The Talmud, in Sanhedrin 56a-b, gives the Noahide laws, applicable to all mankind:
Our Rabbis taught: Seven precepts were the sons of Noah commanded: To establish courts of justice; and refrain from blasphemy, idolatry, adultery, murder, stealing, and eating the flesh of live animals.
It then explains that these laws are derived from a single line in Genesis:
And the Lord God commanded the man saying, ‘of every tree of the garden you may freely eat’. [Gen. 2:16]
Here is how:
-“Establish courts of justice” is derived from “And the Lord God commanded”, because “command” relates to justice and judgment.
-“No blasphemy” is derived from the words “The Lord”, which are used in connection with blasphemy in Leviticus: "And he who blasphemes the name of the Lord, he shall surely be put to death." [Lev. 24:16]
-“No idolatry” is derived from the word “God”, because the word “God” is used in that context in Exodus: "You shall have no other gods before Me. "[Ex. 20:3]
-“No murder” is derived from “the man”, because the word “man” is used in that context in Genesis: "Whoever sheds man's blood, by man shall his blood be shed." [Gen. 9:6]
-“No adultery” is derived from the word “saying”, because it used in that context in Jeremiah: "They say, ‘If a man puts away his wife, and she go from him, and became another man's…’"[Jer. 3:1]
-“No stealing” is derived from “Of every tree of the garden you may freely eat”. Since it was necessary to authorize Adam to eat of the trees of the garden, it follows that without such authorization it was forbidden, since the trees did not belong to him.
-“No eating flesh from live animals” is derived from “You may freely eat”, because it implies “You may eat only what is ready for eating, which is not the case while the animal is alive.”
Is this the ONLY source for the Noahide laws?
I ask because, considering their universality and their importance, it is puzzling that they have to be derived in such a contrived manner, instead of being spelled out directly in the Torah.