Sentient planets
To an extent, Earth is a living planet, as biological beings do indeed swim, crawl and fly through our world's uppermost layers of ocean, land and sky. But all that is still a far cry from the literally living, conscious planets that make appearances in many sci-fi and fantasy stories. Take the living planet Mogo in "Green Lantern," which can change its climate and grow foliage in desired patterns on its surface at will.
Or consider
the moon Pandora from the 2009 film "Avatar," where flora and fauna have evolved tentaclelike organs that enable them to neurally interlink with each other. A globe-spanning consciousness exists, with Pandora's trillion interconnected trees acting like cells in a colossal brain, dwarfing our mind's 100 billion neurons.
In reality, the development of a planet-scale "being" looks to be an extreme long shot. Based on the chemistries and behaviors of life and nonlife, don't bet on Mogo or Pandora, scientists say. "The way evolution works, I can't see it happening," said Peter Ward, a professor of paleontology at the University of Washington.