SLIDE 4.
A billion years have
passed since the sun ignited, and the stellar nursery of gas and
dust has been swept clean by a fleet of new-formed planets. There
has been some bickering—in the late heavy bombardment triggered by
the outward migration of Neptune, entire planetary surfaces were
re-formed—but now the system has settled into long-term stability.
The desert planet Mars is going through the first of its warm, wet
interludes; Venus still has traces of water in its hot (but not yet
red-hot) atmosphere. Earth is a chilly
nitrogen-and-methane-shrouded enigma inhabited only by primitive
purple bacteria, its vast oceans churned by hundred-meter tides
dragged up every seven-hour day by a young moon that completes each
orbit in little more than twenty-four hours.