The people who know the most about life on Earth tend to be the most impressed by its staying power.
Harvard professor Andrew Knoll marvels that our planet has sustained life continuously for four billion years — most of its 4.5 billion years in existence. This is not just a matter of location, said Knoll, who is an earth and planetary scientist. Mars and Venus are both in what astronomers would consider a "habitable" zone, getting sunlight in a range suitable for living organisms. Now both are barren (or close to it).
Earth has special features that may or may not be present on many of the other planets detected around the galaxy. Earth's geology helps regulate the climate through the cycling of carbon dioxide. When exposed rocks weather, carbon dioxide gets pulled out of the atmosphere, allowing the globe to cool. When those rocks get covered in ice, the weathering stops, and carbon can build up as it's replenished by volcanos.
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