From stones to dinosaur bones, treasures from deep in the earth will fill Union Chapel Saturday and Sunday for the Vineyard’s 15th annual National Fossil Day celebration.

The free, all-ages event will be an opportunity to check out geological specimens and meet experts from Harvard, Yale and the American Museum of Natural History.

Fossil Day was started by the National Parks Service in 2010, and celebrations happen all over the country. The first Fossil Day on the Vineyard was spearheaded by “Fossil Fred” Hotchkiss, a retired scientist who lives in Vineyard Haven.

Now in its 15th year, the Island’s celebration has grown significantly, thanks in part to a nonprofit collective of local geology enthusiasts called the Martha’s Vineyard Geological Society. Bart Jarek, a member of the Geological Society and organizer of Fossil Day, has enjoyed being a part of the event’s transformation.

“I’m happy to see everyone return,” he said.

Inside Union Chapel, experts and enthusiasts will display tables of specimens and information for guests to browse, giving people a chance to engage in hands-on learning and conversation. Mr. Jarek said that anyone is welcome to bring specimens along for identification, but that the only necessary thing to bring is curiosity.

“You can just come in empty-handed and open-minded and walk around and look at the tables, maybe even pick up fossils and talk about them with presenters,” he said. “The goal [is] public education, public inspiration and public enlightenment.”

For Mr. Jarek, Fossil Day is a chance to help people dig up enthusiasm for the natural world. In an increasingly digital environment, he hopes Fossil Day can help people slow down and appreciate the present by looking at the past.

“We’re people, we’re mammals, we come from a physical environment,” he said. “We’re losing touch with that, and we have the evidence of incredible timescapes and different periods of evolution and ecosystems right under our feet.”

National Fossil Day celebration takes place on Oct. 18 and 19 from 1 to 4 p.m. at Union Chapel in Oak Bluffs.