What life on Earth tells us about life ‘elsewhere’

Plumes of water seen erupting form the surface of Saturn's moon Enceladus. NASA/JPL-Caltech and Space Science Institute
Plumes of water seen erupting form the surface of Saturn’s moon Enceladus. NASA/JPL-Caltech and Space Science Institute

In 1950, the physicist Enrico Fermi asked a question not many could forget for a long time: “Where is everybody?” He was referring to the notion that, given the age and size of the universe, advanced civilizations ought to have arisen in many parts of it. But if they had, then where are their space probes and radio signals? In the 60 years since, we haven’t come any closer to answering Fermi, although many interesting explanations have cropped up. In this time, the the search for “Where” has encouraged with it a search for “What” as well.

What is life?

Humankind’s search for extra-terrestrial life is centered on the assumption – rather hope – that life can exist in a variety of conditions, and displays a justified humility in acknowledging we really have no idea what those conditions could be or where. Based on what we’ve found on Earth, water seems pretty important. As @UrbanAstroNYC tweeted,

And apart from water, pretty much everything else can vary. Temperatures could drop below the freezing point or cross to beyond the boiling point of water, the environment can be doused in ionizing radiation, the amount of light could dip to quasi-absolute darkness levels, acids and bases can run amok, and the concentration of gases may vary. We have reason to afford such existential glibness: consider this Wikipedia list of extremophiles, the living things that have adapted to extreme environments.

Nonetheless, we can’t help but wonder if the qualities of life on Earth can tell us something about what life anywhere else needs to take root- even if that means extrapolating based on the assumption that we’re looking for something carbon-based, and dependent on liquid water, some light, and oxygen and nitrogen in the atmosphere. Interestingly, even such a leashed approach can throw open a variety of possibilities.

“If liquid water and biologically available nitrogen are present, then phosphorus, potassium, sodium, sulfur and calcium might come next on a requirements list, as these are the next most abundant elements in bacteria,” writes Christopher McKay of the NASA Ames Research Center, California, in his new paper ‘Requirements and limits for life in the context of exoplanets’. It was published in Proceedings of the National Academy of Sciences on June 9.

Stuff of stars

McKay, an astro-geophysicist, takes a stepped approach to understanding the conditions life needs to exist. He bases his argument on one inescapable fact: that we know little to nothing about how life originated, but a lot about how, once it exists, it can or can’t thrive on Earth. Starting from that, the first step he devotes to understanding the requirements for life. In the second step, he analyzes the various extreme conditions life can then adapt to. Finally, he extrapolates his findings to arrive at some guidelines.

It’s undeniable that these guidelines will be insular or play a limited role in our search for extraterrestrial life. But such criticism can be partly ablated if you consider Carl Sagan’s famous words from his 1980 book Cosmos: “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.”

In 1991, RH Koch and RE Davies published a paper (titled ‘All the observed universe has contributed to life’) presenting evidence that “a standard 70 kg human  is always making about 7 3He, 600 40Ca, and 3,000 14N nuclei every second by radioactive decay of 3H, 40K, and 14C, respectively”. In other words, we’re not just made of starstuff, we’re also releasing starstuff! So it’s entirely plausible other forms of life out there – if they exist – could boast some if not many similarities to life on Earth.

To this end, McKay postulates a ‘checklist for habitability’on an exoplanet based on what we’ve found back home.

  • Temperature and state of water – Between -15° C and 122° C (at pressure greater than 0.01 atm)
  • Water availability – Few days per year of rain, fog or snow, or relative humidity more than 80%
  • Light and chemical energy sources
  • Ionizing radiation – As much as the bacterium Deinococcus radiodurans can withstand (this microbe is the world’s toughest extremophile according to the Guinness Book of World Records)
  • Nitrogen – Enough for fixation
  • Oxygen (as the molecule O2) – Over 0.01 atm needed to support complex life

McKay calls this list “a reasonable starting point in the search for life”. Its items show that together they make possible environmental conditions that sustain some forms of chemical bonding – and such a conclusion could inform our search for ‘exo-life’. Because we’re pretty clueless about the origins of life, it doesn’t mean we’ve to look for just these items on exoplanets but the sort of environment that these items’ counterparts could make possible. For example, despite the abundance of life-friendly ecosystems on Earth today, one way life could have originated in the first place is by meteorites having seeded the crust with the first microbes. And once seeded, the items on the checklist could have taken care of the rest.

Are you sure water is life?

Such otherworldly influences present yet more possibilities; all you need is another interstellar smuggler of life to crash into a conducive laboratory. Consider the saturnine moon Titan. While hydrocarbons – the principal constituents of terran life – on Earth are thought to have gassed up and out from the mantle since its formative years, Titan already boasts entire lakes of methane (CH4), a simple hydrocarbon. A 2004 paper by Steven Benner et al discusses the implications of this in detail, arguing that liquid methane could actually be a better medium than water for certain simple chemical reactions that are the precursors of life to occur in.

Another Solar System candidate that shows signs of habitability is Titan’s peer Enceladus. In April this year, teams of scientists studying data from the Cassini space probe said there was evidence that Enceladus hosts a giant reservoir of liquid water 10 km deep under an extensive ice shell some 30-40 km thick. Moreover, Cassini flybys since 2005 had shown that the moon had an atmosphere of 91% water vapor, 3-4% each of nitrogen and carbon dioxide, and the rest of methane.

