"To a human, two billion years is an unfathomable interval. But that, a team of European, Gabonese, and American scientists now say, is how long ago a recently discovered hoard of fossils suggests Earth’s first big life evolved — large enough to see with the naked eye, and in a spectrum of forms that tease and bewilder. What do their shapes mean? Would the life that existed on 2-billion-year-old Earth have given us any clues to the Earth we see today? Just what were these things?" - Mark H

"To put the unexpectedness of this fossil cache in perspective, consider that Earth condensed out of the planet-forming gas disk that shrouded our young sun about 4.5 billion years ago. Life evolved surprisingly swiftly after Earth’s birth, probably by 3.5 billion years ago and perhaps more than 4 billion years ago. But the ancestors of the large life forms we see today did not appear until the Cambrian Explosion, about 550 million years ago, and the first large life, the Ediacaran Biota, appeared just 50 million years before that, ca. 600 million years ago (relatively simple but macroscopic branching algae may, however, have evolved as early as 700-800 million years ago). These new fossils nearly split the difference and represent a mind-boggling 1.5 billion year leap back in time. They appear to have been a surprising punctuation mark in an otherwise monotonous microbial interlude. Of course, the fossil record being as fragmentary as it is, this is not to say it was the only one. Just the only one we know about so far." - Mark H

"So what might have encouraged this early flirtation with bigness? Immediately prior to their evolution, atmospheric oxygen spiked during the Great Oxygenation Event of 2.3 billion years ago, a result of the invention of photosynthesis by cyanobacteria and the running out of iron deposits with which to sop all the resulting oxygen up by rusting out (the genesis of the famous banded iron formations in Minnesota and Western Australia). This is consistent, the authors say, with the idea that more fuel in the form of oxygen allowed the evolution of bigger life forms. Aerobic respiration of the type made possible by oxygen yields 15 times more power than anaerobic respiration, and all this extra power could fuel bigger bodies, some have hypothesized. Intriguingly, these creatures disappeared around the time atmospheric oxygen levels nosedived, where the oxygen concentration stayed for the remainder of the Proterozoic Era up to about 800 million years ago, just before big life went mainstream in the Ediacaran/Cambrian. Although the idea that oxygen levels determine how big and complex life can be is “not universally accepted as a major driver for the evolution and complexification of multicellular life”, this evidence tends to support the idea, these scientists say." - Mark H