The present participle form: the ongoing process of becoming a fossil or becoming unchanging.
From fossilize + -ing (Old English gerund/present participle marker). The -ing form indicates continuous or ongoing action.
Right now, somewhere in the world, a creature is fossilizing—perhaps a woolly mammoth in Siberian permafrost or trilobites on an ocean floor—in conditions so perfect that our descendants will find it millions of years from now!
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