re: Maximum Number of Habitable Planets at the Time of Earth's Origin: New Hints for Panspermia?
We find that there was a maximum number of habitable planets around the time of Earth's origin. If at all, interstellar panspermia was most probable at that time and may have kick-started life on our planet.
Interesting.
I'd speculate that they're saying that earlier eons of starburst had previously seeded the galaxy with more main sequence stars of appropriate heavy metallicity (stuff heavier then helium) such that a max # of planets were around. Then, if life started somewhere, there was a higher probability that another infant Earthlike receptical was a minimum # of LY away.