FWIW, only last week I heard an interview with an ancient language scholar (Dr. Michael Heiser) say that he knows of no serious linguist who takes the gap theory seriously because it’s not supported by the Hebrew. I am unsure what program I was listening to now, but I found a blog post on his website on the topic.
Genesis 1:2 and the “Gap Theory”
http://drmsh.com/2010/09/28/genesis-12-and-the-gap-theory/
Dunno, but I think “How long was the earth around before Gen 1:2?” is a good question.