Psychedelic Apes Page 16

  What if alien life exists on Earth?

  You’re very similar to a slime mould. You also have many of the characteristics of a slug, an earthworm, an intestinal parasite and pond algae. But don’t take this personally. It’s not your appearance; it’s your cellular biochemistry, and you share this in common with all known life on Earth.

  Evolution has fashioned life into a bewildering diversity of forms, ranging from infectious bacteria all the way up to oak trees and elephants, but these forms are somewhat superficial. Deep down, on the cellular level, all species are more alike than different. The cells of all living things ‘speak’ the same language, which is the genetic code hidden in DNA, and they all store energy in the same way, using ATP molecules. This uniformity suggests that all life on Earth must have come from the same source material – that life must have started just once, and the many varieties of species now populating the globe all trace back to that single origin event.

  This is the consensus view of modern science, but in the early twenty-first century a small group of scientists led by physicist Paul Davies and philosopher/astrobiologist Carol Cleland challenged this orthodoxy. They didn’t dispute that all known organisms are part of the same tree of life, but they made the case that there might be unknown organisms lurking around that may belong to separate, alternative trees of life. In other words, life may have started more than once on Earth, and the descendants of those other origins might still be among us.

  The ‘biosphere’ denotes the global ecosystem of all living beings, and, in the words of Cleland, the members of those other trees of life would constitute a ‘shadow biosphere’ sharing our planet. Proponents of the hypothesis often refer to these beings, by extension, as ‘shadow life’, although sometimes they use other terms such as ‘novel’, ‘non-standard’, ‘strange’, or ‘alien life’ (alien because, while these alternative life forms may be native to the Earth, they would be profoundly foreign, from our point of view).

  These names may make it sound as if the shadow biosphere is somehow paranormal – a phantom zone bordering our own reality. That’s not the intention. Shadow life, if it exists, would be entirely physical and real. It would simply possess a biochemistry fundamentally different from our own. What it would look like, however, is unclear. Externally, it might appear to be just like standard, known forms of life, even while its inner workings would be utterly strange. Or perhaps it would be completely unlike anything biologists have seen before. We might struggle to even recognize it as being alive.

  Most scientists aren’t opposed, in principle, to the suggestion that life on Earth may have started more than once. After all, if life began by means of some natural process, which it presumably did, then this process could certainly have happened multiple times, perhaps in different geographical locations. That’s a reasonable assumption.

  But, despite this willingness to entertain the general notion of multiple origins, the scientific majority hasn’t embraced the shadow-biosphere hypothesis for the simple reason that alternative forms of life have never been encountered. It’s not as if biologists have been sitting around for the past 200 years, twiddling their thumbs. They’ve been actively peering into every nook and cranny of the natural world. If a second tree of life exists, you would think someone might have stumbled upon it by now.

  It’s a bit like the scientific objection to Bigfoot. Believers in this big hairy creature insist that a giant primate may have survived from ancient times to the present in the forests of the US Pacific Northwest. Zoologists concede that, in theory, this wouldn’t be impossible, but they point out that no biological specimens of such a creature (no hair, bones or body) have ever been found. So, as the decades pass with no sign of Bigfoot, the continuing absence of evidence eventually leads to the conclusion that he doesn’t exist. And so it is with the shadow biosphere. It would be nice to believe it exists, but the simple fact is that no one has ever produced solid evidence that anything like it is out there.

  However, shadow-life advocates counter that this analogy is flawed. Why? Because, if alternative forms of life exist, they’re probably microbial in size. The overwhelming majority of species on Earth are. In which case, they would have the entire vast microbial realm in which to hide. Current estimates suggest that as many as a trillion species of microbes might exist on the planet. Of these, only around 0.001 per cent have ever been studied by scientists. So, it wouldn’t stretch credulity at all to imagine that some of the hundreds of millions of undiscovered microbial species might be exotic types of shadow life. Tracking down Bigfoot in a forest, by contrast, would be a piece of cake.

  Finding these creatures would be particularly difficult if, on the outside, they resembled known microbes. We would never realize, by visual inspection, how peculiar they were. This is likely to be the case, since microorganisms often have fairly generic shapes. Archaea and bacteria, for example, are two distinct types of single-celled microbes that occupy entirely different domains on the tree of life. In their own way, they’re more different from each other than you are from a mushroom. But, through a microscope, they look the same. Scientists have to examine them on a genetic level to tell them apart.

  This raises the issue of the crudeness of the tools microbiologists have at their disposal, which increases the difficulty of finding any type of shadow life. Microscopes, as noted, may not help much in the search. Researchers can also try to culture or grow microbes in the lab to study them more closely, but doing so is a delicate, tricky process. It’s estimated that fewer than one per cent of known microbes have ever been successfully cultured. Shadow-life microorganisms would probably be among the 99 per cent that have never been successfully cultured. There are also various tools to analyse microbial genetic material, but these tools are designed to work with normal DNA. They would be useless for finding organisms that lacked this.

