<i>Where is this 600M years taken from?</i><p>I didn&#x27;t read the paper, but probably this technique: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Molecular_clock" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Molecular_clock</a>