Final answer:
The Hadean Eon began 4.6 billion years ago, subsequent to the Big Bang, which occurred about 13.7 billion years ago. This eon does not mark the universe's inception but denotes an early period on Earth characterized by high temperatures and later the first signs of life.
Step-by-step explanation:
The Hadean Eon began about 4.6 billion years ago, representing the time after Earth's formation, which followed the Big Bang event that occurred approximately 13.7 billion years ago.
The commencement of the Hadean Eon does not mark the beginning of the universe, rather it denotes an era in Earth's early history which was characterized by the planet being extremely hot and inhospitable.
The Big Bang theory describes the beginning of the universe as an expansion from an extremely hot and dense state, eventually leading to the formation of galaxies, stars, and planetary systems like our own. The Hadean Eon witnessed Earth's initial cooling, paving the way for the eventual origin of life.
The timeline of the universe began with the expansion from the Big Bang, followed by the formation of basic particles and atoms, the coalescence of matter to form stars and galaxies, and then the solar system with our Sun.
On this timeline, Earth formed around 4.6 billion years ago, and the first signs of life appeared during the Hadean or immediately afterwards. The universe itself, being much older, is a testament to the vast stretches of cosmic time that precede even the earliest moments of our planet's history.
In summary, the universe's inception is credited to the Big Bang, and the hot, dense, isotropic, and expanding state of the early universe is corroborated by the cosmic background radiation. Over time, the universe evolved to form stars and planets, including Earth, which developed conditions suitable for the emergence of life within the Hadean Eon.