The high seas, the vast waters beyond any one country’s jurisdiction, cover nearly half the planet. On Friday, a hard-fought global treaty to protect the “cornucopia of biodiversity” living there cleared a final hurdle and will become international law.

The High Seas Treaty, as it is known, was ratified by a 60th nation, Morocco, crossing the threshold for United Nations treaties to go into effect. Two decades in the making, it allows for the establishment of enormous conservation zones in international waters.

Environmentalists hailed it as a historic moment. The treaty “is a conservation opportunity that happens once in a generation, if that,” said Lisa Speer, who directs the International Oceans Program at the Natural Resources Defense Council.

It is also a bright spot amid a general

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