From Pachyderms to Cetaceans, the largest mammals on Earth would arguably never have evolved to their gargantuan sizes without the third most abundant element in the Cosmos --- Oxygen.  Of course, life, even photosynthesis is possible without Oxygen, but for the cosmos to evolve the big-headed space aliens of our sci-fi dreams will likely take Oxygen --- the most efficient energy carrier in the periodic table.  How Oxygen became dominant on our own planet is the focus of today’s episode with guest Timothy Lyons, a biogeochemist at the University of California, Riverside.