan rock underlying the south bay and its sediments. Though the Bay Block is essentially fault-free it's expected this compression will ultimately form new faults.

CORCORAN LAKE
760,000 years ago much of California's Central Valley was freshwater inland sea Corcoran Lake. Its outlet, the Salinas River, drained to Monterey Bay. 560,000 years ago tectonic uplifting let the lake rise sufficiently to cut through the Bay Area's soft soils. The Carquinez Strait was rapidly carved. Uplifting also plugged the Salinas Valley outlet, leaving San Francisco Bay as the Central Valley's only outlet. Sediment deposited by Central Valley rivers limits the bay's size.

Geology Time Periods

3 eras Paleozoic, Mesozoic, Cenozoic, 11 periods mostly named for where rocks from the period were discovered. The 2 most recent periods divide into eras named in time sequence.