Biogenesis on other worlds

[SkepticLance]

One of the arguments I have encountered in relation to life on other worlds relates to extremophiles.

 

Extremophiles are organisms that live in extreme environments - usually bacteria or archaeans. They may be found in hot thermal vents, extreme pressures, extreme cold, extreme pH limits, extreme salinities, or even at extreme depths under the Earth's crust.

 

The argument is that, if life on Earth can live in such extreme conditions, then we can expect it to be widespread on other planets, under those extreme conditions. Life on Earth seems to be able to survive anywhere there is liquid water. Can life be found on other worlds anywhere there is liquid water?

 

There seems to me to be a major flaw in these arguments. While life may survive today, after 3 billion years of adaptive evolution, in these extreme environments, would life actually begin in those places? Can biogenesis occur in a range of extreme environments on other worlds?

 

Any views?

[Paralith]

I admit I don't know much about abiogenesis, but it seems to me that perhaps an extreme environment of the right kind could potentially increase the chance of life naturally originating. But I'll defer to people who know more about the specifics.

[SkepticLance]

As a for instance.

 

Recent data from the space probe Cassini shows that the moon of Saturn called Enceladus has a certain geyser activity. There is a possibility that liquid water may be a part of the geyser action. Of course, they may be wrong.

 

However, there is immediately a raft of speculation about maybe finding life on Enceladus.

 

I have no doubt, that if we found liquid water on one of Saturn's moons, and injected a million randomely chosen species of Earth bacteria and Archaeans into that liquid water, a tiny minority would actually adapt, and eventually reproduce and evolve in that new habitat. However, these are organisms with 3 billion plus years of evolution behind them.

 

What is the possibility that an indigenous life form may have come into being, through whatever biogenesis process, on the moon itself?

[DrDNA]

"There seems to me to be a major flaw in these arguments. While life may survive today, after 3 billion years of adaptive evolution, in these extreme environments, would life actually begin in those places? Can biogenesis occur in a range of extreme environments on other worlds?"

 

Yes. It is believed that the enviroments that these extremophiles live in may be similar to the environment that existed on earth about 2 and a half billion years ago. Before the cyanobacteria (or something similar) put a bunch of free oxygen into the atmosphere by photosynthesis.

 

For example, the atmosphere was composed mostly of nitrogen, methane, ammonia, carbon dioxide, and water before it was oxygen rich.

 

It is believed that Archaea and some bacteria evolved in these conditions. They are able to live in similar harsh conditions today; including, very low pH and high heat and pressure. So, it is believed that life may have adapted from what we consider to be an extreme environment to the one we have now.

 

http://www.spacedaily.com/news/life-01zm.html

http://www.sciencemag.org/cgi/content/full/296/5570/1066

[SkepticLance]

To DrDNA

 

Yes, I am familiar with that argument. However, we do not actually know the conditions under which biogenesis occurred. The idea that it was in a high temperature thermal situation is one of a number of speculations. I have seen other ideas expressed.

 

Until we have much greater understanding of the required conditions for biogenesis, should we not refrain from excessive speculation about life appearing on places such as Enceladus?

[Sisyphus]

To DrDNA

 

Yes, I am familiar with that argument. However, we do not actually know the conditions under which biogenesis occurred.

 

Isn't that the point, though? If there are such different plausible hypotheses for how life began on Earth, then it is not a big leap to say that life could probably begin under a variety of conditions. Yes, it is definitely speculation, but speculation is all we have to go on at the moment. Informed speculation itself is not unscientific - it is just part of formulating hypotheses, so we have an idea where to look.

[DrDNA]

To DrDNA

 

Yes, I am familiar with that argument. However, we do not actually know the conditions under which biogenesis occurred. The idea that it was in a high temperature thermal situation is one of a number of speculations. I have seen other ideas expressed.

 

Until we have much greater understanding of the required conditions for biogenesis, should we not refrain from excessive speculation about life appearing on places such as Enceladus?

 

 

I agree to some extent.

But I also remember before thermophillic bacteria were discovered that everyone assumed that life on earth (an elsewhere) must have begun in an environment like we have today. If not oxygen rich, warm for the most part but not too warm, neutral pH, low pressure, no "harmful" sulfides, etc. Then, in the 80s, someone discovered life fluorishing in the thermal vents deep in the ocean, living off really nasty plume gases and solutes. Everyone was shocked. Those critters were thriving at great pressures, great temperatures, low pH, very very harsh conditions where it was thought that life could not exist. Then many scientists came to terms with the fact life probably began under such conditions, because it was known that the environment on earth must have been similar billions of years ago. Maybe those "harsh" environments were even better for biogenesis than our "gentle" environment.

 

So, in the very recent past, the excessive speculation that you mention was directed at finding life in "gentle", not harsh environments.

 

I guess the take home lesson is we should keep our minds open as to what types of environments we might expect life to begin and evolve in.