Archaeologist Emilio Estrada and co-workers wrote that pottery which was associated with the Valdivia culture of coastal Ecuador and dated to 3000–1500 BCE exhibited similarities to pottery which was produced during the Jōmon period in Japan, arguing that contact between the two cultures might explain the similarities. Chronological and other problems have led most archaeologists to dismiss this idea as implausible. The suggestion has been made that the resemblances (which are not complete) are simply due to the limited number of designs possible when incising clay.