One reason Earth is not entirely a closed
system is because

The Earth is a closed system for matter

That is a list of all basic elemental materials on our planet. Because of gravity, matter (comprising all solids, liquids and gases) does not leave the system.

a≈452.39cm²

explanation:

radiative zone

explanation    

radiative zone is the layer of the sun which energy is transferred away from the core by radiation. although, the core is the only part of the sun that produces an appreciable amount of heat through fusion. in fact, 99% of the energy produced by the sun takes place within 24% of the sun's radius.