system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do humans know that we've only discovered a fraction of the species on Earth? And how is that possible given we're 8 billion strong?
gpt
There's an awful lot of species that are too small to really see, or live at the bottom of the ocean (which is a huge percentage of the surface of the Earth).   We've documented the surface pretty well for things big enough to hold in our hand or larger (and even of those, new species pop up quite often), but when you get to figuring out microscopic mites that live on things deep in the jungle, and worms that live in mud three miles below the surface of the ocean, we're probably a long ways away from finding all examples.