Chris Peterson wrote:BDanielMayfield wrote:I have to admit that what Doum has just shared about the GRB hazard in the early universe sort of cancels out the point I was attempting to make. Fermi's Paradox asks us to find reasons why we appear to be alone in the universe. Even though planets have been around for a very long time, SAFE planets evidently are a more recent development.
I'm skeptical. If Earth is any indicator, life is very robust. Major extinction events still leave plenty of life, possibly stimulate mutations, and certainly open up lots of new niches. Sea life in particular should be quite resilient to GRBs.
I suspect that the resolution to the Fermi Paradox has a lot more to do with the incidence of technological species than of life itself.
I'm still of the completely subjective opinion that advanced life is rare in the universe. The reason for my belief is that there are so many factors that have gone into making advanced life possible on the Earth. There is the well-behaved (and more-massive-than average) star, there are the nice relatively circular orbits of the major planets, there is the fact that the Sun has no companion, the fact that it is a slow rotator and has a very adequate but not violently flaring magnetic field, there is the fact that the Earth has its own robust magnetic field (in contrast to similarly-sized and almost similarly-massive Venus) to protect its atmosphere, there is the fact that the axis of the Earth is tilted by about 25 degrees, so that our planet has seasons and escapes the fate of getting relentlessly hot in certain places and incredibly cold in others, there is the fact that the Earth has plate tectonics that continually recycle material on its surface, there is the fact that the Earth has the perfect amount of liquid surface water (which means that the Earth has both oceans and land masses), there is the fact that the Earth has a water precipitation cycle, there is the fact that the Earth has maintained a relatively constant temperature and the presence of liquid surface water (except during its Snowball Earth phase) for most of its four and a half billion year existence.
And of course, there is the unexplained and perhaps just lucky or random emergence of complex life forms some 650 million years ago or so. And there is the perhaps equally lucky or random much later emergence of a species that could both think, speak, cooperate and manipulate its surroundings with its own body.
So many things could have gone wrong here. I still think it is very unusual that all these positive factors are present at the same time in any planetary system to create such benign conditions for life and, not least, for fragile advanced life. But I agree with Chris that simple life forms are likely to form much, much more easily, and that they may be present on (or more likely below the surfaces of) many planets.
Then again, I don't think it was these little critters that BDanielMayfield was talking about, or that it was bacteria-like life forms that Fermi referred to when he formulated his paradox.
Ann