Earth Day offers the perfect opportunity for eco-minded charities and organizations boost fundraising and awareness. This year, though, Edward Norton and CrowdRise, his crowd-sourced fundraising site, are hoping a little friendly competition can do even more good. Norton and CrowdRise, along with social saving site Groupon, are offering an additional $50,000 to the three green causes that can raise the most money online.

Organizations making a play for the prizes — as well as an influx of Earth Day-inspired donations — include Conservation International, Global Green, the Conservation Lands Foundation, the Ian Somerhalder Foundation, Friends of the Virgin Islands Nation Park, Wiser Earth and the National Wildlife Humane Society. While it may not be nice to play favorites among organizations trying to help the planet, the campaign that raises the most money May 15 will receive an additional $25,000, with the second-highest earner getting $15,000 and the third-highest pulling in $10,000.

The rise of social media has given way "crowd-funding," to a new form of fundraising that artists and filmmakers have been making great use of on sites like Kickstarter and Indie Go-Go. The theory goes that in the age of Facebook and Twitter, it's easier to get a lot of people to each donate a little money than vice versa. In 2010, Norton and friends realized the same idea could work for charities, effectively eliminating a lot of the unnecessary costs that keep charities from making the most of their donations.

“I think it's very clear that figuring out how to live sustainably within the environmental systems that support us is the defining challenge of our era,” says Norton, who is also a U.N. Goodwill Ambassador for Biodiversity. “Earth Day is important because it's about waking up more people to that challenge and committing to engage in it ourselves.”

A full list of causes competing, plus links to other green charities, can be found at http://www.crowdrise.com/EarthDay2012