I'm just intrigued with this phrase. I did a teensy bit of research about it, and, as I thought, it is part of an ancient script... some other wording or translation of this is probably found in many of the world's religious, pagan, philosophical, and other texts. "Ashes to ashes..." you get the idea.
I came across a website that discusses the phrase in terms of scientific discovery and physics.
"When modern science extended the reach of its observation to the galaxies above and the microbes below, it made a surprising discovery: an atom proved strikingly similar to a solar system. Both were comprised of particles kept in orbit by the gravity of an energetic core. Modern technology had reiterated the wisdom of the ancients, who coined the very same discovery in the adage: As Above so Below."
Apparently, something called the Emerald Tablet of Hermes Trismegistus is a short work which contains this phrase.
From a Hermetic Fellowship site (http://www.hermeticfellowship.org/HFHermeticism.html), the question, "What is Hermeticism?" is answered. Hermeticism is a religious and philosophical/esoteric tradition based primarily upon writings attributed to Hermes Trismegistus.
Here is yet another link that explains the phrase to some degree:
If you're interested... check out the above links.