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This paper makes a lot of assumptions about the nature of life. Just off the top of my head, it takes as given that: a) organisms are sensitive to UV radiatio

This paper makes a lot of assumptions about the nature of life. Just off the top of my head, it takes as given that: a) organisms are sensitive to UV radiation b) atmospheric ozone is the mechanism that protects the host planet against excessive UV radiation c) the planet's atmosphere contains lots of nitrogen d) the planet has large oceans of water (since the paper notes the main significance of high UV flux would be to kill off marine plankton) These all hold true for Earth, but not for places like Europa or Titan, let alone more exotic environments.

guelo 12y ago
From the paper: "While life can take numerous other forms and could be much more resilient to radiation than on earth, we make here the conservative assumption that life is rather similar to the one on Earth. This common assumption is the basis for searches of Earth like exoplanets as places that harbour life. "
- happyscrappy 12y ago
  There are creatures that are resilient to radiation already on the earth. http://en.wikipedia.org/wiki/Tardigrade http://en.wikipedia.org/wiki/Tardigrade
  - maaku 12y ago
    Right, but these are the exceptions for a reason. Something life is exposed to only every hundred(s) millions of years or so is so infrequent that evolution selects against so long as it introduces inefficiencies (and nothing is free). Evolution is an extremely dumb optimization process, and will simply drift away from rad-protecting features as soon as the event is over.
    - deleted 12y ago
      [deleted]
    - dandelany 12y ago
      True, in places where the only sources of radiation are rare events like GRBs. But I imagine there must be hospitable exoplanets somewhere in the universe that are, for one reason or another, subjected to more intense radiation constantly, in which case rad-protection would have a strong impact on evolution
Retric 12y ago
Marine plankton created the ozone layer by turning CO2 into O2 which could then be transformed into O3 (Ozone). Which suggests plankton don't really need an ozone layer.

guelo 12y ago

From the paper: "While life can take numerous other forms and could be much more resilient to radiation than on earth, we make here the conservative assumption that life is rather similar to the one on Earth. This common assumption is the basis for searches of Earth like exoplanets as places that harbour life. "

happyscrappy 12y ago
There are creatures that are resilient to radiation already on the earth. http://en.wikipedia.org/wiki/Tardigrade http://en.wikipedia.org/wiki/Tardigrade
- maaku 12y ago
  Right, but these are the exceptions for a reason. Something life is exposed to only every hundred(s) millions of years or so is so infrequent that evolution selects against so long as it introduces inefficiencies (and nothing is free). Evolution is an extremely dumb optimization process, and will simply drift away from rad-protecting features as soon as the event is over.
  - deleted 12y ago
    [deleted]
  - dandelany 12y ago
    True, in places where the only sources of radiation are rare events like GRBs. But I imagine there must be hospitable exoplanets somewhere in the universe that are, for one reason or another, subjected to more intense radiation constantly, in which case rad-protection would have a strong impact on evolution

Retric 12y ago

Marine plankton created the ozone layer by turning CO2 into O2 which could then be transformed into O3 (Ozone). Which suggests plankton don't really need an ozone layer.