I am not sure if it is your RAM or your "HD memory" that is running out of space.
Most phones only have only 1Gb or 2Gb of RAM and when switched on that will already have the operating system in it, plus any apps you are running.
If Google Earth needs to download more map information from the internet then that will go in memory as well, so it could fill up your RAM memory.
Phones also have "HD memory" (solid state) which holds all the software, apps, personal files, music, videos etc. when the phone is switched off.
Some phones only have 8Gb or 16GB of memory, and often this can be half full up when you get the phone (holding the operating system, apps etc)
As you download more apps and more data this can also fill up.
Maybe Google Earth is downloading more map data and storing this in your "HD memory" (even temporarily) and that is then filling it up.
Check your "HD memory" and maybe clear out some space by either deleting files you no longer need (photos etc), or moving them to another device or into the cloud.