Washington ? It’s more than idle doodling and the meaning is unclear. But there’s one thing researchers are sure of: The insect, ear of corn, inverted fish and other symbols inscribed on an ancient stone slab are the earliest known writing in the Western Hemisphere.

The arrangement and pattern of the symbols suggest the ancient Olmec civilization was using written language roughly three centuries earlier than previously proposed.

“We are dealing with the first clear evidence of writing in the New World,” said Stephen Houston, a Brown University anthropologist. Houston and his U.S. and Mexican colleagues detail the tablet’s discovery and analysis in a study appearing this week in the journal Science.

The patterns covering the face of the rectangular block also represent a previously unknown ancient writing system – a rare find in archaeology.

The text covers the block’s face, which is almost exactly the dimensions of a standard legal pad. However, at 5 inches thick and tipping the scales at 26 pounds, the tablet is decidedly more hefty.

The face is smooth and slightly concave, which suggests it may have been worn down in antiquity as it was inscribed and erased multiple times, Houston said.

Villagers in the Mexican state of Veracruz discovered the tablet sometime before 1999, while quarrying an ancient Olmec mound for road-building material. News of the discovery slowly trickled out, and the study’s authors traveled to the site earlier this year to examine and photograph the block.

These images provided by the journal Science show the Cascajal block found in Veracruz, Mexico, at left, and a drawing of the symbols on the block. The stone block inscribed with patterned images found in Veracruz is believed to be the oldest example of writing in the New World.

Based on other materials, including pottery shards, believed found with the slab, the team concluded it is roughly 2,900 years old. Isolated signs similar to those inscribed on the block also appear on even older figurines found elsewhere in Mexico.

In 2002, other experts claimed an Olmec cylindrical seal and chips from a stone plaque contained the oldest examples of writing in the Americas. Some have disputed their interpretation of those symbols, which date to roughly 650 B.C.

“This is centuries before anything we’ve had. People have debated whether the Olmecs had any writing. This clears it up. This nails it for me,” David Stuart, a University of Texas at Austin expert in Mesoamerican writing, said of the new find. Stuart was not connected with the discovery but reviewed the study for Science.

The block contains 28 distinct glyphs or symbols, some of which are repeated three and four times. The writing system doesn’t appear to be linked to any known later scripts and may represent a dead end, according to the study.