Comment by eru
6 days ago
Also more importantly: it was uniformly warm. No gradients.
Life on earth doesn't work because we get energy from the sun. It works because we get low entropy energy from the sun and can radiate high entropy energy into cold space.
(There's approximately no net energy inflow.)
You are right about gradients, but while the energy from the Sun is what sustains most of the life today, it played no role in the appearance of life (because capturing solar energy requires exceedingly complex structures).
For the appearance of life it is necessary for the planet to have a much warmer interior than its surface (i.e. a radial gradient of temperature). In that case, volcanism and related phenomena bring to the surface chemical substances that have formed at higher temperatures and which are no longer in chemical equilibrium at the cooler planet surface, providing the chemical energy for the synthesis of the complex organic substances.
Some bacteria and archaea (belonging to the so-called acetogens and methanogens) still exploit the inner heat source of the Earth, living completely independently of the solar energy, in the same way like the first living beings. (However, in many popular science publications one can see frequently wrong claims about various organisms, including some animals, that they do not depend on solar energy, but those claims are false, because those living beings depend on using free oxygen for the oxidation of various substances, like hydrogen sulfide from oceanic vents, and the free oxygen comes from algae and plants that have used solar energy to separate it from water.)
> You are right about gradients, but while the energy from the Sun is what sustains most of the life today, it played no role in the appearance of life (because capturing solar energy requires exceedingly complex structures).
Yes, agreed!
My point was merely that the lukewarm phase of the universe didn't really have easily available temperature / energy gradients available. Even though the temperature itself was fine, but that's not enough.