Simplify the following text for a Grade 14 native English-speaking person.
Original: In soil science , humus ( Origin : 1790 â `` 1800 ; ( Latin : earth , ground ) refers to any organic matter that has reached a point of stability , where it will break down no further and might , if conditions do not change , remain as it is for centuries , if not millennia .
Simplified: In the earth sciences , `` humus '' means any organic matter which has reached a point of stability , where it will break down no further and might , if conditions do not change , remain essentially as it is for centuries , or millennia .