Colloquium: Dr. Carey Lisse, JHU Applied Physics Lab
ABSTRACT: This talk will present the current "big picture" for the formation and evolution of life on Earth, with special attention to its astronomical, geological, and chemical requirements. Astronomically, there are 10^11 stars in our galaxy, each according to the latest Kepler results likely to have formed its own Earth-sized planet. The Universe is 13.8 billion years (Gyr) old, the Galaxy is about 12 Gyr old, our Sun is ~4.6 Gyr old, and high-Z chemical elements took a few generations of stars to form. Sol and our solar system are ~2/3 of the way out from our spiral galaxy’s relatively weak central black hole, in the suburbs so to speak. The Earth itself is a 4.56 Gyr old, highly differentiated, very unique object with all its water on the surface, a giant moon stabilizing its spin, plate tectonics keeping it warm and a shielding magnetic field. Life is found on the Earth in an incredibly narrow spatial range, -20 to +100 km from the surface of a body of diameter ~104 km, and is found only where liquid water is availablewe live, work, & die on the thinnest wet rind of the terrestrial orange. Failed planet harbors for life exist next-door in Venus and Mars.
Historically, the first forms of life appear to have formed in high temperature environments. Earth-life was mainly blue-green and single-celled for the first 3.5 Gyr of the planet’s existence. By ~2 Gyr, in the first massive life-based pollution event in the planet’s timeline, phototrophic plant life had driven the atmosphere out of equilibrium, removing almost all CO2 and converting it in the O2 without which it is likely there would be few animals and no land dwelling creatures. Complex multi-cellular life only arrived after ~3.5 Gyr. Since then, multi-cellular life has gone through at least 4 huge upheavals due to giant impacts. But for these bug-eyed monsters, trilobites, or giant lizards would be ruling the Earth. Creatures even remotely resembling Homo Sapiens have been on the Earth for only ~4 million years (Myr) out of 4.56 Gyr, an ~10-3 duty cycle. Even today bacteria are the most successful forms of life reckoned by total biomass, and we each carry some of this biomass on our skin, in our gut, and in our mitochondria.