Europa has a thick crust of ice over an ocean. Lake Vostok, miles beneath the Antarctic ice, is similar. But lessons from one may not apply to the other. NASA image

It was a thrill to learn that on Sunday, Russian scientists managed to poke a drill tip through miles of Antarctic ice into Lake Vostok. Samples of water from this extreme environment promise to provide one of biology's severest tests of life on Earth. Scientists are talking up the possibility that this experiment, the first of several in progress in Antarctica, could tell us more about possible life on the icy satellite of Jupiter named Europa. Is that a stretch?

We're asking different questions here. At Vostok, we want to know if life has survived; at Europa we want to know if life could have arisen. In that context I think that Vostok and Europa are worlds apart; their similarities are superficial. Let's look at the two places in a bit more detail.

Lake Vostok is a large tectonic basin, rather like Lake Tahoe, that happened to be overrun some 15 million years ago by the growing Antarctic ice cap. It has been sealed in profound darkness and freezing cold ever since, with the ice flowing slowly over it. Here's a diagram of the situation.

National Science Foundation image

The lake is kept unfrozen because of a trickle of heat from the Earth's crust beneath plus the effect of great pressure in depressing the freezing point. Ice melts at the upstream end and lake water freezes at the downstream end, so on the geological time scale there's an exchange of water, and the water itself must be charged with air carried in by the ice. But the amount of minerals and nutrients entering the lake this way must be astronomically small. Somewhat larger amounts may come from the rock and sediment of the lake's floor, but the picture is still disheartening.

And yet we have found life everywhere on Earth, from temperatures above the boiling point to below freezing. Microbes are recovered from within the ice cap itself. I believe that the microbes originally sealed into Lake Vostok survive today, because that's the way to bet on this planet. However, from everything we know, life could never have arisen in such a place. The raw ingredients and energy required are absent.

Is that true for Europa? It's colder on its warmest day than anywhere on Earth, true. But Europa should have much more of the assets for life than Vostok.

Europa is an old world that formed along with the rest of the planets. Like Earth, Europa separated into a dense interior and a light shell, only with a greater share of water. Its rocks, like those of the early Earth, had lots of natural radioactivity that must have generated enough heat to keep part of the overlying water melted throughout its history. (More recently, Jupiter's four major satellites have fallen into mutually resonant orbits that wring them with changing tidal forces. The innermost moon, Io, is heated to volcanism this way, and Europa and Ganymede are heated to lesser extents.) The heat must have expressed itself in hydrothermal vents, too, exactly like Earth's seafloor "black smoker" vents.

In a word, as far as planetary scientists can tell Europa should have started out with the same setting that is commonly thought to have spawned life on Earth. The first structures that served as cell membranes could have arisen at hydrothermal vents, which would exist on Europa just as they do on Earth: springs of hot, chemically active water on the floor of a big cold sea. The water itself should contain ammonia, sulfates, even hydrocarbons. All of this is straightforward modeling based on what we already know about the solar system.

Model of the icy crust of Europa. Jet Propulsion Laboratory image

Planetary modelers are finding that the thick ice shell of Europa should have some interesting activity, too. The eerie striped pattern of Europa's surface shows that the ice fractures regularly due to tidal forces. When that happens, water would rise and its dissolved gases would come out in bubbles. These "Perrier ocean" eruptions would spray over the surface, where the ice and its organic compounds would bake and polymerize and react in the radiation from Jupiter and the Sun.

Eventually, after approximately a billion years, the entire icy crust would become replaced with ice bearing this baked material. And at that point you would have a nutrient cycle. In sum, it's quite plausible for life to arise and persist on Europa where it's quite impossible in Lake Vostok. If we ever get a spacecraft to Europa—proposals keep being submitted—our experience drilling to Vostok would help us drill through Europa's crust. But a more elegant proposal is to simply swoop over Europa in low orbit and scoop up bits of dust from its icy surface raised by micrometeorite impacts. Just like on Earth, if life is on Europa its signs should be everywhere.

A nodule of Napa Glass Mountain obsidian, etched by hydration during its long burial, reveals signs of its origin as a thick, sticky lava. Photos by Andrew Alden

The Napa Valley is an intriguing place even if wine doesn't interest you. Its very geography has an intangible personality. Running north-south, the valley is lit differently throughout the course of the day. It has the flat valley floor along the Napa River that you'd expect in a major agricultural region, but odd rocky hills are scattered about the valley with the irregularity of tossed pebbles. On behalf of Napa Valley winegrowers, geologists have studied the underlying soils and rocks, tracing from them a history of tectonic upheaval, recent volcanism and gigantic landslides.

