According to this report, the galaxy has billions of potential earths:*
But, based on the limited numbers of planets found so far, Dr Boss has estimated that each Sun-like star has on average one “Earth-like” planet.
This simple calculation means there would be huge numbers capable of supporting life.
“Not only are they probably habitable but they probably are also going to be inhabited,” Dr Boss told BBC News. “But I think that most likely the nearby ‘Earths’ are going to be inhabited with things which are perhaps more common to what Earth was like three or four billion years ago.” That means bacterial lifeforms.
It’s an interesting idea, but it is an example of carbon chauvinism. If we’re looking for lifeforms, we should be open to the possibility that life out there doesn’t conform to our carbon-based history or expectations. When we explore other planets, instead of looking under the rocks, maybe we should be looking at them.
In related news, a biogeek asks Where is my silicon-based life?
Silicon is the most abundant element (barring oxygen) in the earth’s crust. If silicon is so chemically similar to carbon and it’s so readily available, why aren’t we silicon-based? Silicon is routinely used by carbon-based lifeforms, but while (for example) diatoms (a type of algae) make their cell walls out of silica, carbon in is the backbone of their DNA, their proteins, and the basis of their biochemistry. Silicon is just along for the ride.
The answer involves subtle differences between carbon and silicon chemistry. While carbon and silicon can theoretically form very similar kinds of structures, complicated carbon-based molecules tend to the stable, while complicated silicon-based molecules tend to fall apart (especially in water).
There’s a major waste disposal issue as well – carbon dioxide is a gas, and silicon dioxide (sand) is a solid. When we metabolize oxygen, we produce carbon dioxide as a waste product, but it dissolves easily in our blood for rapid waste management. If, on the other hand, we produced sand internally with every breath, chaffing would be the least of our worries. Most silicon molecules also lack chirality (or “handedness”), which is a hallmark of terrestrial carbon-based life, but not necessarily a deal-breaker.
I won’t go so far as to say that there’s no such thing as a silicon-based biochemistry. As Arthur C. Clarke said, “When [a distinguished and elderly] states that something is impossible, he is very probably wrong.” Being relatively young and almost completely undistinguished, my odds would be even worse. I will say that, if a silicon-based biochemistry exists, it probably doesn’t use silicon the way we use carbon, and we might even have a difficult time recognizing it as life (unless it mind-melds with Spock).
However, silicon-based lifeform based on a simulation of carbon-based life could be a possibility….
[* link thanks to Alan Sullivan]