Practice question

Ozone forms via photodissociation of molecular oxygen by ultraviolet radiation producing atomic oxygen that combines with O2. Without atmospheric oxygen produced by oxygenic photosynthesis, no ozone could accumulate. Once cyanobacterial oxygen reached threshold, stratospheric ozone layer developed absorbing harmful UV-C and UV-B, protecting biomolecules. This facilitated colonization of land and surface waters. The causal link explains why Accumulation of O2 is prerequisite for ozone shield and subsequent diversification of life. This concept integrates genetics, ecology and molecular evidence, frequently tested in NEET, GATE and CSIR-NET, highlighting links between genotype, phenotype and environment.