Astronomy- Gravity of earth

तथा प्रिथिव्यामाभिमानिनी या देवता प्रसिद्दा सैषा 

पुरुशस्य अपानावृत्तिमावास्ताभ्याक्रुष्य: वाशिकृत्याध एव 

अपकर्शेना अनुग्रहं कुर्वती वर्तत इत्यर्थः | अन्यथा 

हि शरीरं गुरुत्वत पतेत सावाकशे वोद्गाछेत ||

Tatha prithivyaamabhimaanani ya devata prasidda saisaa

purusasya apaanavrittimavastabhyakrusha vasikrutyadha eva

apakaesenaanugraham kurvati vartat ityarthaha | anyatha

hi shariram gurutvat patet saavakaase vodgacchet ||

"Similarly the deity that is earth exists by favouring, attracting, controlling by pulling down the vital function called Apana of the human. Else the body would fall due to its weight or would fly into the sky if left free".

Source: Sankara's commentary (8th century A.D) on Prasnopanishad (vedic period), chapter 3, Mantra 8