Words, grammatical forms and meanings linked to the ontology.
bya en · SYM
Meanings
(usually) Abbreviation of billion years ago (A symbol for a unit of measure.) ▸ Synonym of Gya (“billion years ago (short scale): 10⁹ years ago”).
The first (oldest) unit of time is the Precambrian Supereon, which covers much of Earth's history from its origins roughly 4.55 bya to 545 mya. Very primitive, one-celled life-forms arose as early as 4.0 bya and near the end of the era (570 mya) the oldest known fossils of multi-celled organisms appear. 2015, Joyce A. Quinn, Susan L. Woodward, “Introduction”, in Earth's Landscape: An Encyclopedia of the World's Geographic Features, volumes I: A–L, Santa Barbara, CA: ABC-CLIO, →ISBN, page xxxi:
(dated, uncommon) Abbreviation of billion years ago (A symbol for a unit of measure.) ▸ billion years ago (long scale):10¹² years ago: a trillion years ago (short scale).