A total of 15 ideas from around the world, including a “Great Bubble Barrier” to catch plastics before they reach the ocean and a zero-waste city, are in the running this year.
Five winners will be announced in the US next month, with each receiving £1 million ($1.1m) to develop their projects.
44.01, based in Oman, mineralises carbon dioxide in peridotite in an accelerated process which also occurs in nature. The company is named after the molecular mass of CO2, and was selected from a pool of more than 1,000 applicants.
Two British-based entries have made the shortlist, making it the first time UK projects have made it to the finals.
Notpla Hard Material, a London start-up run by Pierre Paslier and Rodrigo Garcia Gonzalez, makes packaging from seaweed and plants as an alternative to single-use plastic.
It has already created more than one million biodegradable takeaway food boxes for the company Just Eat.
The other UK finalist — Low Carbon Materials (LCM) based in County Durham, UK, — uses unrecyclable plastic waste to make traditional concrete blocks carbon zero.
“Until now, construction has been one of the hardest industries to decarbonise,” said Natasha Boulding, a co-founder of LCM.
“With LCM, that could all change. We’ve turned concrete net-zero and now we need the world to start using it.”
Earthshot awards — in pictures
The Prince of Wales described the finalists as “innovators, leaders and visionaries” and said they proved there are “many reasons to be optimistic about the future of our planet”.
“They are directing their time, energy and talent towards bold solutions with the power to not only solve our planet’s greatest environmental challenges, but to create healthier, more prosperous and more sustainable communities for generations to come,” he added.
Prince William took inspiration in launching his ambitious 10-year £50m prize competition — which is designed to find solutions to repair and regenerate the Earth — from former US president John F Kennedy’s Moonshot project.
The prince said he was “so excited” to celebrate the finalists and meet the winners when he and the Princess of Wales head to Boston — Kennedy’s home town — on December 2 for the awards gala.
Among the other finalists are The Great Bubble Barrier, from the Netherlands, which uses air pumped through a perforated, underwater tube to create a curtain of bubbles that directs plastic up to the surface and into a waste collection system.
The City of Amsterdam Circular Economy is also a potential winner, with its citywide initiative to establish a fully circular economy by 2050, wasting nothing and recycling everything.
Prince William gives Earthshot speech in Dubai — video
Mukuru Clean Stoves from Kenya provides cleaner-burning stoves to reduce unhealthy indoor pollution and provide a safer way to cook.
The initiative was started by Charlot Magayi, who grew up in one of Nairobi’s largest slums, Mukuru, and who used to sell charcoal for fuel.
Ms Magayi suffered from repeated respiratory infections due to pollution and then sought an alternative solution after her daughter was severely burnt by a charcoal stove in 2012.
Her eco-stoves use processed biomass made from charcoal, wood and sugar cane and cause 90 per cent less pollution than an open fire, and she plans to create an even cleaner version that burns ethanol.
Others in the finals include Fleather — a leather made out of floral waste in India; Oman-based 44.01, which eliminates CO2 by mineralising it in rock; Hutan in Malaysia — a conservation organisation that creates wildlife corridors to give orangutans safe passage to new habitats; and the Indigenous Women of the Great Barrier Reef group from Australia, who use ancient knowledge and digital technologies to protect the land and sea.
There are five Earthshot categories: Protect and restore nature; Clean our air, Revive our oceans; Build a waste-free world; and Fix our climate.