English — along with a whole host of languages spoken in Europe, India, and the Middle East — can be traced back to an ancient language that scholars call Proto Indo-European. Now, for all intents and purposes, Proto Indo-European is an imaginary language. Sort of. It's not like Klingon or anything. It is reasonable to believe it once existed. But nobody every wrote it down so we don't know exactly what "it" really was. Instead, what we know is that there are hundreds of languages that share similarities in syntax and vocabulary, suggesting that they all evolved from a common ancestor.
Of course, that very quickly leads to attempts to reconstruct what said ancestral language might have sounded like. In the track above, you can listen to University of Kentucky linguist Andrew Byrd recite a fable in reconstructed Proto Indo-European. Archaeology magazine helpfully provides a translation:
A sheep that had no wool saw horses, one of them pulling a heavy wagon, one carrying a big load, and one carrying a man quickly. The sheep said to the horses: "My heart pains me, seeing a man driving horses." The horses said: "Listen, sheep, our hearts pain us when we see this: a man, the master, makes the wool of the sheep into a warm garment for himself. And the sheep has no wool." Having heard this, the sheep fled into the plain.
Obvious, right? So how does one produce a scholarly mashup of English, Hindi, Urdu, and more, while accounting for six millennia of invention, sharing, and remixing?
There are a couple of different techniques. In the comparative method, researchers take two or more languages and start lining up their features side by side. What sounds do they share? What words sound similar? What rules do they have in common? Then you use what you know about the history of those languages to look at which ones descended from others, and to weed out words that were borrowed completely from unrelated languages thanks to trade or travel. Following the lines of descent, you can get an idea of the sounds and alphabets that the parent language originally had to work with.
The other technique, internal reconstruction, basically takes a single language and starts trying to work it backwards in time through itself. How did English distinguish itself from older Germanic languages and how has it changed since AD 500.
When you put information that you gather from both these techniques together, you can start to get a handle on what some really ancient, never-heard-by-anyone-living languages might have sounded like.
For instance, Wikipedia has a chart showing two different versions of the Proto Indo-European numbers. If you speak one of the languages descended from Proto Indo-European, these will likely look or sound familiar.