The western side of the valley is the Mayacamas Mountains, here made up largely of marine sedimentary rocks of the Franciscan and Great Valley complexes (100 to 150 million years old). The eastern side is the Vaca Mountains, which consists mostly of much younger lavas of the Sonoma Volcanics (less than 5 m.y.). Here it is in a simplified geologic map.

The valley floor consists of recent sediments (Q) while young volcanics (T) and older sedimentary rocks line its sides. From USGS Scientific Investigations Map 2956.

Each set of rocks responds its own way to California climate and yields its own set of soils, and the floodplain between them mixes the two in different blends. Its wide range of soils and settings is part of what makes the Napa Valley such an endless playground for winegrowers. The same was true in prehistoric times, when the valley was a rich habitat for the Wappo and Patwin tribes and other peoples before them.

And this brings us to Napa Glass Mountain.

The natives made their cutting and scraping tools as needed, chipping them from stone of a few select kinds. The best toolstone is obsidian—a glasslike lava without crystals or bubbles that would mar the sharp edges and flat faces of an effective tool.

Obsidian is uncommon. To make it, a lava must have both a very high silica content and a low water content; it also helps to cool quickly. High-silica lava is classified as rhyolite and the Sonoma Volcanics field has plenty, but few rhyolites yield obsidian. Notable sources for the natives in this part of California were Annadel near Santa Rosa, Borax Lake near Clear Lake, and Napa Glass Mountain, which is just north of the town of St. Helena. Toolstone was an important trade item, and archaeologists map its distribution in ancient sites as clues to prehistoric commerce.

The Napa obsidian is a stone of a luscious pure black, and you can see it in a large roadcut on the Silverado Trail north of St. Helena at the narrowest point of the Napa River's floodplain. Here's a closeup geologic map.

Pinkish units are part of the Sonoma Volcanics (Tsa, Tsr, etc.), gray units are Franciscan rocks, units with "Q" are recent sediments. From USGS Scientific Investigations Map 2956.

The roadcut is just north of the intersection with Lodi Lane; you can park on either side of the road but be careful of traffic. The exposure is tall and shows the crude bedding of the mixed ash and lava beds, now highly weathered.

Obsidian occurs scattered in a whitish matrix in fractured lumps up to a meter long. The matrix may be altered material that was once obsidian, and/or it may consist of fine rhyolite ash—I have not studied it closely enough to hazard a guess. Parts of it may actually be perlite, a lightweight stone that forms where rhyolite reacts with internal water. Obsidian does not last long in the geologic record because its crystal-free substance is prone to attack by chemical weathering.

You don't need to dig into the cliffs; let other people who actually use obsidian do that risky operation. Instead, poke around your feet and look for bits like these.

The outsides are rough and coated with white hydration rinds, but inside they display their creamy texture and lustrous conchoidal fracture, the properties that make obsidian the ideal toolstone. Don't be greedy. And be ready to tell passers-by, like the curious police officer I spoke to during my last visit, what this cool place is all about.

More:
Obsidian photo gallery
Perlite
Rhyolite
Stone Tools

The Monticello Dam occupies Devils Gate, a deep cleft in the massive sandstones of the Great Valley Sequence. Photos by Andrew Alden

This outing visits two great landmarks of the northeastern Bay Area—one highly visible, the other well hidden. Both feature the same body of rock: the mighty Great Valley Sequence.

Most of Northern California's bedrock is part of just three large bodies: the granite of the Sierra, the metamorphic rocks of the Coast Range, and the sedimentary rocks of the Central Valley. All three are parts of one entity: a former subduction zone. Picture the Pacific seafloor plate being carried eastward against the North American continental plate and plunging underneath it—subduction. (That's the exact situation today in the Pacific Northwest, and along the whole west coast of South America.) The descending oceanic plate releases fluids into the continental plate above it, which generate magma and big chains of volcanoes. At the same time, the continent scrapes off pieces of the plunging oceanic plate like the bottom of an escalator gathers trash. The volcanoes quickly erode into sediment, which washes offshore in thick beds of sand, boulders and silt. The Sierra is the exposed roots of the volcano belt, the Franciscan Complex is the scraped-off stuff, and the Great Valley Sequence is the offshore sediment.

