We've discovered lots of Sumerian documents, but I understand that there is some debate as to chronology which means we aren't sure what year, exactly, any of them were written. What is the earliest document where the year of writing can be determined with certainty?
For bonus points, what is the earliest document where we can tell the exact day it was written?
The documents that are best suited for accurate dating are astronomical texts. The precise dates of historical eclipses or comets can be calculated using current data and correlated with observations made in ancient texts. The chronology of Assyria, as an example, is partially based on observations of eclipses by Assyrian astronomers. A solar eclipse mentioned in the Assyrian eponym canon occurred on 15 June 765 BC. (Source: [Cambridge Ancient History: Assyria] (http://books.google.com/books?id=XRY7AAAAIAAJ&pg=PA24)) That date has been used to determine the years that the Assyrian kings reigned.
There's a question about the oldest specific date we know, which would be based on documentary evidence, but the documents may be dated from later and uncertain.
The oldest document dated to a specific year I could find is an ostracon (a bit of pottery written on like scratch paper) which records the delivery of various goods and dates to 1246 BCE.
As a semi-related follow up question. What is the earliest document to have used the Christian year system and when was it?