One of the great unanswered questions of our age is whether, amongst the 70 sextillion stars, this little rock of ours is the only one with life (and intelligent life) on it. Amid the rough and tumble of wars, economic crises, and our best attempts to bugger up our only home, scientists have been puzzling away at this question for the past few decades, and despite the lack of headlines, have been making steady progress.
As noted in this LP post from 2007, planet-hunting has improved to the point where we’ve found solar systems that are somewhat like our own. The Kepler space telescope, recently launched by NASA, is the next major step in this process. It will examine many thousands of stars for planetary systems, and hopefully find a large number of “Goldilocks planets”, not too big or small, and in the right distance from their suns for liquid water to occur (considered an essential for life). However, detailed scrutiny of these planets will have to wait for the next generation of space telescopes, hopefully in the coming decades!
In the meantime, some biologists are thinking anew about another part of the Drake equation – fl.fl is our estimate of the probability of planets, where conditions are “suitable for life” (for some definition of “suitable”), actually developing life. Was life on Earth inevitable, given its location? Or was it a freak event, so rare it hasn’t occurred elsewhere in the observable universe?
Traditionally, it’s been thought that the only way to answer this question is to observe enough “suitable” planets and see how many have life on them. As noted, that’s not currently possible. But what if life emerged from non-life multiple times on Earth? If we were able to show that life got going twice or more on Earth, that would be pretty good evidence that life will emerge reasonably readily given the right conditions. However, at first glance, the odds of finding evidence for such multiple emergences sound pretty low. For a start, every living thing we’ve found thus far – from humans, to eucalyptus trees, to moss, to amoebas, and everything in between – seems to have common ancestry, somewhere back far enough. Secondly, if the precursors of life existed on Earth now, or in the last few hundred million years or so, existing living things would gobble them up long before.
But, as this New Scientist article explains, it might just be possible that a “shadow biosphere” – a second, independent family tree of life – is living right under our noses, and examines a number of ways we can look for it. These include examining extreme environments where there’s no “conventional” life, or looking for complex molecules that don’t fit the normal patterns we expect from the living things we’re familiar with.
It’s impossible to know, at this stage, whether these searches will succeed in finding a shadow biosphere. Even if one exists, or did exist at some past stage, there’s no guarantee that we’ll be able to find it. But it’s just possible that rather than finding it through a telescope or space probe, we might find alien life right under our noses in a local hot spring or desert.
I don’t have time to read the article but endosymbiosis would gobble up a great deal of a ’shadow’ biosphere as well and make it appear indistinguishable from the larger tree.
As Lipid studies get better there may be some interesting structures found that have been co-opted.
I’m no biologist, so I had to check what endosymbiosis was. According to Wikipedia’s article, it’s where an organism lives entirely within another, and the two separate organisms work together fr each other’s benefit.
The most famous example is Mitochondria, which seem to have originated as a type of bacteria, and now serve as the “power plants” within our cells.
“For a start, every living thing we’ve found thus far – from humans, to eucalyptus trees, to moss, to amoebas, and everything in between – seems to have common ancestry, somewhere back far enough.”
What about the stuff found in the Kerala red rain?
The claims that the Kerala red rain is of extraterrestrial biological origin are not, to put it mildly, widely accepted in the scientific community.
Archaea are relatively good candidates. They exist at the base level (the real base level) and might not be interrelated to other organisms.
They also tend to only exist as extremophiles. In other words the only niches they can compete in are the ones that give them an edge over bacteria – inside nuclear reactors, in 400 degree superheated water, inside glaciers and so on.
The Archaea have recognisable DNA – I think the scientists are looking for something even more exotic and perhaps not even carbon based. Anything with DNA would be a little boring for them.
I’m quite taken by the idea that earth has spawned several life forms in its life time, and some of them successfully left
David: if there was evidence that archea DNA didn’t share a common ancestor with all other life, that would be a very big discovery in its own right.
Maybe. The fact that the Archea share many DNA transcription similarities with bacteria make this unlikely, although this discounts the idea that the Archea independently evolved this method in the same way that flight has evolved independently several times.
If you can find the smoking gun that says the general thrust of organic chemistry always leads to things like polymerase and long sequences of nucleotides we might be in with a better shot at narrowing down genuinely different strands of life within carbon based forms at least. It can’t be the only way of making instructions for life. If it is, there’s some interesting philosophical questions to be answered.
“These include examining extreme environments where there’s no “conventional” life”
I thoroughly recommend this IMAX film, Volcanos of The Deep Sea, which I viewed in New York some years ago.
(sorry for the lengthy quotation!)
First discovered in 1977, oases of life that include giant, red-plumed tubeworms live on the Pacific Ocean floor near hydrothermal vents. This is deeper than where sunlight can penetrate to provide the energy needed for photosynthesis. At the base of the food chain are bacteria that nourish themselves through a process of chemosynthesis. Drawing their energy from gases dissolved in warm or hot springs, mainly hydrogen sulfide, they are able to manufacture sugars and starches from carbon dioxide and water.
These and what turned out to be hundreds of other animal species new to science were prospering in warm springs issuing from cracks in pillow-shaped lava flows. Biologists immediately wondered how these animals could make a living, apparently without depending on nutrients generated through photosynthesis. It turned out that at the base of the food chain were bacteria that nourished themselves through a process of chemosynthesis. Drawing their energy from gases dissolved in the warm springs, mainly hydrogen sulfide, they were able to manufacture sugars and starches from carbon dioxide and water.
