One of southern California’s oldest giant sequoias holds more leaves than there are people in China. It has stood since there were fewer people on Earth than live in modern Japan—more than 3,000 years. It was a seedling hundreds of years before Aristotle began tutoring Alexander the Great—and it is still living today.

In the Hoh Rainforest on Washington State’s Olympic Peninsula, towering above mushrooms and damp ferns, are green, moss-draped spruces and hemlocks that were alive in the late 1500s “when Sir Francis Bacon and Johannes Kepler first recognized the value of objective data over mystical portents,” scientist Jerry Franklin and his co-author, Ruth Kirk, wrote in The Olympic Rain Forest: An Ecological Web. Those trees “have been pushing their