Which broad sequence best integrates the major stages in Earth’s evolution?

Correct answer: Accretion and heating → internal differentiation → loss of the early hydrogen-helium atmosphere → outgassing → cooling and formation of the hydrosphere → chemical evolution and life → rise of oxygen through photosynthesis → formation of the ozone layer

Option A gives the broad order from Earth’s formation to later atmospheric and biological change. As Earth accreted, heating led to differentiation; the early hydrogen-helium atmosphere was lost, and gases released from within Earth contributed to a later atmosphere. Cooling allowed water to collect as a hydrosphere. Chemical evolution preceded life, and oxygen-producing photosynthesis later raised atmospheric oxygen, allowing the ozone layer to form. These stages overlap in places, so this is a broad sequence rather than a precise timeline.