Earth is approximately how old?
Geological time scale divides Earth's 4.5 billion year history into eons, eras, periods and epochs based on stratigraphy and fossil succession. Precambrian accounts for 87% encompassing Hadean, Archean and Proterozoic eons before Phanerozoic with Paleozoic, Mesozoic and Cenozoic eras. Major events include first life 3.5 billion years ago, Cambrian explosion, breakup of Pangaea in Jurassic and diversification of mammals and flowering plants. Therefore 4.5 billion years reflects major division or event in deep time framework. This concept integrates genetics, ecology and molecular evidence, frequently tested in NEET, GATE and CSIR-NET, highlighting links between genotype, phenotype
Ref: USGS, Geological Time Scale, Eons and Eras.