Beyond Hades

Some scientists are asking what the Earth’s climate was like before it became the Earth.  Don’t laugh; they may seem to have too much time on their hands, but believe me, they’re serious.  The Earth formed about 4.6 billion years ago when a cloud of gas imploded, creating dust grains and a star, which exerted gravitational attraction on nearby objects, getting larger and larger as it did, and causing more and more violent encounters, the most notable of which is the moon.  Few rocks have been found older than 3.8 billion years, which demarcates Earth’s earaliest geological eon, known as the Archaean.  Succeeding eons are called the Hadean and the Chaotian, and scientists have proposed several others:  the Nephelean, Erebrean, Hyperitian, and Titanomachean.  Why extend geological history to the pre-rock, pre-planet era?  First, having an established, agreed upon vocabulary can be useful.  Second, if the solar system is to be understood as the result of the events and processes that created it and continue to energize it, it needs a timescale that encompasses its entire history.  Similarly, to see the Earth in the cosmic context of the processes that formed and sustain it, rather than just as bits of stuff, can powerfully alter our attitudes toward it and how we treat it.