The 84th Annual Academy Awards once again played host to Livia Firth's groundbreaking Green Carpet Challenge focused on susainable and ethical fashion. Unlike previous years, where Firth was the lone representative, the red carpet hosted more than four participants, with one actress being a huge last-minute surprise. 


"So excited to announce," tweeted Firth from her limo last night. "Meryl Streep is in green Lanvin for the Oscars!!"


One of the biggest stars ever to participate in the challenge, Streep stole the red carpet in a gorgeous full-length gold gown made with eco-certified fabric sourced with help from Firth and her team. If that wasn't enough, the Green Carpet Challenge was further elevated when the 62-year-old won the Best Actress award for her role in "The Iron Lady."


"When they called my name," she joked, "I had this feeling I could hear half of America going, 'Oh no! Oh come on, why her? Again!'"


It was Streep's third Oscar win in 17 nominations. 


Naturally, Firth also took to the red carpet in an impressive sustainable red gown courtesy of Valentino. According to an in-depth article on how the gown was created over on Eco Age, preparations for the big night were started back in November 2011. 


"Entering the Valentino Palace where the couture pieces are still designed, cut, sown and created by an expert team of seamstresses who had been there for many years," she writes. "The rooms here are filled with skillful women wearing white aprons, sometimes donning gloves so as not to mark the delicate fabrics and exquisite embroideries that they still do by hand. This is a painstaking operation where it takes many weeks to make a single gown."


Firth goes on to reveal that the dress is composed of fabric made from recycled plastic bottles and silk, saying that the end result "is the picture of elegance that I've always dreamed of since I was about ten." Adding that it's "the ultimate Cinderella dress and I think a triumph of ethics and Valentino's showstopping aesthetics."


Other participants last night included actors Kenneth Branagh and Demian Bichir in sustainable tuxes from Ermenegildo Zegna and Colin Firth, who chose to "reuse" his Tom Ford tux from last year's Academy Awards. 


Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

Green fashion hits Oscars red carpet
Livia Firth brings her Green Carpet Challenge to Hollywood's biggest event — with one giant surprise participant.