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Chapter Nineteen — The Rise of Life

A Short History of Nearly Everything – by Bill Bryson

Chapter 19 — The Rise of Life

  • Of the billions of species of living things that have existed since the dawn of time, 99.99% are extinct.
  • Proteins are what you get when you string amino acids together, and we need a lot of them.  One really knows, but there may be as many as a million types of protein in the human body.
  • Proteins are very complex entities.  Hemoglobin is only 146 amino acids long, a runt by protein standards, yet even it offers 10190 possible amino acid combinations.
  • DNA can make a copy of itself in seconds, but can do virtually nothing else.  So we have a paradoxical situation.  Proteins can’t exist without DNA, and DNA has no purpose without proteins.
  • Richard Dawkins proposes that there must have been some kind of cumulative selection process that allowed amino acids to assemble in chunks.  Perhaps two or three amino acids linked up for some simple purpose and then after a time bumped into some other similar small cluster and in so doing “discovered’ some additional improvement.
  • Many scientists now believe that life many be more inevitable than we think, that is, “an obligatory manifestation of matter, bound to arise wherever conditions are appropriate.”
  • If you wished to create another living object, whether a goldfish or a head of lettuce or a human being, you would need really only four principal elements — carbon, hydrogen, oxygen, and nitrogen, plus small amounts of a few others.
  • How early in Earth’s history did life arise?  By the 1970’s some felt that life dated back 2.5 billion years.  The present date of 3.85 billion years is stunningly early.  Earth’s surface didn’t become solid until about 3.9 billion years ago.
  • The Murchison meteorite, discovered in Australia, was found to be 4.5 billion years old, and it was studded with amino acids – 74 types in all, 8 of which are involved in the formation of earthly proteins.
  • It is now thought that about 25% of Halley’s comet is organic molecules.
  • Whatever prompted life to begin, it happened just once.  That is the most extraordinary fact in biology.  Everything that has ever lived, plant or animal, dates its beginnings from the same primordial twitch.  At some point in an unimaginably distant past some little bag of chemicals fidgeted to life.  It absorbed some nutrients, gently pulsed, had a brief existence. This ancestral packet then cleaved itself and produced an heir.  A tiny bundle of genetic material passed from one living entity to another, and has never stopped moving since.
  • If you are into very old rocks, the Australian National University is a prime place to be.  It is there that the world’s first Sensitive High Resolution Ion Micro Probe (SHRIMP) machine was built.  This machine measures the decay rate of uranium in tiny minerals called zircons.  On its first formal test in 1982, SHRIMP dated the oldest thing ever found – a 4.3 billion-year-old rock from western Australia.
  • At some point in the first billion years of life, cyanobacteria, or blue-green algae, learned to tap into a freely available resource – the hydrogen that exists in spectacular abundance in water.  They absorbed water molecules, supped on the hydrogen, and released the oxygen as waste, and is so doing invented photosynthesis.  As cyanobacteria proliferated, the world began to fill with oxygen to the consternation of those organisms that found it poisonous (almost all of them).  The cyanobacteria were a runaway success.  At first, the extra oxygen they produced didn’t accumulate in the atmosphere, but combined with iron to form ferric oxides, which sank to the bottom of primitive seas.  For millions of years, the world literally rusted.
  • It took about two billion years, roughly 40 percent of Earth’s history, for oxygen levels to reach modern levels of concentration in the atmosphere.  The oxygen level in our cells is only about one-tenth the level found in the atmosphere.
  • About 3.5 billion years ago, visible structures began to appear in shallow seas.  The cyanobacteria became slightly tacky as they went through their chemical routines, and that tackiness trapped micro-particles of dust and sand, which became bound together to form slightly weird but sold structures – stromatolites.
  • Mitochondria manipulate oxygen in a way that liberates energy from foodstuffs.  Without this facilitating trick, life on Earth today would be nothing more than a sludge of simple microbes.  Mitochondria are very tiny – you could pack a billion into the space occupied by a grain of sand – but also very hungry.  Almost every nutriment you absorb goes to feeding them.
  • Gradually a system evolved in which life was dominated by two types of life-form – organisms that expel oxygen (like plants) and those that take it in (you and me).

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