1st generation of eating kosher

When did Gd start to differentiate between pure and impure animals; which is the premise of eating #kosher? Arguably during the generation of #Noah, just read below:

Reading in #Genesis 7:2 the command that "of every clean beast you shall take seven, man and wife," the Gemara asked whether beasts have marital relationships. Rabbi Samuel bar Nahman said in Rabbi Jonathan's name that the command means of those animals with which no sin had been committed (that is, animals that had not mated with other species). The #Gemara asked how Noah would know. Rav Hisda taught that Noah led them past the Ark, and those that the Ark accepted had certainly not been the object of sin, while those that the Ark rejected had certainly been the object of sin. And Rabbi #Abbahu taught that Noah took only those animals (fulfilling that condition) that came of their own accord. Similarly, Rav Hisda asked how Noah knew (before the giving of Leviticus 11) which animals were clean and which were unclean. Rav Hisda explained that Noah led them past the Ark, and those that the Ark accepted (in multiples of seven) were certainly clean, and those that the Ark rejected were certainly unclean. Rabbi Abbahu cited Genesis 7:16, "And they that went in, went in male and female," to show that they went in of their own accord (in their respective pairs, seven of the clean and two of the unclean).