That all happened long ago, and since then the San Andreas fault has slowly ripped apart the neatly organized subduction zone. At the same time, pressure across the fault has pushed up the Coast Range and curled up the edge of the thick blanket of sedimentary rock in the Central Valley. The arrangement is still close to its original simplicity north of the Bay Area, as this map shows.

Modified from USGS Open-File Report 90-226

Below is a closer view of the setting for today's outing. The south end of that long ribbon of Great Valley Sequence rocks is the Vaca Mountains, and the highest part of the range is a sharp hogback called Blue Ridge.

From USGS map MF-2403, "Geologic Map of the Northeastern San Francisco Bay Region"

Mount Vaca is its highest point, at the west edge of the leftmost green ribbon to the left of the "i" in "Ridge." If you follow that geologic boundary north, it meets the dam that created Lake Berryessa, Monticello Dam.

Blue Ridge is a massive landmark wherever you are in the Napa County hills or the southern Sacramento Valley. It's high, long and straight. West of Winters its profile is interrupted by a big notch. This is the Berryessa water gap, carved by the waters of Putah Creek as the ridge rose across it.

You reach Mount Vaca by taking Pleasants Valley Road north from Fairfield. Two very steep roads go up the mountain, Gates Canyon and Mix Canyon roads. Take Mix Canyon Road (trust me, don't take Gates) and watch carefully for cyclists and descending vehicles. Soon you'll start seeing Great Valley rocks like this thick-bedded sandstone, tilted almost vertical. The sequence is estimated to be about 13 kilometers thick, representing some 80 million years of steady erosion of the Sierra highland into a nearby shallow sea (a foreland basin). The basin steadily sank from the load, like the Louisiana coast does under the sediment load from the Mississippi River.

The rocks grow younger from west (right) to east (left).

At the top of Gates, a spur marked "Private" goes left. Go ahead and take it to reach Mount Vaca. The right-hand way, Blue Ridge Road, is also highly scenic. Two-wheel drive is OK, but drive cautiously. The views from along the top of Blue Ridge are fantastic.

Mount Diablo from Blue Ridge.

Grapevines and Mount Tamalpais from Blue Ridge. At about 2600 feet, this may be the highest vineyard in California.

The ridgeline rocks are massively bedded sandstone of the Venado Formation, roughly 91 million years old. We'll get a better look at them next, at Devil's Gate.

Return down to Pleasants Valley Road and resume heading north. Notice the recent downcutting of the stream here. Turn west on state route 128 and head up the canyon of Putah Creek. Instead of climbing Blue Ridge, we're cutting through it. Devil's Gate is the deepest part of the canyon, where the stream crosses the Venado Formation, and the best spot to build the Monticello Dam.

On both sides of the dam, the Venado is beautifully exposed. This is the natural exposure on the far side of the dam. Roadcuts on the near side expose the Venado in real detail.

If Lake Berryessa is high, you may be treated to the sight of the dam's "Glory Hole" overflow structure, an endless circular waterfall that I photographed in action in May 2006.

To those who know rocks, this chondrite meteorite could not be mistaken for an Earthly stone. Photos by Andrew Alden

The other week I mentioned, in talking about concretions, that people can be fixated on the idea that they have found a dinosaur egg or meteorite. This last week meteorites featured in two news stories, one excitingly true and the other almost certainly bogus.

The exciting story was about a set of meteorites recovered in the desert of Morocco, a few months after their fall from space had been recorded. That doesn't happen very often—once meteors arrive in the atmosphere, their unguided trajectory means that a rather large area must be searched to find them. What was extraordinary was that these rocks were from Mars, certified as such this week by an expert scientific panel.

Meteorite hunting has become a cottage industry in the Sahara Desert, where conditions are ideal for space rocks to be preserved and for practiced observers to spot them. The locals who found the new Martian rocks sold them to dealers, who in turn marked up the price to almost a thousand dollars per gram even before the meteorites were formally certified as Martian.

