Actually not a surprise if one lives in TGD Universe. TGD predicts that all astrophysical objects, including planets, might have experienced this kind of periods. In general relativity these periods would correspond smooth cosmological expansion of this objects: the absence this smooth expansion is indeed an enigma - astrophysical objects co-move with expanion in large scale but do not expand themselves. Earth would have experienced this expansion during Cambrian explosion.
The underground oceans would make possible evolution of life without problems from cosmic rays and meteorites and radioactivity (for instance) could provide the metabolic energy.
This would solve Fermi's paradox: most planets could be carriers of intraplanetary invisible-to-outsider life waiting the next fast expansion and burst to the surface of the planet.
See http://tgdtheory.fi/public_html/articles/expearth.pdf .
For a summary of earlier postings see Latest progress in TGD.