The ancient Olmec civilization probably produced the faintly etched symbols around 900 B.C., or roughly three centuries before what previously had been proposed as the earliest examples of writing in the Americas.
"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 pattern of symbols covering the face of the rectangular block also represents a previously unknown ancient writing system.
The text contains 28 distinct glyphs or symbols, some of which are repeated three and four times. The writing system does not appear to be linked to any known later scripts and may represent a dead end, according to the study.
Other experts not involved in the study agreed with Houston and his colleagues that the horizontally arranged inscription shows patterns that are the hallmarks of true writing, including syntax and language-specific word order.
"That's full-blown, legitimate text — written symbols taking the place of spoken words," said William Saturno, a University of New Hampshire anthropologist and expert in Mesoamerican writing.
The text is roughly arranged in rows across the block's face, which mirrors almost exactly the dimensions of a standard legal pad. At 5 inches thick and 26 pounds, the tablet is far more hefty, but still portable.
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.
There is little hope of deciphering the meaning of the text. The small size of the block and the faintness of the inscription imply the text was not a public document, but instead was meant for intimate reading, Houston said. Some suggested it may have had a ritual use.
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 this year to examine and photograph the block.
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 find bolsters the early importance of the Olmecs, who flourished between about 1200 B.C. and 400 B.C., before other great Central American civilizations such as the Maya and Aztec. They are best known for the massive heads they carved from stone. The village where the block was found is close to a site called San Lorenzo, believed to be the center of Olmec civilization.
"To me, this find really does bring us back to this idea that at least writing and a lot of the things we associate with Mesoamerican culture really did have their origin in this region," Stuart said.