Hamburg Stromatolites in Hamburg, New Jersey

On a side street in this quiet community rests an unusual sight: an approximately 500 million-year-old rock outcropping covered in fossilized stromatolites. These are the remnants of colonies of cyanobacteria that once grew in thick mats on the shallow seafloor, adding layer after layer of accumulated sediment like the rings of a tree. The mats are preserved in the beautiful swirls and circles that dot the rock, an example of what’s called Allentown dolomite.

Stromatolites are still around today, but quite rare, with only a few living colonies, like the one in Shark Bay, Australia.