ABSTRACT
The universe has dramatically evolved from the chemically poor ashes synthesized a few minutes after the Big Bang during primordial nucleosynthesis. Indeed, the main observable legacy of the Big Bang, aside from the cosmic microwave background, was in the form of relic 1H (75% by mass), 4He (25%), and traces of deuterium (d) and 3He (at the level of ∼ 10−5%), and 7Li (∼ 10−7%; see Figure 2.1(a)). Hydrogen and helium are still the most abundant species in today’s universe1, accounting for ∼ 98% of its mass. But the chemical composition of the human body (Figure 2.1(b)) or of the Solar System itself (Figure 2.2) is far more rich in nuclear species and reveals a complex history.
