What is considered the earliest documented form of writing?
The earliest extant form is the cuneiform (wedge-shaped) writing on clay tablets from the Mesopotamian Sumerians at the end of the 4th Millennium, B.C.E. There is speculation that there may have been a predecessor form of “writing” but the theories are contradictory and unclear.
The first forms of writing were mainly for accounting and shipping manifests. Originally the Mesopotamians sent little clay shapes sealed inside of jars along with their trading caravans as a record. Once the caravan of livestock arrived the buyer would break open the jar and check to make sure the number of cattle matched the number of ‘cattle’ shapes. Over time sellers realized that it was easier to press the shapes into wet clay and send the hardened impressions along as an inventory.
I would gander that the first forms of writing were numbers and names. It was a while before people devised phonetics.
However, this article:
http://news.bbc.co.uk/1/hi/sci/tech/235724.stm
Speculates that the Egyptians may have actually invented it, and their contemporaries, the Sumerians copied glyphs for their writing. This is still in dispute and my book on writing systems says that cuneiform is probably (but not definitely) the first. Fact remains, that the writing in that area began as a way of record keeping.
However, not all writing started as record keeping. The earliest Chinese writings (oracle bone inscriptions) were for divination purposes. Chinese writing developed independantly of other cultural influences. The earliest records of any Chinese writing begins at about the second half of the second millenium BCE.
And actually Cuneiform is simply a “simplification” of earlier pictograms which were inscribed, it was later that wedge shaped styli were used to create what we know as cuneiform.
In this thread, I asked What is the oldest written document?.
It appears that the oldest legible document is an Egyptian tablet that read “mountain of light”. You can find a picture here, along with an article about early writing.
The oldest written document is probably this Harappa tablet dating to about 3500 bce, found in Pakistan.