The Charmed Life of Planet Earth
History - World Released - Apr 09, 2016
The Earth has been on an amazing journey since its creation 4.5 billion years ago, something I learned about from watching the History Chanel. To find out more I purchased the book that was recommended: “Rare Earth: Why Complex Life is Uncommon in the Universe,” by Peter D. Ward and Donald Brownlee. The book covers the same story but in greater detail, with particular emphasis on the origin of life, from basic microbial life to complex animal life, to highly intelligent life capable of conscious thought, to homo sapiens--us. Are we really the stuff of stars, as Carl Sagan said? How does the most elementary particles—released in the Big Bang—evolve over time and produce brain cells capable of rational thought, indeed, of being able to contemplate the origin of universe? That question goes unaddressed in “Rare Earth.” It is the 600-pound gorilla in the room, with vast implications well beyond the scope of the book.
The premise of “Rare Earth” is that microbial life is common throughout the universe while animal life is extremely rare. How can that be? Because microbial life—life in its most basic form—is incredibly hardy. It can withstand extreme temperatures (from well below freezing to above the boiling point of water), incredibly high pressure, does not require oxygen to exist, and in some cases does not require sunlight. The authors believe that microbial life may not have originated on Earth, but may have been transferred here by comets, or possibly by asteroids that originated on a neighboring planet, probably Mars. Animal life, on the other hand, is fragile. It can only survive in an atmosphere of plentiful oxygen, lots of water, minimal planet disruptions, and Goldilocks’ temperatures—not too hot and not too cold. Microbial life arrived not long after earth’s formation and survived countless planet disruptions that would have vanquished more complex animal life. Thus, for the first 2.5 billion years, while the surface of Earth was unstable and noxious, microbial life was the only life that could survive.
Since then, during the two billion years it took for animal life to emerge and evolve, Earth enjoyed a charmed existence. It was neither too close nor too far from a large stable sun, had a circular rather than elliptical orbit, was protected from astroids and comets by outer gas giants (“cosmic vacuum cleaners”), particularly Jupiter, and likewise was protected from ultra-violate rays by a strong magnetic field, thanks to Earth’s mostly iron core. During a portion of this time Earth and sky were transformed by the introduction of oxygen, while at the same time continents formed made of relatively lightweight and highly durable granite, which more or less floated on heavier molten rock. The floating continents, coupled with a few active volcanoes, helped regulate Earth’s temperature and insured that the planet surface was continually being recycled. Add a generously large moon to regulate the tides, with the earth tilted on its axis just so to create seasons and further regulate temperatures, and Earth became a veritable paradise, a garden of eden.
Still, all was not ideal. Over time, there were a few well-placed catastrophic events that destroyed all but the smallest and most adaptable forms of life. The most recent was a large asteroid or comet that struck earth 65 million years ago putting an end to the age of dinosaurs. A good thing, too, because with dinosaurs around mammals didn’t stand a chance of evolving into larger creatures, such as sheep, cattle, horses, apes, and, as late as 50 thousand years ago, homo sapiens. These catastrophic events, while rare, served as a reset button—an occasional re-shuffling of the order of life on Earth—without which man could not have evolved. There are many more dimensions to Earth’s charmed existence, including its location on the outer edge of the Milky Way galaxy, shared with a few stable stars in the immediate galactic neighborhood, the presence of the right amount of carbon (neither too much nor too little), an iron rich planet composition, and eons of relatively uninterrupted time for life to emerge from the primordial ooze, develop into animal life and, with a few hiccups, produce intelligent life cable of speech, creativity, and conscious thought.
All of these things must happen in order for a planet to produce complex animal life—an amazing string of events threatened at every turn, yet somehow defying the odds not merely to survive but thrive. What are the odds? Thirty years ago, Carl Sagan said there were as many as a million planets in our galaxy capable of producing life. We have learned a great deal since then, including our first observations of distant solar systems with circulating planets that neither look nor act anything like our own. The authors conclude its probable that microbial life is common throughout the universe while a stable and long-lasting environment necessary for the evolution of animal life may not be—hence the rarified and charmed existence of Earth. Are we alone? While the odds have been significantly reduced since Sagan made his prediction, the jury is still out.
- END -