When was Marriage first instituted?

What are the implications regarding lawful marriage versus riding in on a horse and grabbing some fair maiden from yonder village (like in the movies)?

The word for marriage does not show up until Lot (Genesis 19:14) ... and even there, the sense in Hebrew is carrying away some yon maiden. The context however is clear with the word "in-law" (masculine) for the men who married into that family. The Hebrew term is bridegroom, meaning a lawful wedding occured. The strong family connection seen in the context affirms this lawful union.

The use "in law" (feminine) occurs in Genesis 11:31 for Sarah ... where the Hebrew term for bride is used, meaning a lawful wedding occured. Sarah is treated as a full-up sister/daughter in her new family. This close family tie by means of a lawful wedding shows up ruefully later when Abraham claims Sarah is "only his sister" for which he is severely chastised for hiding the fact that she was his wife. He was telling the truth ... sort of.

Terah's family is the first reference for lawful marriage. However, in Genesis 7:7 Noah and his kids references the term wives and wife. This is the same term connected to Genesis 2:24-25 where God establishes the ordinance of exclusivity between husband and wife.

In Hebrew, the term wife comes across as "His specifically assigned woman". The term carries a meaning of 'lawfully' wedded, although there were no known governments establishing laws at that time.

"Loose women" would not have the term 'wife' applied to them. In tribal societies, even the most backward, the parents are deeply involved with the arrangements with their offspring's life-partner. The term wife carries with it a life-time commitment on the part of the husband, which from a Biblical standard is called "marriage".

This type of threological argument is similar to the rhetoric that "Trinity" does not appear in the Bible but the theological concept is clearly there. Likewise, even though "marriage" and "in law" is not used prior to Abraham (when governments existed), the concept goes clearly as far back as Adam.

I can say this boldly because Jesus quotes Genesis 2:24 as the case for marriage ... and, as Messiah, he obviously has the correct interpretation.