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[Comments] (1) No Fish On Mars: Cool planet, Mars. But does it harbor life? Maybe! Early in its history, Mars had lots of liquid water, and you know what happened when Earth had lots of liquid water--complex multicellular life!

Obviously it's unlikely that complex life is still hanging around Mars, what with the UV and the thin atmosphere and lack of water and everything. But when I put some numbers together in a back-of-the-envelope way, I discovered it's also very unlikely that Mars ever supported multicellular life of any kind, even if you stipulate life on Mars and spot the planet some serious handicaps.

I'm going to show you one of those compressed timelines from the formation of the solar system to the present day. I tried to do a graphic representation, but I screwed it up, and graphs tend to give an impression that your numbers are precise, so here's a textual representation. Below is the text of five items from my Twitter feed. The five tweets and spaces between them add up to 454 characters. As it happens, Earth and Mars are both about 4,540 million years old. So consider each character of this text as representing 10 million years.

One extra wave of sinking nausea per news medium, but I suppose "physical newspaper front page" must be the last of it now.|I didn't get where I am today by having Irish labourers promoted over my head.|beautiful scrambled neologisms from spam today: trfiedy, hdunddrend, asbthma, mevdicinxes, onex, effzective, preventinon, jof|@danielsolis I salute your hair, sir.|Happy birthday @jong, with Milo Murgia and Amy Pond among my alltime favourite gingers!

It is only a matter of time before Twitter-based textual representations are used to bring all cosmic time scales into perspective. "If the history of life were represented as a tweet, all of mankind's achivements would be cut off when it was retweeted."

OK, check it out. Here's the same text, with formatting added to point out important points in the history of life.

One extra wave of sinking nausea per news medium, but I suppose "physical newspaper front page" must be the last of it now.|I didn't get where I am today by having Irish labourers promoted over my head.|beautiful scrambled neologisms from spam today: trfiedy, hdunddrend, asbthma, mevdicinxes, onex, effzective, preventinon, jof|@danielsolis I salute your hair, sir.|Happy birthday @jong, with Milo Murgia and Amy Pond among my alltime favourite gingers!

Planet formation takes about ten characters, up to the space after "One extra". After that point, both Earth and Mars have liquid water. Earth still has water today, but Mars loses its water somewhere around the word "be". Mars has liquid water for about a billion years, the duration of the underlined text from "wave" to "be".

What happened on Earth from "wave" to "be"? Not much! If you really want to suppose an early origin of life on Earth, you could say it started between "physical" and "newspaper" (italicized), but a more conservative estimate is that it started around "must be the"--right around the time Mars stopped supporting life. And if you demand fossils of the organisms themselves, life on Earth didn't begin until somewhere around "today by having".

How about complex life? Eukaryotes show up around "trfiedy". Multicellular life shows up around "asbthma". If you want some cool complex life like the Ediacaran fauna, you need to wait until "Milo". And even those aren't vertebrates.

Mars may have had enough time to evolve life before its oceans disappeared. And once you have life, it's tough to kill it off. But there wasn't enough time for multicellular life to evolve. Multicellular life is really difficult. And although the discovery of single-celled Martian life unrelated to Earth life would probably be the biggest discovery in human history, alien bacteria are not as cool as alien fish.

Obviously this is really imprecise. But no amount of fudging will put multicellular life in the Martian oceans, unless you can explain why Mars got multicellular life in less than 1 billion years when Earth took three times as long. In a work of fiction (such as the one for which I did this research) you might flex your artistic license and give Mars some tube worms or something, but I don't think fish are realistic.

Here's one complication I didn't mention: around "I suppose" there seems to have been an period called the Late Heavy Bombardment, during which there were a lot of impacts on the inner planets. The interesting thing is that the LHB immediately precedes "physical newspaper", which you'll recall contains the first tenative evidence of life on Earth. So, maybe life comes into being immediately (in geologic terms) whenever conditions are right. Maybe the LHB hit the reset button on Earth life, but spared Mars for some reason. Or maybe the LHB brought life to Earth from Mars! Either scenario would give Mars a 50-character head start. That's a lot, but still not enough for fish.

Another possibility is that the evolution of multicellular life is a freak accident which can happen at any time. It took a really long time to happen on Earth, but it happened right away on Mars. I think this is really unlikely. First, Earth has a much bigger surface area than Mars, so the freak accident should have happend on Earth first. Second, I doubt the whole "freak accident" idea. Prokaryotic life didn't spend billions of years sitting around doing nothing. It was evolving really rapidly through brief generations and horizontal gene transfer, creating the machinery that would eventually be co-opted to combine organisms into multicellular colonies.

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Posted by Brendan at Thu May 20 2010 21:50

I enjoyed this, not least because I am reading under the assumption that you had to wait until there was something inoffensive on my twitter stream to get your data.


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