The Great Filter

John K Clark (
Sun, 25 Aug 1996 18:07:47 -0700 (PDT)


On Sat, 24 Aug 96 (Robin Hanson) Wrote:

>>Earth formed about 4.6 billion ago, but life didn't
>>have a chance for it's first billion years or so,
>>it was far too hot and the Earth suffered impacts
>>so large it would make the one that killed the
>Dinosaurs look like a joke.

>Do you have a source re the actual temp vs. time curve?

No I don't, I doubt if anybody has precise enough knowledge to make such a
curve. My statement that the early earth must of been hot was based on the
following. The Earth was formed by a very large cloud of particles, this
cloud must have possessed a lot of potential gravitational energy. When the
Earth coalesced this potential energy was gone and was replaced by heat
energy, a LOT of heat energy, enough that if converted to kinetic energy
could push every atom in the planet away from the center at the escape
velocity of 7 miles a second. A secondary source of heat would come from
radioactive isotopes that the earth must have possessed in much higher
abundance 4.6 billion years ago than today. Radioactive potassium would have
given off the most heat, followed by uranium. Harold Urey calculated that the
radioactivity alone was enough to heat the center of the Earth ( admittedly
not the surface) to 1500 degrees C. The center of the Earth is thought to be
at about 5500 degrees C, the rest of the heat came from the kinetic energy of
in-falling matter.

The fact that not a single rock survives from Earth's first 800 million years
indicates that conditions must have been very violent indeed, but it also
destroys the evidence about exactly how hot it was.

>bacteria are lots hardier than Dinos.

Yes, but are bacteria hardier than rocks, especially the very earliest
bacteria? Also, these bacteria must do more than just survive, they must
evolve from simple chemicals.

>My sources are pretty authoritive (see paper cites), and
>clearly say that Eukaryotic cells appeared about 1.8-2.0 bya
>(billion years ago), when the atmosphere became oxygen
>-dominated after all the ocean's iron was finally oxidized.

Looking through my home library I can find 3 books to support my 1.2 to 1.4
bya claim for the first Eukaryotic cells, "Life Itself" by Francis Crick,
"Origins" by Robert Shapiro (no, not OJ's lawyer), and "Darwin to DNA" by
G Ledyard Stebbins, I found another book "The Rise of Life" by John Reader
that said 1.45 bya. As I mentioned, I do remember reading about a claim for a
later figure, but for the life of me I can't remember where. I suspect that
when you look at tiny fossils that are billions of years old, it's not always
easy to tell if they're Prokaryotes or Eukaryotes.

I agree with your timeline about the appearance of oxygen in the atmosphere,
but I see no reason why only Eukaryotes could have caused it.

John K Clark

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