Cākṣuṣa–Vaivasvata Manvantara Transition, Deva-Gaṇa Taxonomy, and Loka-Triad Etymology
Bhūr–Antarikṣa–Dyu
अतो ऽयं प्रथमो लोको भूतत्वाद्भूर्द्वजैः स्मृतः / भूते ऽस्मिन्भवदित्युक्तं द्वितीयं ब्रह्मणा पुनः
ato 'yaṃ prathamo loko bhūtatvādbhūrdvajaiḥ smṛtaḥ / bhūte 'sminbhavadityuktaṃ dvitīyaṃ brahmaṇā punaḥ
Therefore this first world, by virtue of being bhūta, is remembered by the twice-born as “bhūḥ”. And within this very bhūta, Brahmā again spoke of the second as “bhavaḥ”.