The Oldest Stuff on Earth

The Cosmic Pathway (coolest name for an exhibit ever) at the American Museum of Natural History spirals down through thirteen billion years of universal happenings and drops its visitors off at the entrance to the Gottesman Hall of Planet Earth. The Hall of Planet Earth appeals enormously to my inner geology geek, with displays ranging from chunks of black smokers (hydrothermal vents on the ocean floor where sulfide deposits build up and where life, it is theorized, may have begun on Earth) to lava samples from around the world to parts of an ice core from Greenland that’s been crucial to our understanding of climate change. Thrilled as I am to get to see these things, I am always a little disappointed by the specimen that I think should be the coolest part of the hall: a zircon crystal, found in Australia in the 1990’s, that is one of the oldest known pieces of Earth, at 4.3 billion years.

Zircon is an impossibly resilient mineral that scientists love because it contains uranium, which is unstable and breaks down to lead over a known time period—thus, we can use radiometric dating to find out how old the zircon crystal is. In fact, the radioactive material inside zircon crystals sometimes destroys the mineral itself over millions of years by emitting radiation, so that the mineral's structure is destroyed and the crystal is discolored (picture: right). If you catch sight of one of these so-called ‘metamicts’ in the field, it looks just like a tiny radioactive bomb went off—a brownish dot surrounded by little fractures in the surrounding rock.

In the Hall of Planet Earth, however, the zircon crystal just looks like a little lump of rock, which for some reason disappoints me. I suppose it seems that a remnant of Earliest Earth should be more obviously imbued with some quality of specialness—some sort of iridescent, diamond-in-the-rough sparkle (perhaps the Hall of Planet Earth, while appealing to my inner geology geek, fails to appeal to my inner Lord of the Rings geek).

At any rate, the zircon is special because it is one of the oldest materials on Earth, having formed just a couple hundred million years after the planet itself (Earth’s estimated age is about 4.6 billion years). While the 4.3 billion year-old zircon was certainly a fun find for science, the mineral had out-survived the rest of the rock with which it formed—in other words, while the other minerals in the rock melted and/or deformed and became new rock again, the zircon mineral remained solid, eventually re-incorporating as part of a newer, younger rock.

What scientists have been searching for, then, is rock that is as old as the zircon crystals inside—rock that formed just as the Earth was settling out into layers and cooling to a temperature that allows rock to solidify (the geologic word for this earliest eon of Earth is the Hadean: Earth then was a fiery, violent mess replete with extraterrestrial bombardments and volcanic activity). Because Earth’s crust is so often created and destroyed in the generative and destructive processes of tectonics and erosion, really old rock is tough to find-- the oldest rock in New York City is about 1.3 billion years, and a good deal of the land below us is much younger.

Scientists working in northern Quebec on the Hudson Bay believe they may have found some of this very old rock—a little exposure of Earth’s proto-crust. The dated material in this rock (it’s an area composed mostly of a rock named faux-amphibole, whose chief mineral component is Cummingtonite….I remember the day in mineralogy class when a fairly humorless professor lectured on this very mineral-- suffice it to say that we geology students, ever fond of questionable-sounding jargon, had a tough time keeping our faces straight) is about 4.28 billion years old. If the rock itself is as old as some of the minerals inside, scientists have an opportunity to take a close look at some of the first crust that ever formed on Earth. In doing so, they can begin to answer questions about how crust formed back then and to compare Earth’s early geologic processes with the processes occurring today.

If the rock does turn out to be proto-crust from 4.28 billion years ago, I hope the Hall of Planet Earth gets a chunk of it-- even if it’s not much to look at.

Superstition: Was Stevie Wonder Wrong?

Having grown up in a fairly superstition-free household (exception: see my mother’s diet books), I have always experienced a good deal of discomfort when confronted with a real-life, authentic subscriber to the more overt and antiquated superstitions of our time. My first experience with superstition occurred while walking down the sidewalk with my friend Helen in the first grade. I can’t remember the exact circumstances, but I know that she suddenly shouted at me, triumphantly and mockingly, “stepped on a crack, you’ll break your mother’s back!” When pressed for an explanation linking cause and effect, Helen retreated into a self-satisfied smirk, and advised me with her arms crossed over her chest to “wait and see.”

In the end, Helen proved fond of spurning appeals to reason. Our friendship ended abruptly during the summer after first grade, on the swing-set behind her house. I had done something wrong, and followed up the misdeed with an apology. In response, she told me that “sorry doesn’t feed the bulldog.” Then she ran inside, to tell on me to her mother, who took her side.

The reason I bring up the matter of superstition now, in the first post of a blog supposedly devoted to science: a study published last week by the Royal Society, exploring the evolutionary basis for superstition and superstitious-like behavior. The study found, using a mathematical model, that it does indeed benefit an organism to adopt superstitious tendencies—to assign, incorrectly, a link between various causes and effects. The reason why? Something analogous to Pascal’s Wager—the argument for belief in God which holds that the possible benefit outweighs the possible risk (while the decision theory used in the argument is sound, the Wager itself is now understood to be based on a number of problematic assumptions). Taken into the realm of natural selection, the idea goes that the risk associated with holding a superstition (assigning false causality) is less than the risk of failing to assign causality when it does, indeed, exist.

Here in New York City, this scientific finding may help explain the wild success enjoyed by our perpetually-thriving population of rats. Rats have a number of things going for them in terms of survival—namely, a love of sex coupled with an iron-clad reproductive system, and a keen ability to avoid our attempts to kill them. Rats can taste poison in as small a dosage as .5 parts per million (think two grains of salt in a pound of peanut butter). Also—and here’s where the superstition comes in—rats pick up social cues about what to eat and what not to eat. If a rat returns to its burrow healthy and reeking of hangar steak from the restaurant down the alley, the other rats in the burrow will learn that the hangar steak is potentially safe. If, on the other hand, an unwell rat returns to the burrow smelling of, let’s say, the same restaurant’s ratatouille, the rats will be likely to consider the ratatouille a potential risk and avoid eating it. While these assignments of causality are probably wrong most of the time, they are more likely to benefit the community of rats than to harm it. Thus: superstition as an adaptive behavior.

I hate to think that Helen’s persistence in superstition could be, in any way, of evolutionary benefit. I also hate to think that the boy I (and everyone else) knew in high school who refused to wash his jock strap for the entire football season was somehow acting on a successful survival-related impulse. And yet, there’s something comforting in the idea that our own moronic conclusions can help keep us alive. Or is there?

Sources:
Article: "The evolution of superstitious and superstition-like behaviour"
Also, Jerry Langton's fun book about rats.