Old Testament Written in Aramaic?

Peter Watson, The German Genius, pg 66

Even by the end of the seventeenth century [.. there were criticisms directed towards religion]. The Bible also came under more systematic criticism when it was shown that the original Old Testament had been written not in Hebrew but in Aramaic, meaning the old scriptures could not have been dictated to Moses by God: the Old Testament was not “inspired”.

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Now that’s a big can of whoop-ass, isn’t it? The easiest way to verify this is to carbon date this so-called original OT I guess.