Meteorites are most easily found in two places on Earth, the Sahara and Antarctica. In the case of Antarctica, they fall on the ice cap, where no other rocks exist at all. Movements of the ice can concentrate these meteorites, including the rarest stones from Mars and the Moon, in certain areas that are surveyed regularly and exclusively by scientists. That's good for science. For its part, the Sahara is good for the rest of us who can acquire these rarities for our own pleasure. And scientists can still study Saharan stones because meteorite hunters must donate pieces of their finds to a museum to qualify for authentication, without which the stones have no value. It's a tidy system with little impact on the environment.

The California deserts are also promising places for meteorite hunters. At least one Martian stone has already come from the Mojave. Meteorite hunting is simple in principle, yes, but far from a casual hobby. First you acquire a very intimate knowledge of the rocks that belong there, and then you examine approximately a million rocks to find one that doesn't belong there. And with that, you start to learn about meteorites. I love rocks inordinately, but I think I would still go mad. Dr. Randy Korotev is a genuine meteorite expert at Washington University who gets torrents of email from would-be meteorite finders. On his excellent "What to Do" page, he says that of over 2000 serious inquiries over the years, only eight people had real meteorites.

Easier to dream of fabulous wealth falling into your back yard. That dream, fed by an extremely rare handful of true stories, can blind people to the obvious. And that leads me to the Castro Valley man who got a reporter to feature his story in the San Jose Mercury News last week. His story did not even point to a meteorite, let alone prove it. He said he responded to his dog's barking and found a fresh pit in his back yard with a smoking, red-hot stone in it. That scenario is a old urban legend about meteorites that is never true. He said he talked to experts from Lawrence Livermore National Lab, who had him hold a magnet against the stone and try to cut off a piece of it. He claimed that after finding it both non-magnetic and hard enough to break a hacksaw blade, those experts told him that was positive evidence. None of that is what an expert would say. And the object he showed a photographer had a silvery color and finish (which could not be iron because it was non-magnetic), and a multiply-layered structure that is very common in Earth rocks. In short, it looked nothing like a fresh meteorite and everything like an ordinary metamorphic rock. But he was fervent enough in his belief to fool a reporter, and at least one editor, into running the story anyway.

This is the back side of the chondrite shown at the top. Note the dark fusion crust and the hollows, called regmaglypts, carved by erosion in passing through the Earth's atmosphere. And a magnet sticks to it because it has small grains of iron metal throughout it.

Easier to save up some of your birthday money and buy a nice little meteorite at a rock show from a large, well-run dealership. My advice is to wait until the afternoon of the last day for the best price; dealers hate to pack up their inventory. That's how I got my 1/3-pound chunk of meteoritic nickel-iron from the Sikhote-Alin fall. There's nothing like the feeling of this ancient space metal in your hand.

The Sikhote-Alin fall occurred in eastern Siberia in 1947. Specimens like this are readily available.

I've written more about Martian and lunar meteorites on my About.com site. I also have a photo gallery there. Dr. Tony Irving has a deep and erudite page on Martian meteorites.

Concretions at Bowling Ball Beach. Photo by portmanteaus under Creative Commons license.

My line of work brings various people to me, asking about a mineral object they have found. Often that object is a rounded shape of ordinary-looking sedimentary material, cemented into stone. "It's a very nice concretion," I inform them. A concretion is not as exciting as what they hoped it might be—a fossil egg is their fondest wish, followed by a meteorite—but concretions can be sources of wonder and even inspiration, if not money.

"What is this thing in the rock?" may be the oldest question in geology. It was, at least, the subject of geology's founding document, a short treatise published in 1669 by Nicolaus Steno on "solids naturally embedded in solids" better known by the first word of its long Latin title, "Prodromus." It took strenuous reasoning and airtight argument for Steno to establish today's common-sense knowledge that most "solids in solids" are either fossils, large sedimentary particles, or mineral crystals of some kind. (Steno's birthday was observed yesterday with a "Google doodle.")

Concretions aren't any one of those three possibilities, but a confusing mixture: hard and symmetrical like a crystal, granular like a sedimentary stone, round and organized-looking like a fossil. They look as if they actually grew inside solid rock. And so they did, sort of. They appear to have formed rather early in the process that turns buried sediment into rock, as mineral cement is deposited in layers growing outward from a central point—or perhaps resisting a cementation process advancing inward upon them instead. The grains of sediment were undisturbed; only the cementing mineral, usually calcite or iron oxides, moved in to fix them in place.

