Recently, I saw the film “The Green Lantern” in theaters. For those of you who don’t know, the Green Lantern is a DC Comics franchise. The story revolves around a large intergalactic peacekeeping force known as the Green Lantern Corps. The Green Lanterns come from all over the universe and are made up of thousands of different alien races. All of them, though, wear the green power ring of willpower which they can use to materialize anything they can imagine, from brick walls to hamburgers. The plot of the film involves one of these Green Lanterns, Abin Sur, who crash-lands on earth and gives his ring to a human named Hal Jordan, who spends the next couple of days being made fun of for being a human and then saving the entire universe. Also, he’s played by Ryan Reynolds.
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| Yummy. |
There is a scene in the film in which Dr. Hector Hammond (in the long-standing tradition of comic book character name alliteration) has the opportunity to examine the dead body of the alien who crash landed earlier on. Hammond (played by Peter Sarsgaard) remarks at the end as to how remarkable it is that the alien would be humanoid, which he attributes either to convergent evolution or a common ancestor. Later on his head swells up, he develops psychic powers, and he threatens the life of Blake Lively, but his point remains very interesting.
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| Oh, Blake. Who'd ever want to hurt you? |
The possibility of extraterrestrial life has captivated mankind for centuries. With billions of trillions of planets in the universe, the probability that life exists solely on Earth is impossibly small. Chances are, life exists elsewhere in the universe; probably a lot of elsewheres. Life from planet to planet could be billions of years apart in their own evolutionary paths (assuming that anywhere that life exists in competition would also foster evolution) and could on some planets be as primitive as bacteria or so advanced that we seem like bacteria to them. More important, though, than how advanced extraterrestrial life is, is what it is made of, and what it might look like.
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| My guess. |
Before we look into alien life, however, let’s take a look at how we came to be the way we are. The history of life on Earth is probably about as old as the Earth itself (4.5 Billion Years old, next month). The first fossilized bacteria are about 3 Billion years old, and there’s geochemical evidence to support the presence of life as far back as 3.8 Billion years ago. Before then, there’s a really big grey area where a bunch of rocks and water suddenly produced the first organism, the Last Universal Ancestor (LUA, to his friends). How this happened is up for debate, with the most predominant theories all having really cool names. The first major theory is the RNA World theory, which sadly does not refer to a molecular biology-themed amusement park but rather to a “pre-life” world in which RNA ruled supreme. The notion is that water, ultraviolent light, and the various compounds making up earth’s crust were enough to produce a few ancestral strands of RNA, which has the ability not only to contain genetic information and replicate, but also to act as a ribozyme, a protein-like molecule which can metabolize other compounds. These are both roles which RNA fulfills today in one form or another (mRNA molecules contain genetic information which is decoded by ribosomes which are essentially giant ribozymes which make all the proteins necessary for life). With enough active RNA, larger and larger ribozymes could be formed and DNA, the much more stable genetic molecule could evolve to take over and eventually give way to cellular life. Some scientists believe that this process was only possible under primordial conditions while others believe that it continues today. Of course, any pre-RNA which would arise today would be eaten by something almost immediately, which makes it a tricky theory to test.
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| Mmm Mmm Good. |
The second major theory is that life did not originate here at all, and that the planet was early-on contaminated by microorganisms, either by alien visitors (who I suppose sneezed or something) or by a meteor. There is some evidence to support this, as nucleotides (the parts of DNA that store the genetic information) have been found inside meteorites. Now, you might be asking yourself where these microorganisms might have originated from. Well, the scientific community reckons that it had to originate someplace and that it probably did so by something close to the RNA World theory. Return to Dr. Hammond and the purple alien who gave Van Wilder the magic ring. If in fact DNA came to this planet from someplace else, then life that evolved on that planet would have a very similar starting point to us. DNA survives best under some very precise conditions (temperature, pH, biochemical environment, etc.) and if extraterrestrial DNA-based life was going to survive, it would have to do so in an environment which is at least somewhat similar to ours. Given the same primordial matter under similar conditions, it is entirely possible that alien life would evolve along similar a similar path as life here did. Would this result in a purple humanoid? Perhaps, though factors such as ocean coverage, temperature, amount of sunlight, and gravity might make them look a little bit less like Temuera Morrison in a costume.
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| Just a simple alien trying to make his way in the universe. |
Another point that Dr. Hammond brings up is the possibility of convergent evolution. Convergent evolution is the process by which organisms take two separate paths but end up at the same place. Take the mangrove for example. The mangrove is a type of tree which is able to grow in salt water (which most plants dislike). While there are several different species of mangrove tree, many of them are only very distantly related. This is because different kinds of trees eventually evolved a similar system of salt tolerance, which results in unrelated mangroves looked very, very similar. The notion brought up in The Green Lantern stipulates that, in a situation in which life on two different plants evolved completely separate from one another, evolution would end up producing very similar end-products (in this case, sentient humanoids with thumbs). The idea behind this is that something about a particular physiology (in this case, sentient humanoids with thumbs) is so effective at survival that it would naturally predominate in any competitive environment, in much the same way that the sphere (being the shape with the highest volume-to-surface area ratio) is the preferred shape of planets, suns, and bubbles. It just works. This theory holds up particularly well if DNA would originate as the genetic information molecule on other planets as well.
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| Note: not all organisms with thumbs are necessarily sentient. |
The chances of DNA, an incredibly complex molecule, originating on two separate planets are actually pretty slim. It’s possible that life only works with DNA (we certainly have never found a living thing that didn’t have or depend on DNA for survival), and that only planets which evolve DNA are capable of supporting life. It is also possible, however, that any number of other molecules could serve as carriers of genetic information. For example, our DNA is carbon-based. Carbon is electronically similar to Silicon, which forms similar structures with oxygen, nitrogen, hydrogen, etc. On, say, a highly volcanic planet with an average temperature of 1000 °C, a silicon-based molecule might fare much better than DNA, and give rise to a variety of silicon-based life forms. Even if we stick with carbon, there are many ways of diverging from our own DNA. Earth DNA consists of four nucelotides, but there’s no reason why alien DNA couldn’t use six or eight or even use a completely different four. It’s also completely possible that any number of other completely foreign molecules could serve a similar purpose as our own DNA. The implications of this are mind-boggling. Evolution could occur by completely different mechanisms. Cells could potentially evolve quickly within organisms rather than slowly from generation to generation. Any number of scenarios are possible.
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| On Candyplanet, the DNA is made from candy. |
Return to Ryan Reynolds at the alien crash site. Let’s say that whatever landed there, while friendly, is based on a completely different genetic system. And let’s say that the molecules as a result of that system are highly toxic to DNA-based life (DNA is kind of fragile, and the only reason why it isn’t destroyed by proteins is because evolution does not favor such a suicidal system). When Ryan gets to close and Abin Sur breathes on him it could result in a quick, horrifying, and generally painful genetic breakdown of Ryan Reynolds’ entire self. And who’s to say that whatever microbes kill him don’t consume his organic matter, multiply, and kill off the rest of the planet, too? Granted, this sounds extreme, but an organism’s molecular genetics is responsible for every protein and chemical in the body. Everything on Earth uses DNA and so we all have similar biochemistry. Mix that with a completely different system, and there’s bound to be some sort of adverse reaction. Suffice it to say, if we ever do encounter alien life, it’s as likely to kill us by breathing on us as it is by shooting us with ray guns. If this makes you sad or scared about the future of our species in the vast and lonely universe, here’s a photo of Ryan Reynolds to cheer you up.
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| Still Yummy. |
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