Jon Kopaloff/Getty; Brooke Shields/Instagram Brooke Shields
In honor of the annual celebration, which marks the start of the environmental movement in 1970, the actress posted a throwback shot of herself enjoying nature in the nude.
"This Earth Day, I'm joining @NatGeo in sharing one of the places on the planet that matters most to me," Shields, 55, captioned the shot, which showed her striking a pose with her back to the camera while surrounded by water and the sunny sky.
"Celebrate your love for the planet with us by sharing a spot you care about," she added.
Shields' latest post came one month after she last shared an update on her recovery process after breaking her femur in late January.
"I've come a long way since this, but the journey is just beginning," she wrote in the March post, which included pictures of her heavily-bandaged arm and right leg and a photo of her sitting with a walker.
Brooke Shields/Instagram Brooke Shields
Shields broke her right femur after falling off a balance board at a gym, she previously told PEOPLE.
"It felt like it was all in slow motion. And then I just started screaming," she said. "Sounds came out that I've never heard before. The pain was so excruciating."
Once at the hospital, Shields underwent immediate surgery to place two metal rods near her hip — and soon needed a second surgery after a broken part of her right femur popped out. Then, after the Lipstick Jungle star was able to go home, she developed a severe staph infection, which required emergency surgery and multiple blood infusions.
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Since returning home again, Shields has started relearning how to walk.
"For the first time in my entire life, I thought, 'I can't power through this,' " she said of the healing process. "I can't even stand on my leg or go up a step."
However, Shields says that the struggles she's faced throughout her career have prepared her for what lies ahead. "I'm the only one that's going to be able to get through this," she said. "My career has actually been like that as well. One door gets slammed in my face and I search for another."