Nasa asked social media users to post pictures of themselves on Tuesday under the hashtag #GlobalSefie.
Photos tagged with #GlobalSelfie on Twitter, Instagram or Google+ or posted on Facebook or Flickr will show up on the agency's social media feed in May.
"While Nasa satellites constantly look at Earth from space, on Earth Day we're asking you to step outside and take a picture of yourself wherever you are on Earth," the agency said on its website.
Earth Day is celebrated on 22 April.
This year's Earth Day focused on green cities, according to the United Nations.
More than 1 billion people in about 190 countries were set to take part in events to promote healthier and more sustainable cities.
"Let us care for Mother Earth so she can continue to care for us," UN Secretary-General Ban Ki-moon said.