muso wrote on Aug 29^th, 2013 at 6:57pm:


Not a definitive  signature for life because there are other non biological sources for molecular oxygen to build up in a planets atmosphere

Astrobiologists prefer to look for sustained and constant methane presence in an planet's atmosphere - a far stronger signature for life because methane breaks down relatively quickly in the atmosphere (its decomposition half life being about 14 years)

if you find methane, even in low concentrations AND molecular oxygen in the planets atmospheric that combined evidence tells us there is some sort of sustained biological process occurring on the planets surface/oceans etc

Chimp_Logic wrote on Aug 29^th, 2013 at 7:13pm:


You're right with oxygen, but there are all kinds of ways methane can be produced. I'm thinking particularly of Carbon dioxide/ water ices on Mars. These usually have bubbles in them which capture  the atmosphere (mainly nitrogen). Bombard these with energetic particles from the sun (mainly high energy protons), and you get free radicals which can recombine to form methane, formaldehyde, oxygen, ozone,  ammonia and just about any simple molecules that contain Carbon, Hydrogen, Oxygen and Nitrogen.

The polar ice caps of Mars are continually sublimating and reforming depending on the season. Traces of these substances are released almost continuously.   

Then there is photolysis of the CO2 in the atmosphere by UV.

Titan (the largest moon of Saturn) has an atmosphere containing methane (1.6%) and ammonia.   

Astrobiology always strikes me as a highly speculative deductive process based on very little evidence.

The trouble is that speculation doesn't come with error bars.

In line with your signature, we need to submit it to some skeptical scrutiny.

The latest evidence shows a thick oxygen rich atmosphere on Mars up to about 4 billion years ago. Prior to 4 billion years, there was probably surface water,and there is some evidence of water at neutral pH (montmorillonite)

At about 4 billion years bp, a body about the size of Pluto flew past and ripped away most of the early Martian atmosphere. Since that time there has been a tenuous atmosphere where volcanic offgassing is balanced by loss of atmosphere to space.

So far so good. What was the receiving environment like on Earth around this time? Well, prior to 4 billion years bp, the Earth was in the Hadean period of the Pre Cambrian.

It was about this time that a body the size of Mars collided with the Earth forming the Moon. Sometime within that 500-600 million year period you have to fit in the initial cooling and formation of the Earth's crust (250 million years should do it ) then you need another 100-200 million years after the collision that formed the moon, so it doesn't give us much of a window for life to be established.

In short, it was not a very hospitable receiving environment.

See what I mean?

It's a very seductive idea, that of life originating on Mars, but there are too many sequential low probability events.

I don't know what they're going on about with respect to Molybdenum in a high oxidation state, but there was so much banging and crashing going on in this era, that it could have come from anywhere.  For that matter, how do we know that the Molybdenum salts didn't arrive on Earth from Mars and initiate the abiogenesis here on Earth?  It's much more plausible given the toasty interplanetary environment of the early solar system.

I have a contact at Manchester University. He's an expert on carbonaceous chondrites. I might contact him to get a heads up on the latest research in that area. 

If microbes adapted to a high oxygen environment on Mars had impacted on the Hadean Period Earth, how successful would they have adapted or even survived in the new environment?

The other problem with the Martian abiogenesis theory is that it requires nutrients on Earth to allow survival and reproduction of those organisms. 

The problem is that we don't really hold many of the early jigsaw pieces, and there are a lot of low probability events.  All we have is a lot of assumptions and too many degrees of freedom for a viable solution.

Do we know how many times life started? Was it only once?

A couple of very old questions I noticed:

freediver wrote on Jul 4^th, 2010 at 11:10am:

Well, the one that's normally brought up is deinococcus radiodurans. It is understood that it evolved within the cooling systems of nuclear reactors from other bacteria. (Anecdotal only) Halobacteria require light as an energy source for producing ATP. They are usually found in salt lakes and are quite primitive. They are archaeans - they have no nucleus or organelles, but if our first organism lived in the dark underground soup, then halobacteria are less likely candidates.

Quote:


Smaller simple organisms tend to survive heat (and radiation) better than larger organisms. The simpler they are, the less there is to go wrong.  (if you see what I'm driving at)

Probably too big.

Surely if we believe that life evolved here on earth just
from the normal interaction of molecules in water then
it had enough time to evolve on Mars?

If so then we must be almost 100% certain that evidence of life will be found on Mars -
it's normal & natural for it to happen!