Conan the bacterium

[JoeP]

OK, this (http://news.bbc.co.uk/2/hi/science/nature/6191197.stm) made me :chuckle::
The best-studied radiation-resistant microbe is Deinococcus radiodurans.

It can withstand several thousand times the lethal dose of radiation for humans, and has been nicknamed "Conan the bacterium" by microbiologists.

Anyway, the news angle is that
a team of scientists argues that the bugs could only have evolved this unusual ability on a planet like Mars.

"Our hypothesis of a Martian origin for radio-resistant bacteria provides an explanation for their ability to withstand ionizing radiation, a trait that appears to be of no value on Earth at any time in its history," the scientists write in Astrobiology.

Sound crackpotty to me ... what do you think?

[ceptimus]

Stupid crackpot scientists! We evolved on Earth, and we've been here a hell of a lot longer than any flash-in-the-pan mammal species!

:bacilli:

[The Lone Ranger]

In fairness, this isn't the first time it has been seriously suggested that life in this solar system may have originated on Mars and then been "transplanted" to Earth.

In the distant past, Mars was much warmer and wetter than it is now. At that time, there were still a goodly number of large chunks of rock floating about the inner solar system and occasionally smacking into a planet with enough force to knock chunks of the planetary crust into interplanetary space. We still get the occasional meteorite landing on Earth that originated as part of the crust of the planet Mars. Famously, one of them had structures embedded in it that looked as if they might have been formed by bacteria.

So, it's entirely possible that bacterial life first arose on Mars, and was subsequently "transplanted" to Earth as a result of a collision that blasted chunks of Mars' crust into space, which later landed on Earth and seeded it with life.


I'm not saying this is likely. Before I'd regard this as likely, I'd want to see some bacteria (either living or fossil) discovered on Mars. If Martian bacteria were discovered, and if they had the same biochemistry as Terrestrial life, that would be a very strong indication that Terrestrial life was actually Martian in origin. (Or, conversely, that life originated on Earth and was subsequently transported to Mars. But that would be much more difficult, given Earth's much stronger gravity.)

Cheers,

Michael

[Crumb]

Couldn't such radiation resistance simply have evolved underground near a source of radiation like uranium?

[The Lone Ranger]

I don't see why not. Living bacteria have been found ten miles down in the Earth's crust.

Cheers,

Michael

[Roland98]

I had a post on this not too long ago, and my commenters are teh smart (http://scienceblogs.com/aetiology/2007/06/dna_schmena.php):

The radiation resistance is apparently an evolutionary side effect. The same mechanisms evolved to allow the creature to survive extremely dry conditions in arid soil, which also break its genome apart.

...which I find a more likely scenario than "had to evolve on Mars" or something along those lines.

[JoeP]

I got Roland98 to post here! Hi Ro!

Re the Martian angle, when will biologists start asking where the life on Mars came from? Presumably it came from a hypothetical planet that later broke up to form the asteroid belt (although afaik that is not a seriously held hypothesis). And life there came from...

Why do people think that saying "life originated somewhere else" is a useful or meaningful statement?

[The Lone Ranger]

I got Roland98 to post here! Hi Ro!

Re the Martian angle, when will biologists start asking where the life on Mars came from? Presumably it came from a hypothetical planet that later broke up to form the asteroid belt (although afaik that is not a seriously held hypothesis). And life there came from...

Why do people think that saying "life originated somewhere else" is a useful or meaningful statement?

I'm not certain I understand your point. Even if it turns out that Terrestrial life originated on Mars, that would just mean life originated on Mars rather than here on Earth. Since Mars was much warmer and wetter in the distant past, this is not inconceivable. No one, to my knowledge, is seriously suggesting that life in our Solar System originated anywhere other than Earth or Mars.*

Most think it originated on Earth, though there are some who think it may have originated on Mars and then been transported to Earth. No one thinks that "life originated somewhere else" is especially useful, which is one reason why scarcely anyone takes the idea of panspermia serious. Of course, if solid evidence is found that life did not originate on Earth, then that just pushes the search back one level. At that point, the question becomes not "When and how did life originate on Earth?" but "When, how and where did life originate?".


The asteroid belt, incidentally, isn't the remains of a planet that broke up. It's thought to be material "left over" from the formation of the solar system that has never coalesced into a larger body. The gravitational influence of Jupiter and -- to a much lesser extent -- Mars prevents the asteroid "rubble" from coalescing. Even if it could do so, it wouldn't be much of a planet to speak of; the best estimate is that if all the asteroids in the Main Asteroid Belt were to come together, they'd form a body only about 1/30th the mass of our Moon.


*More precisely, Terrestrial life is more or less universally agreed to have arisen either here on Earth or on Mars. That does not preclude the notion that there is life elsewhere in the Solar System that arose independently.

In fact, Jupiter's moon Europa is covered by a frozen ocean. There's good evidence that there's liquid water under the ice. As such, given that Europa is likely to have undersea hydrothermal vents like the Earth does (and lots of people speculate that Terrestrial life first arose in hydrothermal vents), Europa is seen as a relatively good candidate for harboring life. In fact, many scientists think Europa is more likely to have life of some sort than is Mars.

Saturn's moon Titan has a thick atmosphere (thicker than the Earth's) with lots of organic molecules in it. Some also see Titan as a possible candidate for extraterrestrial life.



Cheers,

Michael