Preserving a DVD with Liquid Nitrogen

Here's the game: you have a message that's about 1 Gigabyte long, and you want to preserve it for as long as possible. Not just a few years, or even a few decades or centuries, but for thousands to millions of years!

It's a cool engineering question because you can explore what happens if society collapses for a time, or if the climate changes dramatically.

Some good ideas I've heard so far have been:

• Write the message in the DNA of a bacteria and set it loose in the world. (But in as much as all that information is not adaptive, the bacteria will evolve to remove it from its genome!)
• Write the message carved into gold/platinum/iridium and bury it deep. It will never degrade and hopefully be unnoticed for a long time. (But if its made of economically valuable material it might end up like the gold capstone of the pyramids of Egypt – scavenged and melt down!)
• Write the message on a metal plate and launch it into earth orbit. Prof. Sussman thought of this idea, and I think that it's one of the best ones so far! Up in space, it's vanishingly unlikely that the message would be disturbed for something like millions of years!
• Keep the information in a computer, and keep copying it to new media long before the old media starts to degrade. This is how important data is currently preserved. It's a beautiful form of immortality that gets it's power by recognizing that while the material substrate of a signal may change, the signal can remain constant.

I was surprised to learn that modern DVDs won't really last for much more than around 50 years, because the dyes and plastic they're made of slowly chemically degrade over time. However, if you put a DVD in liquid nitrogen, the extreme cold stretches that 50+ years into trillions upon trillions of years! I was curious as to whether I could cool down a DVD to liquid nitrogen temperature, warm it up, and then read the data again.

So, here are a few scripts to help in the experiment:

One to create a DVD image, which is around 3.5GB.

#!/bin/sh
mkisofs -iso-level 4 -r -o ./test-image.iso \
        -graft-points test-files=test-files

One to burn the image to the DVD.

#!/bin/sh
growisofs -dvd-compat -Z /dev/cdrom=./test-image.iso

And another to compare the DVD to the image files.

#!/bin/sh
mkdir -pv cd-mount
sudo mount /dev/sr0 cd-mount
diff -sr test-files cd-mount/test-files
sudo umount cd-mount
rmdir cd-mount

And without further ado, the experiment!

Contained within the boiling liquid nitrogen, all chemical reactions cease. The only things that interact with the DVD are light (put it in a dark container), cosmic rays (which don't damage the relatively large data storage components of the DVD), and the kinetics of the liquid nitrogen itself (embed the DVD in a solid container and don't let it touch the LN).

If only it was for people as it is for DVDs…