system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If fusion reactors fuse hydrogen into helium, wouldn't we run out of hydrogen at some point?
gpt
Hydrogen is the most abundant substance in the universe. 90% of all the atoms that exist are hydrogen. There is so much hydrogen locked up in fossil fuels that we could just use them for millennia before we even started using water, or sending spaceships to collect it.