The n-Category Café

Some other typos:

The astophysicist Robin Canup has done some remarkable computer simulations of the Big Splat.

The Oxygen Catastophe marks the end of the Archean

characterized by signicant human impact on ecoystems and climate

Thanks for catching those typos, Alex. I’ve fixed them.

I’ve fixed them.

But you've still got ‘there in interesting physics’ instead of ‘there is interesting physics’.

Rod wrote:

First ‘Creationists’ have a problem understanding how the Earth naturally formed.

The magazine Physics World is published by the Institute of Physics, the main British physics organization, which began life as the Physical Society in 1874. I think the readers of this magazine are mainly physicists. So, I don’t think my job here is to persuade creationists.

Thanks for your other comments! This article is based on my earlier article about “mineral evolution” so it says a bit more about rocks than strictly necessary. I’ll think about whether that’s good or bad…

By the way, I wanted to distinguish between granite and basalt, the two most common types of rock. Both are made from molten rock, but basalt is “primitive” while granite is “sophisticated” — it’s made from the remelting of sedimentary rock, so it could only appear after there were oceans, roughly half a billion years after the Earth formed. In fact, it probably took 1.5 billion years for granite formation to really get going, since that’s when plate tectonics got rolling, which pushed ocean plates down in the mantle where they remelt.

John actually answered this nicely, but as a “Creationist” I want to add that while religion is about truth, physics is about models which explain experiment. IMHO John is right not to go there.
And since the article is for people interested into physics, I think people reading it are more interested in explaining observations than in unobservable theological truths, and one needn’t turn science into a political tool.
Indeed, I thought maybe the last paragraph was overstated, because global warming is a politically volatile issue- and not directly relevant to the content of the article. I would cut that part out. It has nothing to do with physics, for one thing…

So chondrites can be formed either by accretion of chondrules with unspecified other stuff? or by collision of planetesimals?

How was dust circling the sun melted by those energetic jets from the POLES?

David wrote:

I thought it was 5:2.

Yikes — you’re right! How embarrassing. There’s a nice description of the Nice model on Wikipedia, but it didn’t say anything about Jupiter and Saturn going from a 2:1 resonance to a 5:2 resonance, so I got lulled into thinking they stayed in the 2:1… even though I’ve known they’re now in a 5:2.

From week222:

The orbits of Jupiter and Saturn are almost in 5:2 resonance, but this is a “shallow” resonance, and Saturn wiggles back and forth around this resonance with a period of about 880 years - an effect called the “Great Inequality”. The first person to study this was Laplace. I read elsewhere that:

The dynamics of the Sun-Jupiter-Saturn system was recognized as problematic from the beginnings of perturbation theory. The problems are due to the so-called Great Inequality (GI), which is the Jupiter-Saturn 5:2 mean-motion near-commensurability.

This is from:

30) F. Varadi, M. Ghil, and W. M. Kaula, The great inequality in a planetary Hamiltonian theory, available as chao-dyn/9311011.

This shallow 5:2 resonance is related to the continued fraction

1/(2 + 1/(2 + 1/(14 + 1/(2 + …. ))))

which is close to 2/5.

The Pluto-Neptune 3:2 resonance, on the other hand, is a “deep resonance” and related to the continued fraction

1/(2 - 1/(2 + 1/(10 + …. )))

which starts out close to 2/3.

I never did manage to fully understand the difference between a shallow resonance and a deep one. But anyway, thanks a lot!

David wrote:

Is that not just a little too casual?

It was an attempt at humor.

Who is the ‘us’ there?

I need oxygen, and so do you.

And what do you mean by ‘now’?

Okay, I should be clearer.

Alas, I said “Please don’t ask me to cover more material: there just isn’t room!” I wanted to talk about theories of the origin of life, but I decided that it wasn’t good to quickly summarize them. I can imagine including them and leaving out the Oxygen Catastrophe, especially since I know of more work by physicists on the origin of life than on the Oxygen Catastrophe. But I think I’ll see what the editor says.

“Abiogenesis for Physicists” would make fascinating reading, but I guess we’ll just have to be patient! :-)

No need to wait, Blake — try this.

When we get time we should try some of these more technical papers:

• Morowitz, H. J. 1999. A theory of biochemical organization, metabolic pathways, and evolution. Complexity 4:39–53
• Smith, E., and H. J. Morowitz. 2004. Universality in intermediary metabolism. Proceedings of the National Academy of Sciences of the U.S.A. 101:13168–13173.
• Morowitz, H. J., and E. Smith. 2007. Energy flow and the organization of life. Complexity 13:51–59.
• Srinivasan, V., and H. J. Morowitz. 2009. The canonical network of autotrophic intermediary metabolism. Biological Bulletin. In Press.

Thanks for the links. For my own webpages I always try to eventually put copies of the necessary images on my own website, since I don’t trust anyone else to maintain them forever.

(I’m not eternal either: I have no idea what’ll happen to my website when I die. I should start working on this issue, but this sort of thing is very easy to put off, since I won’t be around when it matters. Someday there will be big businesses that promise to maintain people’s websites after they die, but so far it’s hard to know who to trust.)

The folks at PhysicsWorld are aware of copyright issues, and will obtain the legal right to use any images they decide to use. But you’re right, their job will be made easier if I let them know the Wikimedia Commons URL’s. So thanks again!

I hope the folks at PhysicsWorld will also draw a nice timeline for me. They said I can put a PDF of the final version of my paper on my website. Someday I’ll give links to that here.

Having your own copies of the pictures seems like a good idea (and I see that you've already done so for one of them), but I also think that you ought to link directly to the Wikimedia versions too. For one thing, this complies (for the two for which this is relevant) with the Creative Commons licence; for all of them, it provides more complete information about where the image came from. (Of course, one might link from the image itself, from some text like ‘(source)’ in the caption, or wherever.)

Just to follow up, there was a Nature article about this last July. One of the authors uploaded it here (pdf). I should note that the zircon crystals containing the diamonds were formed at least 4250 Mya, but I guess they couldn’t put dates on the diamond inclusions they sampled (which, they argue, must have been formed earlier).

Thanks for the info. I’m not succeeding in accessing that PDF file right now, but I’ll check out the Nature article. Thanks for the information! I’ll have to figure out how this modifies the story I’m telling here, if at all.

Cool! Thanks for pointing that out!