It can be hard to tell how a concretion might have formed. Some are stony lumps with a fossil or a mineral particle inside, where it's plausible that some chemical mechanism arising from the central object controlled things. Some have fractures inside, filled with crystals. Others, like this concretion I found in the hills of Oakland, have nothing in particular at their core, just pure clay or sand. Geologists find concretions only slightly less puzzling than the general public.

While fossil eggs aren't documented in the Bay Area (no dinosaurs at all, in fact) and meteorites aren't either, you may spot concretions wherever sandstone or shale crops out. The biggest ones I know of are in Mendocino County at Schooner Gulch State Beach near Point Arena, where the stretch north of Gallaway is called Bowling Ball Beach. That's it at the top of this post. There are large ones, less well formed, at Fitzgerald Marine Preserve that I showed here a few weeks back.

Concretions can take many shapes. (I have a gallery of them on About.com.) In the Imperial Valley on the Mexican border, a site west of Calexico near the iconic mountain El Centinela (Mount Signal) yielded "sand spikes," concretions the shape of a whole clove. Most of them had their long tips pointed west. In 2000, they inspired artist Allan McCollum to make them the basis of a large art project, "Sand Spikes from Mount Signal." The signature image was a five-meter replica and a hundred life-size copies of one of these curious solids within a solid.

This solid vein of white mineral near Endeavour crater, up to 2 centimeters thick, has every appearance of the well-known mineral gypsum. NASA/JPL-Caltech/Cornell/ASU image.

We have been studying Mars with spacecraft for almost 40 years now, starting with fly-bys and progressing to landers and then rovers. Each of these scientific missions has been more ambitious than the one before, and each has found more and more Earth-like features on Mars. The latest example was announced last month in San Francisco at the annual AGU meeting: Mars has veins of gypsum. I've seen gypsum veins myself, right here in California. And you can too.

The currently operating Mars rover is named Opportunity, and it has managed to roll across the pristine Martian ground for more than 33 kilometers since it landed in 2004. Nosing around the rampart of the crater Endeavour in a monotonous area of basalt rock, Opportunity came upon the vein of solid bone-white mineral shown above. It approached closer and turned its alpha particle X-ray spectrometer on the stuff, along with its close-up camera. The spectrometer indicated sulfur and calcium in the right proportions, and the camera images reminded NASA scientists of nothing but gypsum, hydrated calcium sulfate or CaSO₄·2H₂O.

Close-up of the Martian gypsum vein. NASA/JPL-Caltech/Cornell/ASU image.

All right, so what? Well, gypsum points directly and unmistakably to liquid water, something that we've been looking for on Mars but never quite proving. There is gypsum-like dust blowing around parts of Mars, like it does at White Sands in New Mexico, but no sign of its origin. The mission's chief scientist, Steve Squyres, said at the AGU press conference, "This stuff was formed right here. There was a fracture in the rock, water flowed through it, gypsum was precipitated from the water. End of story. Okay, there is no ambiguity about this. This is what makes it so cool. . . . Here the chemistry and mineralogy of it just scream of water."

On Earth, gypsum is found in two main settings: wherever seawater begins to dry up, gypsum comes out of solution first and can accumulate in thick beds. And wherever hot-spring type fluids concentrate dissolved matter, gypsum is a likely mineral. The Martian vein appears to be of the latter, hydrothermal type. California's Central Valley, for much of recent geologic time, has been the former type of setting—a shallow sea basin or brackish lake.

Gypsum is especially abundant in the Kettleman Hills, an area of former Central Valley seabed that has been gently lifted by recent tectonic activity. If you have an extra hour next time you're on Interstate 5 going to Los Angeles, turn off at 25th Avenue, south of Kettleman City, and pull over once you enter the hills. Gypsum litters the ground there, and farther south near Lost Hills gypsum is being mined to make drywall, soil additives and plaster of Paris.

Gypsum of the Kettleman Hills. Photo by Andrew Alden.

If you're there in nice weather, enjoy the scene and think of Mars. Maybe you'll share the tantalizing feeling that the discovery of Martian gypsum arouses in geologists despite their best mental effort.

Kettleman Hills, 26 May 2010. Photo by Andrew Alden.

Endeavour crater, Mars, 6 August 2011. NASA/JPL-Caltech/Cornell/ASU image.

