Traces of the ancient timber structure was found under a brick temple that is itself within Buddhism's sacred Maya Devi Temple at Lumbini, in southern Nepal near the Indian border.
In design it resembled the Asokan temple erected on top of it. Significantly, it featured an open area, unprotected from the elements, from which it appeared a tree once grew.
"This sheds light on a very very long debate" over when the Buddha was born and, in turn, when the faith that grew out of his teachings took root, said archaeologist Robin Coningham in a conference call.
But much of what is known about his life and times has its origins in oral tradition, with little scientific evidence to sort out fact from myth.
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Many scholars have maintained that the Buddha -- who renounced material wealth to embrace a life of enlightment -- lived and taught in the 4th century BC and died in his 80s.
"What our work has demonstrated is that we have this shrine (at Buddha's birthplace) established in the 6th century BC" that supports the hypothesis that the Buddha might have lived in that earlier era, Coningham said.
Geoarcheological research meanwhile confirmed the existence of tree roots within the temple's central open area.
Coningham was co-director of an international team of archeologists at Lubini, partly funded by the Washington-based National Geographic Society.
Its peer-reviewed findings appear in the December issue of the journal Antiquity.
Lumbini today is a UNESCO world heritage site, visited by millions of pilgrims every year.