  Given the constraints of these tools, argue the shadow-biosphere advocates, it’s easy to imagine that, if there was an unusual microscopic form of life floating around out there that looked vaguely similar to known microbes, but resisted being cultured, and didn’t have standard DNA (if it had DNA at all), then it could have entirely escaped our attention.

  Biologists, if pressed, might concede this could be the case. But there’s another reason they doubt the existence of the shadow biosphere. Given the aggressiveness with which standard life has pushed into every corner of the globe, it seems likely that any rival form of life would simply have been wiped out. In other words, life may in fact have started on Earth more than once, but, due to the fierce competition for resources, presumably only the one variety of it now remains.

  But, again, shadow-biosphere advocates come right back with a counterargument. They point out that there are ways in which an alternative life form could have survived to the present day. It could have found an out-of-the-way niche to exploit, where it wouldn’t have competed directly with standard life, perhaps an extreme environment such as deep inside a hot volcanic vent or underground in a region of high radioactivity. Or perhaps it learned to feed on chemical resources that were unpalatable to standard life. If so, these odd life forms would simply have been left alone and allowed to establish an independent ecological system, side by side with us. Whatever the answer, it’s possible to imagine ways in which shadow life could have survived. It could be out there.

  Truth be told, most scientists are fairly open to these arguments in favour of the shadow biosphere – as long as they’re offered up as purely speculative ideas. However, some advocates have taken the argument one step further, and this is where the hypothesis really boils up into controversy and meets stronger resistance, crossing over into territory that mainstream science considers outrageous. These advocates not only suggest that alternative life might exist, they say they may have identified a few examples of it. They’ve compiled a list of odd stuff that, they think, may be alien forms of life here on Earth. It’s like a speculative menagerie of weird non-standard organisms. If ev
en one of the things really is non-standard life, it would be one of the most momentous discoveries of modern science.

  So, what’s on the list? One of the items is something you might have seen with your own eyes if you’ve ever gone for a hike or drive through a desert. It’s a dark, shiny substance called desert varnish that forms on rocks in arid regions. Hundreds of years ago, Native American tribes used to make petroglyphs by carving images in it, and when Charles Darwin stopped off in South America while sailing around the world on the HMS Beagle, he noticed the stuff glittering on rocks and puzzled over it.

  Desert varnish can’t have been produced by the rocks on which it forms, because it contains elements such as manganese and iron, which aren’t in the rocks. It consists of many very thin layers, which suggests to geologists that it’s been laid down by microbes. The problem is that, to date, despite a lot of investigation, no one has been able to identify a microbe that might actually be depositing it. Nor has anyone been able to figure out a non-biological way it could have formed. So, it remains a mystery. Cleland has argued that it could be an example of shadow life existing right out in the open, before our eyes.

  Nanobacteria are another, far less visible, item on the list. You need an electron microscope to see these. They’re tiny spherical particles that look somewhat like bacteria. Hence the name. But they’re much smaller – almost ten times more compact than a typical bacterium. They’ve been found in a variety of places, including rocks, oil wells and (somewhat disturbingly) human tissue.

  No one disputes that these nanobacteria exist. The controversy is over whether they’re alive. According to conventional biology, they’re far too small to be living, because all the necessary machinery of a cell (the genetic material, as well as parts to manufacture proteins and store energy) wouldn’t fit inside them. Nevertheless, some researchers claim to have seen them reproduce, and to have found DNA inside them. In 1998, the Finnish biochemist Olavi Kajander sparked an uproar when he suggested not only that they might be alive, but that they might be responsible for various medical conditions, such as kidney stones, hardening of the arteries, arthritis, Alzheimer’s and cancer. The fact that nanobacteria occupy this ambiguous status between living and non-living matter makes them, for shadow-biosphere advocates, a perfect candidate for non-standard life.

  A third exhibit in the shadow-biosphere zoo is arsenic life. These strange creatures are microbes that, purportedly, are partially made out of the highly toxic element arsenic.

  The biochemistry of all known life depends heavily on phosphorus. It’s an essential part of both the DNA and ATP molecules. But, in its atomic structure, phosphorus is very similar to arsenic, which is why the latter is so deadly. It’s hard for our bodies to distinguish between the two elements, and, when arsenic replaces the phosphorus in our cells, we die. Because the two elements are so similar, it occurred to researcher Felisa Wolfe-Simon that there might be organisms out there whose biochemistry is built around arsenic rather than phosphorus.

  She went out looking for them, and, in 2010, she claimed to have found them living in California’s arsenic-rich Mono Lake. When her findings were published online in the journal Science, they sent shockwaves through the scientific community, because these organisms, if real, would have contradicted what was believed to be a basic rule of life – that DNA is built out of phosphorus. Their existence also would have potentially proven the shadow-biosphere hypothesis correct.

  The current consensus, however, is that neither desert varnish, nanobacteria nor arsenic microbes are valid examples of shadow life. Researchers are hopeful they’ll find a non-biological explanation for desert varnish; nanobacteria are speculated to be some kind of cell fragments; while attempts to replicate Wolfe-Simon’s results at Mono Lake were unsuccessful, leading to the conclusion that they must have been caused by inadvertent arsenic contamination in her experiment. Therefore, the orthodox position remains that there’s just the one tree of life on Earth. We don’t share our planet with a shadow biosphere.