Like one of those 1950s-vintage Cuban taxis, Opportunity has hung on far longer than people originally planned. Planetary space missions have a fairly short "prime mission" of a few months or maybe a year, but everyone knows without admitting it that the rugged, overdesigned machinery will last a lot longer. NASA makes a big deal out of extending the mission, a year or so at a time, and we all feel good about getting our money's worth. In the case of Opportunity, its prime mission began eight years ago and the solar-powered contraption is still plugging along. Imagine what its successor, the rover Curiosity, might do once it lands in Gale crater in August of this year.

Read more about the discovery from NASA.

Do you have a unique voice that sets you apart from the crowd? Contribute your stories to QUEST!

KQED QUEST is looking to add new voices to our blog, which already offers commentary from our producers, reporters, and local writers from our partner institutions at Chabot Space & Science Center and The Tech Museum.

We're looking to include folks who are actively involved in the science, environment and nature blogging community – e.g. have a blog, guest post on others' site, and comment / participate in relevant discussions. And we're looking locally. Our blog has a strong SF Bay Area focus, though we do occasionally cover and/or perform analysis on how this stuff elsewhere that affects the Bay Area.

What we cover

QUEST’s geographic coverage is from Mendocino to Monterey and from Sacramento to Santa Clara, and generally covers 9 content areas: astronomy, biology, chemistry, engineering, environment, geology, health, physics and weather.

Requirements

• Original posts, 3-500 words with at least 1 image. Schedule determined on availability, but weekly or bi-monthly is preferred.
• Posts should relate back to at least one of our 9 themes for the program: Astronomy, Chemistry, Engineering, Physics, Weather, Geology, Biology, Environment, Health.
• Topic should be something about which you have some expertise and/or passion.
• A unique voice and ability to follow our QUEST writing guidelines (see below).
• Experience with WordPress or similar blogging platform.
• Willingness to occasionally be assigned a post topic by the editor as current events dictate.
• Respect for copyright and fair use.

Would I get paid?

Yes – we offer a small stipend on a per post basis.

Alrighty, then. How do I apply?

Email us a note and bio to questeditor@kqed.org explaining what you'd like to write for us. Please also include some links to relevant blogs you admire, and/or participate in, and why. Send us a writing sample or two (links are fine), and we'll review it in the next couple weeks. Last day to submit is February 1st. Our hope is to bring aboard a few new bloggers by mid-February.

Some beats we're interested in

Although we want to hear from a wide range of writers, here are a few coverage areas we're keen on in particular:

• Bay ecology background and issues
• Science education
• Silicon Valley / engineering innovations
• Hacks, DIY, and hands-on science activities
• Hiking and outdoors (with a science focus)
• Food science
• Convergence of art & science
• Nature & science photography

Writing Guidelines

(As laid out by our managing editor, Paul Rogers)

Why does my grandmother care? A key requirement of QUEST bloggers will be to explain scientific and environmental issues in a way that the general public can understand. Our audience is mostly made up of people who aren’t scientists or environmental activists. Posts should explain why the topics they are writing about are relevant to Bay Area residents.

Get to the point. Studies have shown that readers spend only a minute or two on most web sites before moving on. The average reader reads about 200 words a minute. Write tight, and lively. Keep it interesting and informative.

Avoid jargon. The purpose of good writing is to communicate clearly. Don’t use complex, esoteric scientific terms. Instead of saying "non-point source pollution," say "polluted runoff." Instead of "extravehicular activity," say “space walk.”

Be personal. Relate personal experiences. Speak in the first person. Tell them where you saw the blue herons or which movie best depicts what a real moon base might look like. Find your own voice and write in a compelling, approachable way.

Be passionate. Write about subjects and topics that you care about. Please don’t feel you have to stick to a script or formula. Express yourself.

Drive traffic to the blog. Place a link in your correspondence and comments to the blog. Mention it on other web forums.

Write for the bigger picture. Don’t view the blog as a place just to promote your institution or pet cause. Keep in mind your audience is made up of a wide diversity of people, with wide interests.

Speak your mind, but check your facts. Or your audience will do it for you with painful results.

Know your fellow bloggers. You'll be part of a vibrant community with fresh ideas and discussions nearly every day. Don't be afraid to comment on their posts, or link to their entries. Have fun with it! Dreary bloggers or insufferable policy wonks need not apply.

The next time you go to the beach, whether at the ocean or beside a river, take a closer look at the sand and think about the stories those grains can tell!

Sand . . . we play in it, we stroll on it, we make castles out of it, but what do we really know about it?

