The earliest known punctuation is on the Mesha Stele http://en.wikipedia.org/wiki/Mesha_Stele and is a record of the Moabite king Meshas victories against the Kingdom of Israel

“The earliest writing had no punctuation, in fact, often had no space between words, until around the 9th century A.D. Some Roman monuments might have centred dots between words. The terms “comma,” “colon,” and “period” were invented by the librarian in Alexandria in the 3rd century B.C., but the marks corresponding to these terms were different from the marks we use today, and they were not generally accepted. Even when spacing between words was used, it was haphazard, rather like spelling before printing. The hyphen was introduced around the 11th century, to indicate that word was continued on the next line, but these word breaks were not at natural syllables as they are today.”

– extracted from Punctuation, http://www.nyu.edu/classes/copyXediting/Punctuation.html

Another source differs from the above, stating that punctuation was first introduced in the 5th century BC by Greek Dramatists such as the Euripides and Aristophanes. For more information, you might be interested in the following book:

Title: Cassell’s guide to punctuation

Author: Loreto Todd