From Scientific American:
The oldest civilization of ancient Mexico and Central America has finally yielded solid evidence of a writing system. Researchers who analyzed a stone block covered in a sequence of faint symbols have declared it the oldest conclusive writing sample from the New World, dating to around 900 B.C. or earlier and belonging to the region’s oldest complex society, the Olmec. “Imagine if you will this extraordinary civilization that we’ve known about for 100 years suddenly to become literate. It gives them a voice in a way that’s not directly accessible through artifacts alone,” says one of the analysts, anthropologist Stephen Houston of Brigham Young University. He and his colleagues report their conclusions in the September 15 Science.
The Olmec, who are famous for having carved heads up to eight feet tall out of rock, held sway in so-called Mesoamerica (central Mexico to Costa Rica) from 1400 to 400 B.C. They constituted a major civilization, having several large cities and outposts as well as irrigation, iconography and a calendar. Signs of writing were strangely lacking, however, except for some controversial claims based on limited imagery.
More here.