Two distinct Gemaras grew from the one Mishnah, because the Mishnah was studied in two great centres at once. In the Galilee, the academies of Tiberias, Sepphoris and Caesarea produced the Gemara of the Jerusalem Talmud, largely complete by the early fifth century CE, when Roman pressure on the patriarchate cut the work short. Its Aramaic is the western, Galilean dialect, its discussions are terse and often elliptical, and it covers the agricultural laws of the first order in depth, since those laws applied only in the Land of Israel.
In Babylonia, the academies of Sura and Pumbedita continued for another century and more, and their Gemara, the core of the Babylonian Talmud, is far longer and more polished. Traditional accounting places its shaping in the generation of Rav Ashi and Ravina around 500 CE, with modern scholarship assigning a substantial role to anonymous later editors, the stammaim, working into the sixth and seventh centuries. The Babylonian Gemara covers about thirty seven tractates, concentrating on the orders in force outside the Land of Israel. History decided between the two: the Babylonian academies stood at the centre of the medieval Jewish world, and their Gemara became the authoritative one, so that an unqualified reference to the Talmud means the Babylonian.