In 1965, a diver looking for sponges off the coast of Cyprus discovered the remains of a ship at the bottom of the Mediterranean Sea. When archaeologists pulled the Greek Hellenistic-period vessel to the surface, they realized it was transporting a cargo of wine and almonds.

Now, six decades later, those almonds have helped researchers piece together the shipwreck’s timeline. An analysis of the nutritious nuts, along with samples of wood taken from the ship’s timbers, suggest it sank between 286 and 272 B.C.E., according to a study published last week in the journal PLOS One.

Researchers have been studying the 46-foot Kyrenia shipwreck for years. They know it had a crew of four, was constructed from wood with lead sheathing and had one mast with a square sail.

“A shipwreck’s contents can tell us specifically which items were being traded or exchanged, where and how people were moving around by sea, which groups of people were in contact with one another and how they were impacted by these early social and economic networks,” says study co-author Brita Lorentzen, an anthropologist at the University of Georgia, to Reuters’ Will Dunham.

But while researchers were able to glean a lot of information from the wreck, its age remained a mystery.

They had previously attempted to date the ship by analyzing some of the items found onboard, including coins and pottery. These analyses suggested the ship sank sometime during the late 300s B.C.E., according to a statement from the researchers. Later, they estimated the ship actually sank between 294 and 290 B.C.E., but they still weren’t certain.

Researchers wanted more conclusive evidence, so they turned to radiocarbon dating and dendrochronology, a dating technique that involves studying tree rings.

But first, they had to overcome a major hurdle. When the shipwreck was pulled from the water in the 1960s, conservators applied a petroleum-based compound called polyethylene glycol (PEG) to the wood to slow its decomposition.

“Adding PEG prevents ship timbers from drying out, shrinking and turning to dust out of the water,” Lorentzen tells Reuters. “But it also contains petroleum, with lots of carbon from long-ᴅᴇᴀᴅ organic remains.” As such, any samples treated with PEG would skew the results of radiocarbon dating studies.

The researchers developed a novel method for removing PEG from wood, which they tested on samples of wood from the Roman era that had already been dated using dendrochronology, per Popular Science’s Laura Baisas. Their technique worked, so they attempted it on a sample from the Kyrenia wreck; they also tracked down an untreated piece of timber from the wreck that had been sitting in a museum.

Their analysis suggests the ship’s timbers came from trees that grew in the later part of the fourth century B.C.E. The trees were likely cut down after approximately 355 to 291 B.C.E.

They also studied some of the fresh green almonds that went down with the ship, as well as a piece of bone from either a sheep or a goat. Using statistical modeling, they were able to determine that the ship probably sank between 286 and 272 B.C.E.

Along the way, they also found and corrected a discrepancy in the scientific standard researchers use when analyzing old wood, so their paper has broader implications for the study of other ancient shipwrecks.

Why were the researchers able to succeed in dating the ship when others had failed? “The [radiocarbon] dating and dendrochronology fields have grown, developed, refined their results over many decades,” says Mark Lawall, a classicist at the University of Manitoba in Canada who was not involved with the research, to CNN’s Taylor Nicioli.

“Science—whether hard or soft—develops over time through a lot of work in the trenches,” he adds. “It takes time, and it needs time.”