# Evolution of Life

Since life evolved here on Earth does that mean that life had to have existed before or in the future elsewhere in the Universe or could it be a one time only freak accident ?

• – Wayfaring Stranger Oct 14 '14 at 0:08
• It could be a freak accident, but with the sheer scale of the universe, this is looking less likely. – Rory Alsop Oct 14 '14 at 9:55

Lets say you put a billion balloons on a dart board. Now lets say you throw a million darts at that dart board. If you were to pick a specific balloon and calculate the odds that THIS particular balloon would be hit by a dart, the odds would be astronomically low. However, if you were to say that at least SOME of the balloons would be popped, the odds are astronomically high.

This is why I get frustrated at those who claim that the number of coincidences that had to happen (and there are many) are too many. No, we were just one of the lucky planets out of the billions that got hit by a dart.

A "one time only freak accident" is only going to be considered as a likely possibility when scientists gain a deep understanding how life actually arises and on the basis of that can rule out that life will typically arise on Earth like planets in habitable zones. We haven't arrived at that point yet. Scientists will not invoke "freak accidents" to explain something unless there is a lot of evidence that points to that; clearly such assumptions amount to making the assumption that there is no natural explanation, but that has to be justified by other evidence first.

It almost surely did, is, and will exist elsewere in the Universe. Despite being an improbable event for a single planet, there are something like $10^{18}$ planets in the observable universe. We already have found traces of proteins typical of life on Mars and comets coming from outer space. Probably Venus could host life a few billion years ago, when it was much warmer than today.

You can see more here, about the probability of the existence of other (intelligent) creatures in our Galaxy (notice that we're not even talking about the whole Universe!):

• Expand a little on the Drake Equation and you've got a good answer here! – HDE 226868 Oct 14 '14 at 0:50

Lacking both observation of ET life and a good understanding of how life originated, this question remains a great mystery. One can never completely disprove the existence of extraterrestrial life.

There are two basic approaches to potentially answer this: one theoretical and one empirical.

• If a good theoretical understanding of the origin of life, abiogenesis, is achieved in laboratories, then the frequency of it happening given different observed exoplanetary conditions could be estimated.

• Empirically, of course we might be lucky enough to discover some statistics of actually observed living exoplanets.

But there's a third way too, the SETI way. The evolutionary steps to intelligence, to technology, to space travel all seem to benefit the proliferation of life and thus would tend to become more common over time, if they at all occur. Considering the small size of the Milky Way compared to its age and reasonable space traveling and settling speeds, one could put upper limits on how common life is.

If anyone anytime anywhere in the Milky Way developed space travel to its nearest stars, they (their offspring) should be everywhere today! They won't need to travel further than a few light years to "seed" the entire galaxy, because their Sun does the traveling through the galaxy for them. Our Sun makes a revolution every 0.25 billion years, 18 full revolutions since it was formed. We know that dinosaurs lived on the other side of the galactic center. Traveling to the nearest stars over time spreads a space traveling civilization to all over the place. If we don't find any signs of artificiality during the next few decades, given the rapid advancements in telescopy, we can say that space traveling civilizations never happened anywhere (or got too exotic for us to discover even if under our nose). And that might be extrapolated to how frequent biological evolution is overall. And most importantly, what unique event happened here to make us walk on the Moon.

On Earth, life has settled every habitable spot on Earth (everywhere where liquid water is found, life is also found). Maybe life tends to settle on interstellar scales too?

• Yes, this is the Fermi paradox isn't it ? They should be everywhere by now and yet we see no evidence of extra terrestrial life " where are they " ? SETI's reply is that they haven't been searching long enough and need a few dozen more years but why haven't they made any contact with us over billions of years ? – Peter U Oct 16 '14 at 0:02
• @Peter U Do you "contact" trees? Since they must be there, and we don't see them, they must be weirder than we can understand. – LocalFluff Oct 16 '14 at 0:20
• " Since they must be there " this has not been established yet with any proof. Different Worlds could be at different stages in development and yet we see no sign of any of them ??? The most obvious answer is that there is no one out there but I am still keeping an open mind and think that we should never give up in the search because nothing has been proven yet one way or other. Also I wanted to add that there are people that do actually try and contact trees but that is another story so we won't go into that, lol – Peter U Oct 16 '14 at 0:32
• What is most reasonable: 1) No one anywhere has ever done what we are doing here and now (how can we know what everyone everywhere has always done?) Then why haven't we discovered what makes us unique? That divine thing is per definition here were we are, still we don't see it, why? Doesn't our unique divinity exist? 2) There was once somewhere space traveling life, and therefor it is eternal and everywhere because the galaxy is so small and old and no event can exterminate interstellar life. We see it already, but we just don't know what to look for so we do not recognize it. – LocalFluff Oct 16 '14 at 0:49

Could it be a one time only freak accident?

It's rather dubious, but there's no way to rule this out until we have seen signs of life elsewhere.

Depending on the numbers one plugs into the Drake equation, or variants thereof, the number of intelligent species ranges from hundreds of millions just within the Milky Way galaxy to but one in the entire observable universe. Needless to say, that's a rather sizable range.

If our nearest intelligent neighbor is in the next galaxy cluster, that still leaves room for billions of intelligent species in the observable universe, but it also leaves us essentially all alone. There's essentially no difference between a one-time freak accident where we truly are alone in the universe versus a billion intelligent species in the universe. There would need to be billions upon billions of intelligent species in the universe to have neighbors with whom we can communicate. Are there? The only possible answer science can currently offer is "that's a good question!"

Life here on earth developed on earth as far as scientists are aware. It is believed that life began in nutrient-rich puddles of a mud-like substance that is known as "primordial soup". This was the primitive ocean of the earth. Heat was also needed to develop life, and it's believed that life developed in the mid regions of Africa due to it being the hottest areas of the earth. I don't know about the formation of the cell under these conditions so that's an area I won't be able to explain. But from there, the theory of evolution took over. Cells start forming, mutating, developing some degree of genetic variation. Eventually, after millions of years, multi-celled organisms formed, like plants and basic animals. It's debated whether it was jellyfish or sea sponges that came first. Personally, I believe it's the sea sponge simply because it seems a more simple creature, it's just a bunch of identical cells working together collectively. Then evolution just continues on, creating more and more complex life.

• I think the first multicellular organisms were simple unicellular organisms being glued together. It was a next step as they've started to differentiate for different tasks. For example, if we have a 2-cell being, where the first cell does only photosynthesis, and the second does the biochemical processes, they can be much more effective as if both should do both tasks. | Another possibility, that multicellular life started by that a cell has eaten another, but it couldn't digest it. Probably so were the mitochondrions evolved. – peterh says reinstate Monica May 2 '17 at 17:45