North America

Thomas Jefferson once advocated the idea that European culture was making North America's climate pleasantly warmer.

• By Francie Diep

Until recently, the reigning theory on who the first Homo sapiens in North America were pointed to the Clovis people, evidence of whose culture was discovered in the American Southwest. That theory has been powerfully challenged by, among others, Meadowcroft, an archaeological dig in western Pennsylvania that began in the 1970s.

• By Steve Moyer