The earliest artifact I can find that marks my presence on the Internet is 30 years old today. The fact that it is still there should tell you something about the longevity of your posts and tweets. (It may not have been my actual earliest post, just the oldest that has survived until today.)
Thanks to Google, we can see my post to the fa.editor-p newsgroup. "fa.editor-p" is descried as an "Interest group in computer editors, both text and program." The "fa" means "From ARPAnet" and the "p" stands for "people".
At 9:50 pm I was probably at home accessing the PDP-11/70 at Zehntel via a dumb terminal (not really as perjorative as it sounds) over a modem of somewhere between 300 and 1200 baud. Even my email address at the time looks like something out of a badly written movie: menlo70!sytek!zehntel!steve@Berkeley - some ungodly combination of UUCP mail gatewaying into ARPAnet.
For even more fun, go to http://olduse.net tonight after 9:50pm and nav your way into fa.editor-p you'll see my post in all its green phosphor on black screen glory. This project is described as "Olduse.net is Usenet, updated in real time as it was thirty years ago."
And I love this Q&A from its FAQ:
Q: What about privacy? I posted something 25 years ago that I regret.
A: It's not like this is the only copy of this archive of Usenet. Not a lot can be done about something that has by now echoed its way across the net for decades.
Think about that next time you tweet!