Every spring since 1917, Nenana, Alaska, has hosted a contest in which participants try to guess the exact time that a wooden tripod placed on the frozen Tanana River will fall through the breaking ice. Hundreds of thousands of people now enter their guesses on the Internet and vie for as much as $300,000 in prize money. Scientists have also been interested in the contest because a trend to earlier ice breakup times could be evidence of global climate change.