To celebrate the 40 anniversaries of World Earth Day on April 22, the International League of Conservation Photographers (ILCP) selected "40 Best Nature Photographs of All Time."

The collection of 40 pictures, many of which will be on sale as part of Christie's first "Green Auction" in New York to mark Earth Day, stretches across more than 100 years of photography.

Following are the top 10 photos among them:

"Polar Dance" by Tom Mangelsen [sci.sina.com]