Most people use the term “sand” to refer to loose material on a beach, but sand is actually a grain size measurement used by geologists to describe sediments varying in size from about 1/16 mm to 2 mm in diameter. Sand can be found not only along ocean beaches, but along flowing rivers and beside land-locked lakes.

Mineral and volcanic sands are terrigenous, meaning that they come from the land. Mineral sands start as mountains and boulders and are gradually broken into smaller and smaller particles by weathering and erosion. Being alternately heated and cooled through the seasons, rolling and tumbling around in mountain streams and rivers, rocks are broken apart by the water’s movement. The black sand beaches of some islands (e.g. Hawai’i) are volcanic in origin. Lava rocks, chunks of cooled molten lava, are broken down into sand over time by physical and chemical weathering.

Some sand is biogenous, meaning that it comes from living things, such as mollusk shells and corals. The energy from water breaks shells down into tiny pieces that eventually are washed onto beaches. Parrotfish in the tropics use their teeth to scrape off and grind down bits of coral reefs; the undigested particles pass through the fishes’ digestive systems and end up as sand on tropical beaches!

If you examine the beauty of beach sand with a magnifying glass, the shape, size, and color of the sand grains can tell many stories.

Shape indicates the age of sand grains. Different materials break down at different rates. For example, quartz is very sturdy and takes longer to become sand than the calcium carbonate material of mollusk shells. Younger sand has sharp and angled edges; it needs time and wave action to become rounded. Sand particles that are smooth and well-rounded are evidence that they have been rolled around for awhile.

Wave action is the story told with grain size. The story is simple: small waves move small sand grains around; large waves move large grains. In addition, Aeolian transport, or sand movement driven by winds, shifts the sand around on the beach, shaping and reshaping, covering and uncovering.

Color offers evidence for source materials – sand particles that are clear, tan, gray, or brown might be quartz or feldspar, black or gray particles could be ilmenite (titanium oxide) or magnetite (iron oxide); garnets are red, mica is silvery black or gray, and shells are purple, white, black, or brown.
The chorus from the song “Mountain in my Hand” (on the Only One Ocean CD by the Banana Slug String Band) explains it best:

“I’ve got a mountain in my hand from the rain-washed land; down by the sea now is where I stand, with this mountain in my hand trying to understand; Oh, oh, wonderful sand.”

Additional Links

• Sea Grant North Carolina

You know Mount Diablo. But do you know what kind of rock it's made of? Photo by Andrew Alden

If you're like me, one highlight of your Christmas celebration is the consternating quiz that columnist Jon Carroll publishes in the San Francisco Chronicle every year. Acknowledging the greatness as well as the priority of the Carroll quiz, I am humbly pleased to bring a geological version to the pages of KQED Quest Science Blogs. The quiz is centered on the Bay Area, which in addition to its other virtues is a premier destination for Earth scientists.

There are 20 questions, each with one correct answer. Some answers may be found in my posts from this year. Some answers can be found on Google and others cannot, but you're coolest if you don't need to search. There is one big hint on this page.

And now the fine print: No prizes are awarded; answers will be added to this post on Boxing Day; until then please post questions, not answers, in the comments. All right? OK!

