Image: Time windows for complex and microbial life on Earth analogue planets orbiting Sun-like stars (F(7), G and K(1) stars) during their main sequence lifetimes. Assuming that the processes leading to multicellular life are the same as on Earth (i.e. 1 Gyr for life to emerge and 3 Gyr for multicellularity to evolve), the potential lifespans of a more complex, multicellular biosphere are estimated. Multicellular life was assumed able to persist until surface temperatures reach the moist greenhouse limit for an Earth analogue planet in the continuously habitable zone of the star-type in question. Microbial life is then assumed to dominate until either the maximum temperature for microbial life is exceeded, or until the star leaves the main sequence (whichever happens first). The average age of Earth-like planets was found by Lineweaver (2001) to be 6.4 +/– 0.9 Gyr based on estimates of the age distribution of terrestrial planets in the universe. This average age falls within microbial and uninhabitable stages for G and F type stars respectively, but falls within the multicellular life stage for K stars.
Credit: Jack T. O’Malley-James.

G-Class Outliers: Musings on Intelligent Life


Because I had my eyes dilated yesterday afternoon en route to learning whether I needed new reading glasses (I do), I found myself with blurry vision and, in the absence of the ability to read, plenty of time to think. Yesterday’s post examined a paper by a team led by Jack T. O’Malley-James (University of St Andrews, UK), addressing the question of how our planet will age, and specifically, how life will hang on at the single-cell level into the remote future. It’s interesting stuff because of its implications for what we may find around other stars and I pondered it all evening.

Have a look at one of the figures from the O’Malley-James paper, which shows the stages a habitable Earth-like planet (ELP) will pass through as it ages around main sequence stars. I also clip the caption directly from the paper.

Read more: G-Class Outliers: Musings on Intelligent Life — Centauri Dreams.

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