  Shadow-life advocates aren’t giving up the search, though. They explain that part of what motivates them is their desire to answer a far larger question: does extraterrestrial life exist?

  The fun way to find out would be to seek out and explore other worlds, Star Trek style. Sadly, that’s beyond our current capabilities. Passively listening for signals from alien intelligences also hasn’t turned up any evidence, and it restricts the search to technologically advanced civilizations. So, in the meantime, these advocates argue, it makes sense to look for clues on our own planet. We should try to better understand how life arose here. Did it emerge multiple times? If so, that would suggest it’s prolific – that it’s an inevitable by-product of geochemical processes and will form readily if given the chance. Confirming this would imply it probably exists elsewhere.

  But, if life arose only once here – and, as long as we don’t find any other trees of life, this is what we have to assume – that has somewhat grimmer implications. It means we can’t rule out the possibility that it may be a highly unusual occurrence. Its presence may be a magnificent one-off event. A grand cosmic fluke. So, when we look up at the sky at night, there may be nothing else out there looking back at us. We might be entirely alone in the universe.

  Weird became (partially) true: the Gaia hypothesis

  When you exercise outside on a hot day, you sweat, and when you stand around in the freezing cold, you shiver. These reactions are your body’s ways of maintaining a consistent internal temperature. No matter what conditions might be like outside, your body strives for an even 37 degrees Celsius within. Elaborate biological mechanisms have evolved to help it achieve this.

  The Gaia hypothesis, introduced by James Lovelock in 1972, makes the case that, during the past 3.7 billion years, life has been actively regulating the environment of the Earth in a similar way, using various planet-wide feedback mechanisms to maintain conditions favourable for itself. In other words, the hypothesis imagines that life isn’t a passive passenger on this planet. Rather, it’s constantly shaping and altering the Earth for its own benefit.

  To say that this hypothesis is controversial is an understatement. People either love it or hate it. For quite a while, its detractors within the scientific community prevailed, but, since the mid-1980s, aspects of the hypothesis have made a comeback and are now well accepted. Although, its supporters achieved this respectability in a curious way. They borrowed a tactic from the world of business: if your company name suffers from controversy, simply change the name. Likewise, Gaia, in its respectable form, doesn’t go by that name. Instead, it’s known as Earth system science.

  Before he dreamed up Gaia, Lovelock had already established a reputation as a brilliant inventor of chemical devices. His most famous invention was the electron capture detector, which could sniff out minute amounts of chemicals in a gas. It was this device that revealed the dramatic build-up of ozone-destroying chlorofluorocarbons in the atmosphere, leading to a worldwide ban on their use.

  Lovelock had a pronounced independent streak, which his success as an inventor allowed him to indulge by giving him the financial means to abandon both industry and academia and work for himself, out of a lab in his garden shed, in Wiltshire. He was fond of saying that most scientists nowadays are no more than slaves to their employers.

  The Gaia hypothesis started taking shape in his mind in the mid-1960s, when NASA solicited his advice on how to figure out if life existed on Mars. The space agency had assumed, based on his reputation as an inventor, that he would design a life-detecting gadget they could send to Mars, but instead it occurred to him that NASA didn’t need to send anything to the red planet. They could determine if Mars hosted life simply by analysing its atmosphere from here on Earth, because – and this was his great insight – life would inevitably reveal its presence by altering the chemical make-up of the atmosphere, keeping it in a state of disequilibrium.

  This state, he observed, was what made Earth’s atm
osphere so obviously different from every other planet in the solar system. Our atmosphere is a mix of approximately 20 per cent oxygen and 80 per cent nitrogen. Oxygen, however, is a highly volatile element. Left to its own devices, it will soon react with other chemicals and disappear. But, instead, its levels stay constant on Earth because living organisms, such as plants, keep pumping out more of it. By contrast, the Martian atmosphere consists mostly of carbon dioxide, which is chemically non-reactive. It will remain exactly the same for millions or billions of years, in a state of calm equilibrium. This suggests there’s no life there. (Although, in 2003, scientists detected occasional whiffs of methane in its atmosphere, which, being highly volatile, does teasingly hint at the possibility of life there.)

  NASA didn’t much appreciate Lovelock’s observation because it undermined the whole rationale for sending a spacecraft to Mars. Nevertheless, it got him thinking about the relationship between life and the environment, and he soon took his insight one step further. He concluded that life wasn’t just randomly modifying the environment; it seemed to be doing so in specific ways to maintain conditions favourable for itself. He noted, for instance, that over the past four billion years, the sun has grown significantly hotter as the amount of helium in it has increased. It’s part of the natural process of stellar evolution (and the bad news is that it’s still getting hotter, which in a few billion years will make the Earth uninhabitable). This should have caused the surface temperature of the Earth to rise correspondingly. But it hasn’t. To the contrary, the Earth’s temperature had remained relatively stable – at least, stable enough to maintain life. It never became a scorching inferno, like our neighbour Venus. Why?