Unless you have a degree in geology
or paleontology or something similar, you are probably as confused by the
various Ages, Eons and Periods that get named when you look anything up about
the History of Earth. I decided to take a look at one of them, and see if I
could get it figured out as to when it happened, what major events happened
during it... that sort of thing.
So, I had a list of these names, and
I picked one at random: the Hadean Eon.
Turns out, I had picked the very
first of Earth’s Eons; it started with the formation of Earth about 4.6 billion
years ago and ended approximately 4 billion years ago. Other names for it are
the Priscoan Period and the Pre-Archean Eon.
Obviously, since we are looking at
the very first half billion years of the world, we won’t be talking about
dinosaurs or super continents. What could there possibly be to discuss? Well,
let’s dig in and see what turns up.
First, there’s the name, which gives
us a clue about what was going on. ‘Hadean’ comes from Hades, the Greek god of
the underworld. And that describes the conditions of what Earth was going
through: The planet had just formed and it was very hot due to a number of
factors, including frequent collisions with other Solar System bodies.
One important collision happened
about 4.5 billion years ago, when a Mars-sized planetoid smashed into the
infant Earth. The collision sent quite a lot of material into orbit around
Earth, while the planetoid and the rest of Earth merged and tried to settle
down. The orbiting material probably took less than a century to form the moon.
The big collision didn’t melt all of
the Earth, but a fair fraction of material was vaporized, which created a rock
vapor atmosphere around the young planet. But that rock vapor would have condensed
out within 2,000 years, and left behind an atmosphere heavy in CO2 with some
hydrogen and water vapor.
Apparently, there was a sizable
quantity of water in the material that formed the Earth. After the moon was
formed, the surface temperature was about 230C (446F), but even so, oceans of
liquid water existed. That’s because the atmospheric pressure was over 27 times
what it is today, because of the heavy CO2 atmosphere. As cooling continued,
most of the CO2 was removed from the atmosphere by subduction and dissolving in
ocean water, but the levels oscillated wildly.
One theory posits that between 4.4
and 4.1 billion years ago, the Earth’s climate was relatively cool, allowing
for liquid water to be present at least
that long. It was even suggested that the Earth may have been pretty much like
it is today, except for the absence of flora and fauna.
One of the articles implied that
life may have been getting started by the end of the Hadean Eon. But that was
almost like a throw-away at the end of the last paragraph, so I’m thinking ,
one celled organisms? Maybe?
So as far as stories go, what if a
spaceship gets too close to a forming star system and gets clobbered by tiny
planetoids until it is forced to crash land on the nearest planet, which just
happens to be vaguely Earth-like, but the only life it has are some quasi-amoebas
swimming in the oceans. Maybe they have plants or seeds aboard, so they can
grow some food. What about the stuff they don’t realize they’re carrying?
Cockroaches, mice, fungal spores... What would those things evolve into, once
there was enough food on the planet for them to successfully venture off the
ship? There would be a whole lot of niches in the food chain for them to fill!
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