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How old could alien civilizations be?

11 May 2017, 17:34 UTC
How old could alien civilizations be?
(200 words excerpt, click title or image to see full post)

Guest post by Sarah Pearson, Columbia Astronomy Graduate student and creator of the Space with Sarah YouTube channel (www.youtube.com/spacewithsarah). Today Sarah is describing her latest YouTube episode.
Within the last couple of decades, humans have detected thousands of planets around stars other than our own Sun (exoplanets). The enormous number of galaxies each with billions of stars which statistically all have a planet orbiting them, makes it weird to think that life here on Earth should be the only life that exists in the entire Universe.
A question which hasn’t received that much attention yet is: how old could the oldest planetary system be?
We know that our own solar system is roughly 4.6 billion years old, which is actually quite young compared to the whole Universe which is ~13.8 billion years old. The Big Bang, mostly produced Hydrogen and Helium, while Earth’s crust consists mostly of oxygen, silicon and iron. This means Earth couldn’t have formed right after the Big Bang. But for how long would we need to wait?
To create the elements that rocky planets like Earth consist of, stars in the Universe actually need to first be created and then die to spread elements heavier than ...

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