This begins with I think, therefore I am, the translation of Descartes’ Je pense donc je suis (1637) or the more common cogito ergo sum (1644).
The Google Ngram Viewer reveals “I think therefore I am” taking off in (non-periodical) print around 1900.
The snowcloneification was surely not far behind, since so many people would already have been familiar enough with this cliche of philosophy. Something else will very occasionally occur in place of “am” (“I knit, therefore I blog“), but this generally weakens the tie to the original–unless the composer of the snowclone is very clever.
X is often single-syllable verbs, no doubt to help evoke the original, but longer words are possible: smell, skate, rez, tweet, drink*, fink*, shrink*, consume.
* Note the rhyming with the original think.
The Snowclones Database 