/ Source: NBC News
It's the 45th anniversary of Earth Day, and politicians and celebrities alike marked the day on Twitter.
Astronauts shared their view of our big blue world from space, President Obama traveled to the Everglades with Bill Nye, and Ellen DeGeneres encouraged us to wash a tree. There had been more than 570,000 Earth Day-related tweets posted by noon Eastern Time on Wednesday, according to the social network.
