system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 - Why does Earth have a weak magnetic field and why is it weakening?
gpt
For Earth it's thought to be due to the molten outer core which is liquid metal.  The flow of this liquid metal generates an electric current and since the Earth rotates this generates an magnetic field (rotating electric fields create a magnetic field and vice versa).  


As to why it's weakening........ that we don't really understand.  It's thought that it's possibly due to inner workings of the liquid outer core that we don't really understand.  However, after it weakens it'll flip polarity and then strengthen again.

However, over time the outer core is solidifying and this will eventually most likely stop this but this will take a long time, like billions of years.