1. What is California's state rock: gold, mariposite, quartz, serpentine?

2. How big was the 1906 San Francisco earthquake: 7.8, 8.0, 8.2, 9.0?

3. Which of these places is on the North American plate: Aptos, Bolinas, Colma, Davenport?

4. Which of these places is on the Pacific plate: San Francisco, San Jose, Santa Clara, Santa Cruz?

5. What is the highest magnitude earthquake that the Hayward fault is capable of: 6.7, 7.0, 7.5, 8.0?

6. Mount Tamalpais is primarily what rock type: blueschist, chert, marble, melange?

7. What mineral resource has NOT been produced in the Bay Area: coal, mercury, petroleum, uranium?

8. What fossils are NOT found in the Bay Area: ammonites, dinosaurs, hypsodonts, mammoths?

9. What fault continues north where the Hayward fault ends: Calaveras, Rodgers Creek, San Andreas, Zayante?

10. Mount Hamilton is primarily what rock type: gneiss, granite, graywacke, greenstone?

11. What fault continues north where the Concord fault ends: Flint Hills, Green Valley, Greenville, Maacama?

12. Which Spanish word tells you there was once a lime kiln here: calabaza, calavera, calera, calesitas?

13. The San Gregorio fault occurs onshore in what county?

14. Franciscan rocks are mapped in 14 different entities called what: belts, formations, melanges, terranes?

15. What rock type is at the top of Mount Diablo: basalt, harzburgite, rhyolite, schist?

16. Which entity allows personal fossil collecting: BLM, Caltrans, Coastal Commission, state parks?

17. Which North Bay mountain is an actual (former) volcano: Burdell, Konocti, St. Helena, Tamalpais?

18. Mount St. Helena is primarily what rock type: diatomite, serpentinite, slate, tuff?

19. What kind of ore was mined south of Livermore during World War II: iron, magnesium, uranium, vanadium?

20. Where is the Bay Area's only geyser: Calistoga, The Geysers, Great America Park, Mount Diablo?

And here are the answers:

1. California's state rock is serpentine, better known as serpentinite.

2. The 1906 San Francisco earthquake was magnitude 7.8.

3. Colma is east of the San Andreas fault and therefore on the North American plate.

4. Santa Cruz, conversely, is on the Pacific plate.

5. The Hayward fault is considered capable of a magnitude 7.5 earthquake.

6. Mount Tamalpais is primarily melange, an intimate mixture of metamorphic rocks.

7. To my knowledge, uranium has never been produced in the Bay Area.

8. No dinosaur fossils are known from the Bay Area.

9. The Rodgers Creek fault continues north where the Hayward fault ends.

10. Mount Hamilton is primarily graywacke, a variety of sandstone.

11. The Green Valley fault continues north where the Concord fault ends.

12. "Calera" is the Spanish term for a limekiln, where limestone is roasted into lime. You may now look up the other three words.

13. The San Gregorio fault occurs onshore only in San Mateo County, just missing San Francisco and Santa Cruz counties.

14. Franciscan rocks are mapped in 14 different entities called terranes.

15. The top of Mount Diablo consists mostly of basalt.

16. The Bureau of Land Management allows personal fossil collecting on the public lands it administers.

17. Mount Konocti, overlooking Clear Lake, is a former volcano, although the others contain volcanic rocks.

18. Mount St. Helena is primarily tuff, or volcanic sediments.

19. Magnesium ore, the mineral magnesite, was mined in the ultramafic rocks south of Livermore during World War II.

20. The Bay Area's only geyser is in Calistoga, but it's an artificial one that erupts in a drilled hole.

From hackerspaces to banana slugs, flying telescopes to cheese — it's been a quite a diverse year of storytelling here at QUEST. Here's a round-up of the top 10 video and audio stories and blog posts (based on page views) that you've enjoyed from the past year. Please let us know what other stories you've enjoyed in the comments section below, and if there's anything you'd like to see in the coming season!



VIDEO:

Nanotechnology Takes Off

Stem Cell Gold Rush
Science on the SPOT: Banana Slugs Unpeeled
Berkeley Lab Physicist Shares Nobel
Science on the SPOT: Open Source Creativity – Hackerspaces
Super Laser at the National Ignition Facility
The World's Most Powerful Microscope
The Science & Art of Cheese
Mt. Umunhum: Return to the Summit
The Fierce Humboldt Squid

AUDIO:

Up All Night on NASA's Flying Telescope</a>

The Lost Lagoon
Energy-Saving Windows Get Smarter
The Amazing Transformation of San Francisco's "Sludge Puddle"
Supercomputers Hit an Energy Wall
From Tunnel to Tap: Quake-Proofing Our Water Supply
"A Big, Captivating Idea": The Bay Area Ridge Trail
Architecture for the Birds
Gulls Threaten South Bay Salt Pond Restoration Work
In a Sea of Energy Data, Utilities Try to Inspire Conservation

BLOG:

Explosive hypothesis about humans' lack of genetic diversity
Diet Sodas May Not Be As Harmless As You Think
Health Officials to Consider Tightening Vaccine Exemptions
Scientists Understand Heart Disease Better, Still Give Bad Advice
The Megalodon's Descendants
Famous African American Scientists & Innovators: Part II
Swine Flu – A Virus or a Bacteria?
Cyber Wolves in (Fire)Sheep Clothing
Why Do Mosquitoes Buzz in People's Ears?
15 Months Later, Rediscovered San Francisco Plant Thrives