It was about 4.5 billion years ago. On a hot, and one can say sunny, day – and all days were hot back then – the young planet Gaia almost met its fate. Another planet, we now call it Theia, crashed into Gaia. Through the impact, enormous amounts of rock and gas exploded into space. There, we now believe, they coalesced into a satellite. Planet Earth and its Moon were born. If we would have been around to watch back then, all this cataclysmic events when Gaia became Earth would for us have occurred in utter and total silence. There was no atmosphere that could have transported any sound…
On Earth, however, the explosion had created large amounts of rock vapor that with time condensed into carbon dioxide mixed with hydrogen and water. The first atmosphere had appeared and that, possibly, was the moment sound came to Earth.
(more…)