These examples in our Solar System reveal how the conditions necessary for life are possible not just in the Goldilocks zone because life can occur in a variety of environments as long some simpler conditions are met. The abstract of the paper by Benner et al sums this up nicely:

A review of organic chemistry suggests that life, a chemical system capable of Darwinian evolution, may exist in a wide range of environments. These include non-aqueous solvent systems at low temperatures, or even supercritical dihydrogen– helium mixtures. The only absolute requirements may be a thermodynamic disequilibrium and temperatures consistent with chemical bonding.

As humans, we enjoy the benefits of some or many of these conditions – although we know what we do only on the basis of what we’ve observed in nature, not because some theory or formula tells us what’s possible or not. Such is the amount of diversity of life on Earth, and that should tell us something about how far from clued-in we are to understanding what other forms of life could be out there. In the meantime, as the search for extra-terrestrial life and intelligence goes on, let’s not fixate on the pessimism of Fermi’s words and instead remember the hope in Sagan’s (and keep an eye on McKay’s checklist).

Life notes

The marching coloumns

Every day is a swing between highs and lows, and in the last two months that I’ve experienced them, they’ve never been periodic. Setting off the work, the mood depends on the weather: cloudy is good, buoyant, rain is more than welcome, but a clear, blue sky and a blazing fireball in the empyrean is a dampener on my spirits, if not on anyone else’s. How will I work if I’m sweating all the time? Hmm.

The traffic in my erstwhile small city has grown to draconean proportions. Some argue that it’s a good sign, a sign of the city turning into a metropolis. I don’t like it. It not only places more minutes, more hours between work and home, home and work, between the factories and the beach, between the railway stations and the travel-shops, but it turns nice auto-drivers into pissed-off tyrants whom you simply don’t want to run into.

It takes nothing to precipitate all this but the clock striking 6. Areas and wards transform from familiar crenelations of microscopic economies, communities of traders, sweatshop toilers, and flower-braiders to hotbeds of rage, of exodus and maddened intra-urban migration… Suddenly, friends want to leave, fathers want to be left alone, mothers want to vent, and sisters want only to know what the hell’s going on.

If you’re in Chennai and traveling by auto in the evenings, I suggest you carry a book, or a Kindle, or a smartphone with which to kill time. It’s a time-warp, absolute and unrelenting chronostasis, with a profanity-drenched metronome ticking away like a time-bomb in the seat in front of yours. Of course, there are also people pushing, people shoving their way through the maze of vehicles. For every mile, I suppose it’s 10 points, and for every deceptively shallow pothole surmounted, 50.

In this crazy, demented rush, the only place anyone wants to be is on the other side of the road, the Place Where There Is Space, a vacuum on the far side that sucks the journeymen and journeywomen of Chennai into a few seconds of a non-Chennai space. When I ride in an auto on such days, I just don’t mind waiting, for everyone to pass by. I don’t want to make enemies of my fellows. At the same time, I never might know them better than their mumbled gratitude when I wave them ahead.

The driver gets pissed off, though. Starts to charge more, calls me “soft”, and that I don’t have what it takes to live and survive in the city. I tell him I can live and survive in the city alright, it’s just the city that’s not the city anymore. Sometimes, the driver laughs; most times, it’s a frown. In that instant, I’m computed to become an intellectual, and auto-drivers seem to think intellectuals have buttloads of money.

The only thing these days that intellectuals have buttloads of is tolerance.

Tolerance to let the world pass by without doing anything about it, tolerance to letting passersby jeer at you and making you feel guilty, tolerance to the rivers that must flow and the coloumns that must march, tolerance to peers and idols who insist something must be done, tolerance to their mundane introspection and insistence that there’s more to doing things than just hoping that that’s a purpose in itself.

It’s circular logic, unbreakable without a sudden and overwhelming injection of a dose of chaos. When the ants scurry, the mosquitoes take off, and the elephants stampede, all to wade through an influx of uncertainty and incomprehension and unadulterated freedom, real purpose will be forged. When children grow up, they are introduced to this cycle, cajoled into adopting it. Eventually, the children are killed to make way for adults.

With penises and vaginas, the adults must rule this world. But why must they rule? They don’t know. Why must they serve? They don’t know. Yeah, sitting in an auto moving at 1 mile an hour, these questions weigh you down like lodestones, like anchors tugging at the seafloor, fastening your wayward and seemingly productive mind to an epiphany. You must surely have watched Nolan’s Inception: doesn’t the paradox of pitch circularity come to mind?

The grass is always greener on the other side, the staircase forever leads to heaven, the triangle is an infinite mobius spiral, each twist a jump into the few-seconds-from-now future. Somewhere, however, there is a rupture. Somewhere inside my city, there is a road at the other end of which there is my city in chronostasis, stuck in a few-hours-from-now past.

Where auto-drivers aren’t pissed off because the clock struck 6, where fathers and mothers realize nothing’s slowed down but just that their clocks have been on fast-forward of late, where snaking ribbons of smoke don’t compete for space but simply let it go, no longer covet it, only join in the collective sorrow of our city’s adolescence.