Best evidence for the view that all oxygen on Earth came from stars:
1. Stellar nucleosynthesis: The process of nucleosynthesis in stars, specifically during their life cycle and explosive death, is responsible for the creation of elements heavier than helium. Nuclear reactions in the core of stars produce oxygen and other elements through fusion processes. This scientific understanding strongly supports the idea that all oxygen present on Earth today was created in different generations of stars.
2. Isotopic composition: Oxygen on Earth consists of three stable isotopes: oxygen-16 (O-16), oxygen-17 (O-17), and oxygen-18 (O-18). Isotopes have unique atomic masses, and their relative abundances carry significant information about the origin of the element. The ratios of these isotopes in terrestrial oxygen match the expected ratios produced by stellar nucleosynthesis. This suggests that the oxygen found on Earth was indeed derived from stellar processes.
3. Supernova enrichment: When massive stars go through their explosive deaths as supernovae, they release enormous amounts of energy and matter into space. These energetic events scatter heavier elements like oxygen throughout the galaxy in the form of gas and dust. Observations of interstellar clouds and circumstellar material support the finding of oxygen-rich compounds derived from supernovae, confirming their role in the creation of oxygen in the universe.
Best evidence against the view that all oxygen on Earth came from stars:
1. Primordial oxygen: During the early stages of the universe, before the formation of stars, oxygen-16 may have been synthesized through different processes such as Big Bang nucleosynthesis. This could potentially account for a fraction of the oxygen present on Earth without being linked to stellar origins.
2. Other cosmic sources: While stars are widely considered as the primary source of heavier elements, other cosmic phenomena like neutron star mergers and black hole collisions could also contribute to the production of oxygen. Although these processes are less understood, they introduce alternative mechanisms for the origin of oxygen that are not directly tied to stars.
3. Local chemical environment: Earth’s atmosphere and geologic processes can also play a role in the local oxygen levels. Volcanic activity, photosynthetic organisms, chemical reactions, and geological weathering processes can all contribute to the oxygen content on Earth. While stellar processes are likely the primary source of oxygen on a cosmological scale, these local factors need to be considered when examining the origin of oxygen on Earth.