"It is" used as "there is": what is the origin?
Ok, this is a somewhat nonstandard English question. In the Southern US, or at least in Central Virginia, there is an idiomatic use of the phrase it is that is equivalent to the expression there is, as in
It is not enough gas in my tank to make the trip.
Not being from the South myself, I'm puzzled by this particular usage. I thought the proper (not to mention, less ambiguous) way to phrase the sentence above was
There is not enough gas in my tank to make the trip.
Compare these two sentences:
Is it anything for dinner?
Is there anything for dinner?
How did this expression originate?
The origin is somewhat surprising. It dates back to Old English, according to the OED's entry for it:
As the subject of an existential clause: = there adv. 4d. Now chiefly U.S. regional (south. and south Midland).
In Old English esp. with following that-clause; compare A. 4a(b).
The earliest example they give is this one, from "early Old English" (luckily I was able to find a translation):
Is hit lytel tweo ðæt ðæs wæterscipes welsprynge is on hefonrice; ðæt is Halig Gæst.
Gregory's Pastoral Care by King AlfredThere is little doubt that the well-spring of this wæterscipe is in heaven, that is the Holy Spirit.
A Handbook of Anglo-Saxon Studies
In addition, some examples from Middle English can be found here under 4b.(b).
From circa 1384 (?), written by John Wycliffe, an early translator of the Bible into English and a devout anti-papist reformer:
And ȝif men speken largili, many men ben here more blessid þan þe pope; for hyenes of þis state makiþ not bi himsilf man blessid, for ellis ech pope were blissed, al ȝif he were falsly chosen of fendis; and Scariod shulde be blissed, as he was chosen by Crist himself. And it is no nede to argue here for to disprove þis foli, for it is more fals in himsilf þan ouȝt þat men shulen bringe herof.
These writings appear in The Select English Works of John Wyclif, edited by Thomas Arnold, Volume 3, and published in London in 1871 (pp. 344-345).
[yogh (ȝ) approximates "y" or "ou" (as in ouȝt = ought); thorn (þ) approximates "th"; "hyenes" = highness; "foli" = folly, etc.]
Apart from Old English, the return of this style may be influenced by German native speakers who wrongly take German wording into English sentences, as all those sentences, when translated to German, use the word es (English: it); but in German, the usage of es is perfectly fine:
There is not enough gas in my tank to make the trip.
Es ist nicht genug Benzin in meinem Tank, um die Reise zu machen.
and
Is there anything for dinner?
Gibt es etwas zum Abendessen?