[Razengan]

We already know what can last for literally millions of years: Life.

Maybe we could encode some information in birdsong, tree rings, or the matting patterns drawn by fish in the seafloor. :)

https://www.youtube.com/watch?v=hpdlQae5wP8

[shantara]

This reminds me of Whisper, one of my favorite exotic alien concepts. The alien civilization in question has selected a planet with as stable environment as possible, and planted it full of genetically engineered grass. The sound of wind blowing through the grass creates an acoustic computer which hosts a virtual space its creators have uploaded themselves into.

https://www.orionsarm.com/eg-article/470007b39d192

[Razengan]

I have never heard anything like that (using sound) before. Amazing!

[philipswood]

A SF short story about a biologically encoded message from ancient aliens (written by one of the Autodesk founders): We'll Return, After This Message by John Walker

https://www.fourmilab.ch/documents/sftriple/gpic.

[vmilner]

It's fascinating that in 1983 it was thought that a 768-bit RSA number would take 40 million years to factor. (It actually took 26 - RSA-768 was factored in 2009.)

[ars]

The link seems broken? Should be: https://www.fourmilab.ch/documents/sftriple/gpic.html

[istjohn]

Or directly encode the message in DNA itself. I suppose the difficulty would be devising an encoding with enough redundancy or other features to preserve the information content over many generations of evolutionary pressures.