What's the oldest living thing you've ever seen? A 2,200-year-old sequoia in California, perhaps? That's a relatively teenage specimen to the artist Rachel Sussman, who has spent the last ten years looping the globe on a wild adventure to meet and document the world's oldest "continuously living" organisms.

I remember looking toward the edge of town and thinking that something seemed off. We had stopped here before crossing the Continental Divide, in one of those typically charming Colorado mountain communities. Yet a few blocks away from its railroad-era Main Street lined with historic 1890s structures, there were…