If you’re even remotely interested in science, you probably heard the figurative bombshell dropped by NASA yesterday: They have found life on Earth that can build its genetic structure from arsenic. If you want the whole story, please read one of the journalistic articles; they will answer all your questions. But many friends have been asking me what my take on arsenic-based life is, and why it’s important. As it turns out, Element 33 and I share some history.
Here are the basics. There are six essential elements to life: Carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Phosphorus’ job in the life cycle is to make the backbone of the DNA double helix, and to act as a power source or battery as the “P” in “ATP,” which is the basic unit of currency for energy in all living things. It’s a pretty important job, you’d have to say. What astrobiologists working with a strain of Halomonadaceae protobacteria found in California’s Mono Lake discovered was that, if they starved the microbes of phosphate, while force-feeding them arsenic — which sits right below phosphorus on the periodic table, and shares many of its attributes — they could coerce the microbes into using arsenic in the place of phosphorus to build their DNA and energy base.
Halomonadaceae GFAJ-1, pictured above.
Disappointing, you say? Perhaps you were hoping for the discovery of poisonous Loch Ness Monsters oozing arsenic from their skin below Mono Lake? First, consider that phosphorus was once considered essential for all life. If you had a giant blender, and were to make five milkshakes out of a tree, a salamander, a mushroom, a bunch of E. coli, and a frozen mastodon penis, respectively, you’d find the same six elements in each shake. The fact that living things can replace one essential element with another means that they also probably do, which means that life is possible in far more places than we ever imagined. There could be life on a moon of Saturn that uses silicon instead of carbon, or selenium instead of sulfur. There could be a shadow ecosystem of microbes made of arsenic living unnoticed under our feet. And if so, and life evolved twice independently on Earth, it’s more than twice as likely that life has evolved on other planets, ending the supposed exceptionalism of our lonely space rock and suggesting that that we have interstellar neighbors.
This story is not about Mono Lake or arsenic, says Felisa Wolfe-Simon, the lead researcher, in the NY Times article, but about “cracking open the door and finding that what we think are fixed constants of life are not.” But for a second, let’s consider that insidious doppelganger of phosphorus, and that toxic lake in the foothills of the Sierra Nevada which is so important to so many life forms.
I first encountered Mono Lake on a college geology expedition. I was tagging along for a botany project, trying to find a plant that accumulates arsenic. My college was built on an old apple orchard, and the lead arsenic once used as a pesticide and fungicide on the apples remained in the soil; a plant that grew around arsenic-heavy hot springs could be used for bioremediation. Arsenic, a metalloid or semi-metal, is poisonous precisely because it resembles phosphorus so much; living things take it into their cells and try to jam it into their machinery, where it usually wreaks havoc and kills the cell. It has only ever been used by humans as a poison and a weapon, though it was briefly fashionable in Victorian England for ladies to ingest trace amounts to lighten their complexion.
Just a half-teaspoon of arsenic, please.
One such font of arsenic was the alkaline Mono Lake. Because no river runs from it, leaving all water to simply evaporate, it is three times saltier than the ocean. Tufa towers, great stalagmites made where calcium-rich water once fountained up into the lake when it was larger, stand like sentries and turrets around its shore. The only creatures that can tolerate its hypersalinity, its high arsenic content, and its pH level of 10 — approaching that of pure ammonia — are the alkali flies bouncing on its sandy shore, and a species of brine shrimp found nowhere else on Earth. A single-celled algae gives the lake its bottle-green tint, and forms the base for its very short food chain. But while neither fish nor frog can live in the lake, it’s visited by 2 million migrating shorebirds each year: avocets, killdeer, grebes, and one of my personal favorites, red-necked phalaropes. The lake is crucial to these birds, as it’s the only safe haven in the desert for hundreds of miles, a toxic oasis. Here, the phalaropes can safely putt-putt around like toy motorboats in a bath, pecking sea monkeys from the surface with their needle-like beaks.
The Red-necked Phalarope also enjoys demolition derbies and flavored chaw.
Why does Mono Lake matter? Because it is almost as close as we can come on Earth to the conditions that might have existed when life was first formed. Planets are always toxic places at some point in their story; indeed, we’ve never found another that has grown out of its volatile phase. But the lifeless appearance and toxic demeanor of Mono Lake are deceiving; as Mono Lake has its extremophiles, so might some young planet full of volcanoes and saline lakes. As I’m fond of saying, wherever life can exist, life will exist, and now that we know that life can be built with more elements than previously known, the great undiscovered zoo of the universe just got potentially more crowded. There may be a planet which, like us once, has plenty of arsenic available in its deserts, but only sparse concentrations of phosphates with which to make its genetic material. In fact, our very first ancestors may have been animated in a pool very much like Mono Lake, using arsenic instead of phosphorus first, and switching later on as the element became available. The origins of all life on Earth may have been born in a lake of poison.
There is, however, such a thing as too much poison. Since the 1940′s, Los Angeles has been piping the groundwater that supplies Mono Lake to its urban base, shrinking it and turning it even more salty. Its one tiny island, which is the second-largest nesting site for California gulls, now becomes a peninsula during droughts, leaving eggs and chicks available to coyotes. Should the weather change more permanently, it’s quite possible that the haven for millions of birds, and the home of the only alternate life we’ve ever found, will dry up and disappear entirely. Even badlands need to exist, for these wild and dangerous places harbor the far-flung treasures of evolution, and perhaps even the key to life itself. We were born in the badlands. The other planets in the galaxy are the badlands. We have a duty to preserve the acidic, basic, saline, lonely, volcanic, frigid places, because they are where we come from, and what we will find in our future. Mono Lake, home of brine shrimp and arsenic-loving bacteria, is a national treasure. And as the troubadours once sang on its shores, “You don’t know what you got ’til it’s gone.”