A planetary clock scientists say has already started.
Every breath on Earth depends on a delicate balance that has quietly held for hundreds of millions of years. Yet scientists now say that balance is temporary. Research supported by NASA suggests the oxygen rich atmosphere that sustains forests, oceans, animals, and human civilization will not exist forever. Far in the future, subtle changes driven by the aging Sun will begin altering the chemistry of the sky itself. Carbon dioxide will fall, plants will disappear, and oxygen will slowly fade from the air. Long before the planet dies, Earth could transform into a world that looks strangely familiar to its distant prehistoric past, but unrecognizable to us.
