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The sulfate deposit, made mainly of jarosite, a hydrous sulfate, was interpreted to have formed when the blanket of volcanic pyroclastic materials came to rest on a glacier and reacted chemically with the ice.

A yellow-brown mineral called jarosite—rare on Earth but abundant on Mars—has been identified deep in an Antarctic ice core.

The discovery made headlines, because jarosite needs water to form, along with iron, sulfate, potassium, and acidic conditions.

Another idea was that the jarosite was born within massive ice deposits that might have blanketed the planet billions of years ago.

As ice sheets grew over time, dust would have accumulated within the ice—and may have been transformed into jarosite within slushy pockets between ice crystals.