...that caused the apparently contemporaneous development of agriculture on opposite sides of the world?

...fresh evidence, in the form of Peruvian squash seeds, indicates that farming in the New and Old Worlds was nearly concurrent. In a paper the journal Science published last June, Tom Dillehay, an anthropological archaeologist at Vanderbilt University, revealed that the squash seeds he found in the ruins of what may have been ancient storage bins on the lower western slopes of the Andes in northern Peru are almost 10,000 years old. “I don’t want to play the early button game,” he said, “but the temporal gap between the Old and New World, in terms of a first pulse toward civilization, is beginning to close.”

Let's see if they find a monolith.