Our habitat is a spheroid mostly made up of iron, oxygen, silicon, and magnesium that masses about 6.6 sextillion tons. Seventy-one percent of its surface is covered with water, and its surface temperatures can vary by more than 260 degrees Fahrenheit. Earth’s gravity holds us to it even as it spins us at about 1,000 miles an hour. It provides us with air to breathe, water to drink, soil in which to grow crops, and wood, stone, and clay to build our shelters.
For much of human history, we didn’t really know how lucky we are. Many ancient cultures, including Greek, Persian, Tibetan, Buddhist, and Hindu, thought of small-e earth as one of the basic elements. It was the solid one: reliable, maybe a little dull. Earth has also long been seen as a mother, giver, sustainer. There was uncertainty, from phenomena like earthquakes and volcanoes, but generally speaking you could rely on earth to be there for you.
Humans have known for a long time that there was more than the earth beneath our feet—that there was, in fact, a big-e Earth—but it took a while before we figured out our place in relation to the sun and stars. Then space travel allowed us to see our whole home, surrounded by dark nothingness.
Humans have now mapped the universe out to 2 billion light-years, but Earth is still the only place known to harbor life. “It used to be said that Pluto is a misfit,” said Alan Stern, the leader of NASA’s New Horizons mission to the Pluto system and the Kuiper Belt. “But now we know Earth is the misfit.”
We have learned that we can change the Earth in major ways—unintentionally and unpredictably. Two centuries ago the deforestation of the east coast of the U.S. resulted in sediments washing down to fill the flood plains of rivers and the creation of coastal marshes. On the other hand, dams and reservoirs are holding back so much dirt that the Mississippi delta is now starved of sediment. At this point, human activity has added billions of tons of carbon to the atmosphere, raised global temperatures and sea levels, and increased the acidity of the ocean.
Every day, we unthinkingly count on the Earth to hold us up, but its long-term reliability now seems questionable. Type “Earth” into a Google search, and the second most frequent question is, “Is Earth gonna be destroyed?”
“Geological epochs conventionally end with some sort of great catastrophe, often an extinction event, right? Extinction events are the great horizon lines,” says Jared Farmer, Professor of History. “And I guess I’m much more interested in thinking about long durations of time and imagining a future without the end of the world.”
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