Geologists have found evidence that sea ice extended to the equator 716.5 million years ago, bringing new precision to a “snowball Earth” event long suspected to have taken place around that time.Led by scientists at Harvard University, the team reports on its work in the journal Science. The new findings — based on an analysis of ancient tropical rocks that are now found in remote northwestern Canada — bolster the theory that our planet has, at times in the past, been ice-covered at all latitudes.

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