The Galápagos discovery was soon followed by the revelation of similar ecosystems at hot springs discharging from spectacular “black smoker” vents along the ridge system in the Pacific. The temperatures in these hydrothermal vents ranged as high as a scalding 750 degrees Fahrenheit (400 degrees Celsius). With these discoveries geologists realized that the ocean basins are really leaky places. The cold, heavy seawater can sink downward for miles, through cracks in the underlying volcanic rock. There it is heated as it flows near reservoirs of magma at sites beneath the ridge system, expanding and rising until it discharges from the seafloor. Along the way it dissolves metals and picks up gases from the rocks and the magma. The metals precipitate out of solution as iron-rich sulfides, coalescing into chimney-like structures and pouring into the surrounding cold seawater as a black cloud of particles (hence the name “black smoker”).
For marine biologists, discovering these new ecosystems was like being a member of a Star Trek crew and finding a previously unknown basis for life on another planet. More astonishing still, certain heat-loving, chemosynthetic microorganisms living in those ecosystems turned out to have genetic characteristics that place them near the base of the tree of life. That raises the tantalizing possibility that life on Earth began at such hydrothermal vents in the early ocean, rather than in shallow waters at Earth’s surface.
Seeing ‘new’ 50-500 million year old Paleodictyon hex-mosaic burrows discovered, was more than inspiring.
(and I agree with Michael S.)
Actually, as the song goes, I think it’s a matter of hoping there’s intelligent life out there, because it’s questionable how much there is here.
Personally it would more astounding to think that this rather inconspicuous rock on the outer edge of a medium sized spiral galaxy could be the only place where life arose in the entire universe.
In fact, that seems unbelievable to me.
Life it seems to me must be universal.
Though until we actually find something physical out there that doesn’t fit the usual mold of life on earth, it’s certainly a point of debate and curiosity.
If we do find extraterrestrial life like us, it seems like good evidence of panspermia, the ongoing spreading of life through the universe. The earth leaves a fine trail of fungal spores, bacteria and tiny fragments of life as we pass through space on our loops around the sun. With the right equipment, from far away, I’m sure all these molecules of life would be visible streaming behind the earth. Not to mention all the water laying around on the surface and in the atmosphere.
One thing we do know about life on Earth is that it took a hell of a long time (2.5 billion years or so) to get from single celled creatures to the earliest animals, which appeared at most a billion years ago. Indeed, it may have taken a billion and half years just to get as far as multi-celled organisms. Of course we don’t know whether these times are typical, unusually slow, particularly fast, or a complete fluke anyway. Still, once singled celled life evolved, there was presumably no shortage of material on which evolution could work. That it took so long for animals to appear suggests that it’s just not a very likely process, unless the Earth was freakishly unlucky. In another billion years or so, the Earth will become uninhabitable due to the sun warming up (as stars do as they age), so intelligent life was cutting things a bit fine. On the whole, I won’t be putting any money on intelligent life being found anywhere but on Earth.
One thing we do know about life on Earth is that it took a hell of a long time (2.5 billion years or so) to get from single celled creatures to the earliest animals, which appeared at most a billion years ago. Indeed, it may have taken a billion and half years just to get as far as multi-celled organisms. Of course we don’t know whether these times are typical, unusually slow, particularly fast, or a complete fluke anyway. Still, once singled celled life evolved, there was presumably no shortage of material on which evolution could work. That it took so long for animals to appear suggests that it’s just not a very likely process, unless the Earth was freakishly unlucky. In another billion years or so, the Earth will become uninhabitable due to the sun warming up (as stars do as they age), so intelligent life was cutting things a bit fine. On the whole, I won’t be putting any money on intelligent life being found anywhere but on Earth.
Sylvia – do you mean intelligent life being found, or are you stating your belief about its likely existence. They’re pretty different.
If you are talking existentially rather than empirically, I have something for you to ponder in statistical terms.
Number of planets where we know for sure whether life exists or has ever existed = 1.
Number of planets where life could exist = infinity, give or take.
At that rate, you’d expect a fair bit more life out there, wouldn’t you?
No complex living creature exists outside a whole web of life, except perhaps the primordial cell(s)… whatever, wherever that was.
The more complex creature arise from a more complex environment/web of life.
Many creatures have abilities and senses well beyond our natural capabilities and have survived largely intact for millions of years. If humans can really be considered intelligent, I think it is through an inherent intelligence in the web of all life, of which we are a recent part/manifestation. No designer, just the warp and weft of many natural forces and players, and time.
If we actually ran across another planet at the same stage as us would we really want to know them? or let them know about us? I’m sure at least a few of us couldn’t help ourselves, for better and worse. Same perhaps for them.
What you foolish fluid-based Tellurians do not grasp with your hairy little primate paws is that your species was bred as public transport system for H20.
And now you are running out of it, we have mind-meld harnessesed you as a replication system for silicon profligation – using our Hungary moles like Zsa Zsa Andy Groves Groves Teller.
Yes, soon you realise everything is iEverything, talking, breeding and swapping mp3 derivatives with need of each of other but without any need for you fleshy bags of liquid anymore. Yes, you will be is prawned!
Then Boskone arrives – once we are receiving all clear loltextz alert.
I said – once we are receiving all clear loltextz alert!
Ahem, could feeble Tellurian stooge prod Boskone lolcat agent awake and put batteries back in sphere of communication?
If you do, a life not in the off-world colonies awaits. Plus macho tuna.
Hurry fast, our elite roomba and kreepy krawly shock troops are massing under your leisure timez.