O brave new world!

Lord Kelvin challenged Hutton's count of years
as if our planet couldn't be that old
the first among his scientific peers
insisted magma would long since grow cold
sir Isaac's clockwork world would have run down
if not for fission cooking in its core
the physics world had a new boy in town
to overturn what had seemed settled lore
the heavy elements that over-shot
the minimum where iron settles out
can keep a planet's core aslosh and hot
'though no one 'til then knew what that's about
new physics left old scientists behind
who thought they'd mapped the frontiers of the mind