But Prasnopanishad(6000 BC) described the force that pulls objects down and keeps us grounded on earth without floating(Sage/philosopher Kanad -2nd century BCE, from school of Vaisheshika wrote commentaries based on vedas and upanishads)
In Prashnopanishad c...hapter 3 while describing the panchapranas, the apana vayu is said to be residing in the anus and genitals – paayoopasthepaanam.
It is responsible for throwing out from the body faeces, urine, semen, menstrual blood and foetus. Further, the upanishad says :
prithivyaam yaa devataa saisha purushasya apaanamavashatabhyaantaraa
"The devata that is in earth she supports this apana. She helps apana for throwing out from the body. "
Usually Space travelers face difficulty in excretion due to absence of gravitational force there. The link between apana and the earth aiding it is quite clear in this upanishad."
Further in his commentary to this upanishad, Adi Shankara ( 8th century AD ) says
‘tathaa prithivyaam abhimaaninee yaa devataa prasiddhaa saishaa purushasya apaanavrithimavashtabhyaak
"This devata blesses by supporting apana by pulling in the downward direction. Or else, the body would have floated up."