The fragment is believed to have come from Egypt and contains writing in the Coptic language that says, "Jesus said to them, 'My wife...'" Another part reads: "She will be able to be my disciple."
Its discovery in 2012 caused a stir. Since Christian tradition has long held that Jesus was not married, it renewed long-running debates over celibacy and the role of women in the church.
The Vatican's newspaper declared it a fake, along with other scholars who doubted its authenticity based on its poor grammar, blurred text and uncertain origin.
But a new scientific analysis of the papyrus and the ink, as well as the handwriting and grammar, show that the document is ancient.
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"No evidence of modern fabrication ("forgery") was found," the Harvard Divinity School said in a statement.
The palm-sized fragment likely dates to between the sixth and ninth centuries, and could have been written as early as the second century CE (common era), said the study results published in the Harvard Theological Review.
Radiocarbon dating of the papyrus and a study of the ink using Micro-Raman spectroscopy was done by experts at Columbia University, Harvard University and the Massachusetts Institute of Technology.
"Current testing thus supports the conclusion that the papyrus and ink of GJW are ancient."
The origin of the papyrus is unknown. Karen King, a historian at Harvard Divinity School, received it from a collector -- who asked to remain anonymous -- in 2012.
King, a historian of early Christianity, said the science showing the papyrus is ancient does not prove that Jesus was married.