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ashone10 (Getting the Lead Out ** )

Chapter Ten — Getting the Lead Out

A Short History of Nearly Everything – by Bill Bryson

Chapter 10 — Getting the Lead Out

  • Lead is a neurotoxin.  Get too much of it and you can irreparably damage the brain and central nervous system.  Among the many symptoms associated with overexposure are blindness, insomnia, kidney failure, hearing loss, cancer, palsies, and convulsions.  In its most acute form it produces abrupt and terrifying hallucinations, which can give way to coma and death.
  • In 1921, Thomas Midgley discovered that engine ping or engine knock could be greatly reduced by adding tetra-ethyl lead to gasoline.  Workers in the production plants where tetra-ethyl lead was produced almost immediately began to experience many or all of the symptoms of lead poisoning.
  • Thomas Midgley was also instrumental in discovering chlorofluorocarbons.
  • Beneficial ozone is not terribly abundant.  If it were distributed evenly throughout the stratosphere, it would form a layer just one eighth of an inch thick.
  • Chlorofluorocarbons (CFCs) destroy ozone.  One pound of CFCs can capture and annihilate seventy thousand pounds of atmospheric ozone.  CFCs also hang around for a long time – about a century on the average – wreaking havoc all the while.  They are also great heat sponges.  A single CFC molecule is about ten thousand times more efficient at exacerbating greenhouse effects than a molecule of carbon dioxide – and carbon dioxide is of course no slouch itself as a greenhouse gas.  In short, CFCs may ultimately prove to be just about the worst invention of the 20th century.
  • Carbon-14 has a half-life of about 5,600 years.  A half-life is the time it takes for one-half of any sample to disappear.  By working out how much a given sample of carbon had decayed, scientists could get a fix on the age of an object.  This dating method has limitations, however.  After 8 half-lives, on 1/256 of the original radioactive carbon remains, which is too little to make a reliable measurement, so radiocarbon dating works only for object up to forty thousand or so years old.
  • It was also quickly discovered that carbon-14 samples can be easily contaminated with carbon from other sources — a tiny scrap of vegetable matter, for instance, that has been collected with the sample and not noticed.
  • Also, carbon dating readings can be thrown off by seemingly unrelated external factors, such as the diets of those whose bones are being tested.
  • Arthur Holmes discovered that potassium-40 decays into argon-40.  If you measure the amounts of both substances in a sample, you can work out how old the sample material is.
  • Clair Patterson developed a method of measuring minute quantities of uranium and lead locked up in ancient crystals.  Using this method, he announced a definitive age for the Earth of 4.55 billion years, plus or minus 70 million years.  This figure stands virtually unchanged to the present time.
  • Patterson also discovered that before 1923, there was almost no lead in the atmosphere, and that since that time (when lead was added to gasoline) the lead level had climbed steadily and dangerously.  He made it his life’s quest to get lead taken out of gasoline.

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