Older Alien Worlds May Still Be Stuck in the Slime Age

A new paper in the International Journal of Astrobiology by Dr. Christopher Doughty of Northern Arizona University proposes using a planet's net primary production (NPP) — the carbon photosynthesis converts into organic matter each year — instead of stellar age to gauge how evolved its life might be. Among 29 confirmed rocky exoplanets, K2-3d ranked highest at 1.74 times Earth's NPP and GJ 1061c at 1.03, while TRAPPIST-1e was deemed a poor candidate for complex life.

• Before the Cambrian explosion, Earth's biosphere fixed about 2.4x10^25 grams of carbon
• By the arrival of humans that figure had grown to 9.4x10^25 grams
• K2-3d, 143 light years away, has an NPP 1.74 times Earth's
• GJ 1061c, 12 light years away, reaches 1.03 times Earth's NPP at about 7 billion years old