Planetary Habitability at twelve to seven billion years ago
Following this question, I had additional question of habitability. Assuming that life could exist on planet formed roughly twelve billion years ago, allowing complex life to exist as of seven billion years ago, what would be the most plausible explanation of how they survived from:
Given the much, much higher gas densities of the era, I'd be far, far more worried about getting blasted apart by the numerous supernovas popping all over the place, and black hole radiation blasts from the super-massive central black hole and actively feeding nearby black holes. Each of these might be sufficient on its own to sterilize areas ranging from dozens of light years for a supernova to perhaps a whole galaxy for the central super-massive. Plus rare events like a triple neutron star collision, etc. - Serban Tanasa's answer
To keep the question in narrow term,
- How does the star system (that hosts the planet) survive or protect its planets of those dangerous radiation sources?
- If the above condition is impossible to meet, how could a planet protects its life from such radiation? 2.1 Is it possible for life to evolve underground during the early era, and later (at seven billion years ago) populate the surface? 2.2 Is life in an ocean environment similarly affected by the radiation? Or could they survive?
- And finally, if all of the above requirements were impossible, could life itself have evolved in a way that that could resist radiation?
Answers do not have to cover all of the questions above, you should just move to next questions if previous question(s) were deemed impossible.
I'm expecting that the evolution of life on that planet follows similar path as of earthen life, like:
- RNA life at first,
- Cellular life,
- There would be a Great Oxygenation Period to fill the atmosphere with oxygen,
- And complex life evolved a a later time (similar to Earth's Cambrian period)
Of course it doesn't have to be on that sequence, and the answer could be more flexible.
This post was sourced from https://worldbuilding.stackexchange.com/q/12897. It is licensed under CC BY-SA 3.0.
1 answer
Couple ways it could work:
Magnetic fields
The planet could have a really strong magnetic field. Earths magnetic field protects us from a nuclear furnace that's relatively close by.
Likewise, the sun has a magnetic field which would offer some protection.
Water
Some theories say that early earth was protected from radiation by a shield of water. Being deep underwater for the first billion years or so would also help. Maybe forming around nutrient rich underwater volcanos.
Nebula/Molecular clouds
Gasses could absorb some radiation. A stellar nursery is a molecular cloud where stars are forming, possibly with a planet.
Boring neighborhood
By shear chance the star forms in the most boring part of the galaxy, where nothing much is happening. Considering how many things have to not go wrong for evolution be possible, it seems like a miracle that our world isn't a lifeless rock.
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