–<\/p>\n
Thus there is nothing optimal or ideal about living on an oxygen-
\nrich planet; it is simply the way things turned out. Oxygen is, after
\nall, an extremely abundant element: the third most abundant in
\nthe universe, and the most abundant (47 per cent of the total) in
\nthe Earth’s crust. On the other hand, the living world (the
\nbiosphere) has contrived to maintain the proportion of oxygen in
\nthe atmosphere at more or less the perfect level for aerobic
\n(oxygen-breathing) organisms like us. If there was less than 17
\nper cent oxygen in the air, we would be asphyxiated. If there was
\nmore than 25 per cent, all organic matter would be highly
\nflammable: it would combust at the slightest provocation, and
\nwildfires would be uncontrollable. A concentration of 35 per cent
\noxygen would have been enough to destroy most life on Earth in
\nglobal fires in the past. (NASA switched to using normal air
\nrather than pure oxygen in their spacecrafts for this reason, after
\nthe tragic and fatal conflagration during the first Apollo tests in
\n1967.) So the current proportion of 21 per cent achieves a good
\ncompromise.<\/p>\n
This constancy of the oxygen concentration in air lends support to
\nthe hypothesis that the biological and geological systems of the
\nEarth conspire to adjust the atmosphere and environment so that
\nthey are well suited to sustain life – the so-called Gaia hypothesis.
\nOxygen levels have fluctuated since the air became oxygen rich, but
\nnot by much. In addition, today’s proportion of atmospheric oxygen
\nis large enough to support the formation of the ozone layer in the
\nstratosphere, which protects life from the worst of the sun’s harmful
\nultraviolet rays. Ozone is a UV-absorbing form of pure oxygen in
\nwhich the atoms are joined not in pairs, as in oxygen gas, but in
\ntriplets.<\/p>\n
This smells like the ‘backwards’ thinking that fuels the arguments from design<\/a>. The reason that the oxygen level is ‘just right’ for organisms, is that.. they have evolved to fit the current (or recent ancestral) levels of oxygen in the air.<\/p>\n Also, the claims sound rather fishy, and i cudn’t either confirm or disconfirm when i tried with Wikipedia and Google.<\/p>\n –<\/p>\n And the crowning irony is that gold is the most useless of metals, That doesn’t seem right to me. The symbolism section on Wikipedia<\/a> seems to be pretty much only about indo-european cultures, and no data about, say, pre-contact African cultures. However, after my quick googling around, i didn’t find any more data about this.<\/p>\n –<\/p>\n The metals are the most familiar and recognizable of the chemical Yes, they do. I have seen many such examples. The first three that came to mind are: 1) In Crash Bandicoot games, the player is rewarded with a platinum relic which is better than the gold relic (random video of this<\/a>), 2) In Starcraft 2, the Platinum league is higher (better) than the Gold league<\/a>, 3) in music sales classification<\/a>, platinum is better than gold. I’m sure that there are tons of more examples.<\/p>\n –<\/p>\n \u00a0So how many elements are there? I do not know, and neither does * Elements slightly heavier than uranium, produced by radioactive decay (see I thought that only atoms up to Uranium were natural, but apparently not. Wikipedia<\/a> lists 98 elements that are currently known to occur naturally, either on Earth or in some distant star. I had also conflated natural elements with elements that have at least one stable isotope. However, on reflection i see that i was just wrong, since Radon<\/a> (Rn) occurs naturally but doesn’t have a stable isotope. There are a few other natural elements that also lack a stable isotope (as far as we know, anyway).<\/p>\n –<\/p>\n Polar ice contains tiny bubbles of trapped ancient air, within which
\nprized like a fashion model for its ability to look beautiful and do
\nnothing. Unlike metals such as iron, copper, magnesium,
\nmanganese, and nickel, gold has no natural biological role. It is too
\nsoft for making tools; it is inconveniently heavy. And yet people
\nhave searched for it tirelessly, they have burrowed and blasted
\nthrough the earth and sifted through mountains of gravel to claim
\nan estimated 100,000 tonnes in the past five hundred years alone.
\n‘Gold’, says Jacob Bronowski, ‘is the universal prize in all countries,<\/strong>
\nin all cultures, in all ages.’<\/strong><\/p>\n
\nelements to non-scientists – for everyone senses the uniqueness of
\nstolid iron, soft and ruddy copper, mercury’s liquid mirror. And
\namong these ponderous substances no element has more resonance
\nand rich associations than gold. It is an enduring symbol of
\neminence and purity. The best athletes win gold metals (in a trio of
\nmetals that echoes that of the oldest coinage); the best rock bands
\nwin golden discs. A band of gold seals the wedding vows, and fifty
\nyears later the metal valorizes the most exalted anniversary of
\nmarried bliss. Associations of gold sell everything from credit cards
\nto coffee. Platinum is rarer and more expensive, and some attempts<\/strong>
\nhave been made to give it even grander status than gold. But it will<\/strong>
\nnot work, because there are no legends or myths to support it.<\/strong> There
\ncan be no other element than gold whose chemical characteristics
\nhave been so responsible for lodging it firmly in our cultural
\ntraditions.<\/p>\n
\nanyone else. Oh, they can tell you how many natural elements there
\nare – how many we can expect to find at large in the universe. That
\nseries stops around uranium, element number 92.* But as to how
\nmany elements are possible – well, name a number. We have no idea
\nwhat the limit might be.<\/p>\n
\nlater), are found in tiny amounts in natural uranium ores. Plutonium (element 94)
\nhas also been found in nature, a product of the element-forming processes that
\nhappen in dying stars. So it is a tricky matter to put a precise number on the
\nnatural elements.<\/p>\n
\nscientists can measure the amounts of minor (‘trace’) gases such as
\ncarbon dioxide and methane. These are greenhouse gases, which
\nwarm the planet by absorbing heat radiated from the Earth’s
\nsurface. The ice cores show that levels of greenhouse gases in the
\natmosphere, controlled in the past by natural processes such as
\nplant growth on land and in the sea, have risen and fallen in near-
\nperfect synchrony with temperature changes. This provides strong<\/strong>
\nevidence that the greenhouse effect regulates the Earth’s climate<\/strong>,
\nand helps us to anticipate the magnitude of the changes we might
\nexpect by adding further greenhouse gases to the atmosphere.<\/p>\n
![\"\"](\"http:\/\/imgs.xkcd.com\/comics\/correlation.png\" "\\"Correlation\\"")
<\/p>\n![\"\"](\"http:\/\/chaospet.com\/comics\/2009-12-28-corrr.png\" "\\"Correlation")
<\/p>\n