Identify the subsystem of earth that takes the longest amount of time to change, based on the geologic time scale

Geosphere  or lithosphere took the longest time to form

Explanation:

There are basically four subsystems of planet earth -

a) Geosphere  or lithosphere - consists of land mass and all rocky strata

b) Hydrosphere: - Water reserves on earth

c) Biosphere: living things on earth

d) Atmosphere: - Gases around the earth

Out of these four subsystems , the one that took the longest time for changing is Geosphere  or lithosphere

Some changes in this subsystem have happened  only in a short span of time i.e instantaneouly such as rotation of the Earth, earthquake  etc.

While some chnages have taken billion of years such as formation of coal and petroleum, formation of plate tectonics

what are the options