To the question, What part of a star's habitable zone has the best chance of developing life?, I made the following comment:
It's always intrigued me as to why some people have thought that life in our solar system might have developed on Mars before transferring to Earth, via meteor impacts. Mars is farther from the Sun & is colder. Also, in the early days of the solar system, the Sun's energy output was less than what it is now, implying Mars would have been even colder than it is now.
To which @ProfRob made the comment:
Mars had an atmosphere and was warmer and wetter in the past, & a thicker atmosphere I should say
I accept all of this, but my question now is, what where conditions like on Earth when Mars was warmer, wetter and had a thicker atmosphere? Could life have evolved here first or was Mars a better candidate for life to develop on first?