Earth History: A Journey In Space And Time

The history of the Earth began exactly 13.7 billion years ago, with the occurrence of the Big Bang.
Pleonastic statement and therefore difficult to refute, since EVERYTHING that exists in this part of the universe – nothing excluded – was born at that precise moment. Even the smallest particle of matter that is now part of the Earth, maybe ended up in a molecule in the eye of a swallow or on top of the Andes Mountains, was formed 13.7 billion years ago.

And it has come down to “us” through twisted and mysterious ways. As mysterious are the transmutations that every molecule of our body had to endure before arriving here to open our eyes to that universe from which we come.
“We are made of the same stuff as the stars,” indeed wrote astronomer and popularizer Carl Sagan many years ago. But now we know that half of that “dust” comes from stars far, far away, even outside our galaxy.
But if everything started at the moment of that famous “T with zero”, it remains curious to know at least a couple of things: when did the universe begin to resemble what we know today? And ultimately, when did galaxies, particularly ours, and then stars and Earth form?

A few seconds after its birth, all the existing must have had the consistency and appearance of a hot primordial soup of particles, especially electrons, protons and photons of light: a kind of opaque fog, where photons could not travel significant distances without colliding with electrons, just as a ray of light in a fog bank is immediately intercepted and spread by some droplet of water in suspension thus forming the typical “wall effect”.
For this reason, this phase is called “Dark Age of the Universe”, lasted until 380.000 years after the Big Bang, all space suddenly became “transparent” to light radiation. From that moment on, in fact, in an environment where the temperature had dropped a lot, facilitating the combination of electrons and protons in the first hydrogen atoms, collisions between particles became extremely rare and photons began to travel freely.

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