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Just Chat! / Irony

« on: 16/02/2013 22:09:52 »

When I joined these forums a year or two ago, I chose the name Damocles. The sword that I could see poised over my head, and indeed all of our heads, was carbon dioxide build up in the atmosphere. If the most likely consequence of this -- global warming -- does not eventuate, there will be some other equally drastic one. One cannot change natural systems as much as we have changed the CO2 levels without causing trouble.

But it turns out there was another sword poised over my personal head. Following an episode where I lost the ability to communicate, the medicos found a brain tumour. I start radiotherapy on Tuesday, with the prospect of about 6 months to 5 years to live! So I have been absent from the forums during a stay in hospital, and will probably be absent from now on. Farewell all! It has been good to know you and to cross swords with you in debate.

I am about to find out whether my religious faith has been misplaced or not, but unfortunately I will not be able to report back.

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Chemistry / Chemical Mystery of the origins of Life

« on: 13/09/2012 03:30:11 »

In a thread in the Physics forum on the origins of life on Earth JP has written:

There are definitely some rough connections you can draw from the big bang to the formation of the elements for example, and from the formation of the elements to inorganic chemistry, then from inorganic chemistry to the formation of amino acids (I'm thinking of the Urey/Miller experiment here, but I know there's been other work on it), which would likely be a path to organic chemistry.

Are there still any specialist scientists (as opposed to speculative physicists) who still see the Urey/Miller experiment (and subsequent work in that tradition) as at all relevant?

Firstly, there is ample chemical and geological evidence that the atmosphere of the Earth at the time that life got started on Earth contained neither ammonia nor methane.

Some quotes from Wayne's scholarly monograph "Chemistry of Atmospheres", Chapter 9.4

Access to the detailed geological record for Earth constrains speculation about our ancient atmosphere (palaeoatmosphere) and its development ...
Strongly reducing atmospheres of CH4 and NH3 must have been very short-lived, even if they existed at all ... {NH3 is rapidly photolysed -- lifetime 2-3 yr, and subject to rainout -- lifetime 10 days; CH4 is subject to attack by OH radicals from water photolysis -- lifetime ~ 50 yr}...
No known chemical processes generate either CH4 or NH3 in the atmosphere, and hydrocarbons (including CH4) in geothermal emanations are ultimately of biological origin, according to carbon isotope measurements. ...
The rock record begins 3.8 Gyr ago with highly metamorphosed sediments at Isua in West Greenland. These rocks were formed in the presence of H2O and CO2, but without abundant CH4 ... (etc.)

Secondly, there is also considerable evidence that the earliest forms of life on Earth were thermophile microorganisms in colonies near undersea vents. It is in any case nearly impossible for life to have existed in the atmosphere in these early times because of the unattenuated solar ultraviolet radiation in the 200-300 nm wavelength region which would break C-N, C-C, and C-O bonds in polyatomic organic molecules randomly and rapidly. Lightning arcs are unlikely to occur under an electrolyte ocean.

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Physics, Astronomy & Cosmology / So what is the output of the Sun relative to the heat we receive on Earth?

« on: 19/02/2012 00:36:12 »

Yor-on (from another thread: "What's wrong with thermodynamics?") asks:

So what is the 'output' of the sun relative the heat/IR we receive on Earth? I guess it might be difficult to answer that one but it would be interesting to know the relation between those two. If we talk about photons the only way they 'annihilate' is through interactions, if we talk about waves we have quenching and reinforcing. And the waves from the sun are polychromatic, of a lot of different wavelengths. So how do the transfer of heat works, and if some get lost, to what does it lose?

In some ways the answer to that one is surprisingly easy! When it reaches the Earth, the total radiation output of the Sun is, to a good approximation, uniformly spread over the surface of a sphere with radius equal to the distance from Sun to Earth -- roughly 150 million km. The total surface area of this sphere is 4 x π x (1.5E11)² m² = 2.8E23 m².

The cross-section area of the Earth's disk that intercepts some of this light is given by π x (radius of Earth)^2, and the radius of the Earth is around 6500 km.

π x (6.5E6)² m² = 1.33E14 m².

The proportion of the total solar output that is intercepted by the Earth is therefore 1:2E9 -- about one two billionth!

When the Earth intercepts solar radiation, there are lots of complicated physical and chemical processes that might follow, but they really amount to two things -- either the radiation is absorbed somewhere in the Earth system, or the radiation is reflected back into space. The proportion that is directly reflected is known as the "albedo", and the Earth's albedo is around 36%. The other 64% is absorbed and used by various Earth systems. As usual the actual situation is just a little more complicated because the albedo is wavelength dependent -- the reflection/absorption balance differs for different wavelengths of solar radiation.

------

That is a fairly complete simple answer, but it is really necessary to expand it with a summary of the rest of the story. Obviously the Earth does not just keep on absorbing solar radiation, or it would just keep getting hotter and hotter! The Earth (and any other hot body) radiates on its own account, and in doing so it loses energy and cools itself. A balance is reached when the heat gain from absorbing solar radiation is exactly matched by the emission of the Earth's own radiation.

The hotter a body is, the more power output, and the shorter the wavelength average of its radiation spectrum. A metal looks black when we can feel its infrared radiation, but if it gets a little hotter we will see it radiate visible red light (red hot), and at higher temperatures yellow, and then white light.

The sun's radiation is mostly in the visible region, with a peak output in the green part of the spectrum -- near the middle of the visible. That is a wavelength of about 0.52 µm. The Earth's radiation is infrared, with a peak wavelength around 16 µm. Emission of radiation is governed by the same albedo factor as absorption: the more reflection and the less absorption, the less the emission will be.

The normal average surface temperature of a planetary body at the Earth's position in the solar system can fairly readily be calculated: it works out at -20°C, and that is roughly correct for the moon. The Earth is (fortunately) warmer, with an average surface temperature of 16°C, as the result of several complicating factors. The most important of them arises from the presence of water clouds, and water vapour in the atmosphere.

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That CAN'T be true! / Examples of weird, amusing, or ambiguous headlines/article titles in science.

« on: 16/02/2012 07:25:19 »

I am interested to know if any of you have come across and been amused by such things.

As an example, one of my favourites has been an article in a new age, green, do-it-yourself magazine entitled

"Build Your Own Solar System".

(I think they were talking about hot water or electricity generation).

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That CAN'T be true! / Hairy donuts and spherical dogs?

« on: 24/07/2011 10:15:07 »

An allegedly important result in topology -- you cannot comb a (long-haired) spherical dog without producing at least two crowns or cowlicks. It is a simple matter, on the other hand, to comb a very hairy donut without producing a crown or cowlick.

Heard about this result many years ago, and intuitively it seems right, but I have not managed to find a reference on the web.

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That CAN'T be true! / Renewable Energy?

« on: 14/07/2011 15:27:01 »

Headline observed in a local conservation/sustainable lifestyle magazine:

"Build Your Own Solar System"

I know what was meant, but ... well... really?!!