WELCOME to the Y11 EVOLUTION wiki ~ all about CHANGE

Below you will find links to 18 definitive events, people, or scientific technologies that have contributed to our understanding of how we came to be here and where we may be directing life on our planet.
This wiki is based on Chapter 2, "Life's Salient Mystery", from the book, "The Sixth Extinction" by Richard Leakey with Roger Lewin, published in 1995 (Doubleday)

  • 4600 mya (million years ago) our earth condensed from the debris of the early solar system. It was a mass of molten, searingly hot, radioactive rock.
  • Around 3750 mya photosynthetic prokaryotes proliferated and diversified in type. In time, they created the characteristic stromatolite which we can still view living in Shark's Bay, Western Australia, today.
  • For 2 billion years, prokarotes remained the most complex form of life, until some 1800 mya eukaryotic cells finally appeared.
  • It was not until some 530 mya that finally bizarre, complex multicellular organisms devloped in the sea, in an event that paleontologists call the Cambrian explosion.
  • It was during the Cambrian explosion that the probable founder of Phylum Chordata (vertebrates) appeared: a tiny marine worm, with the scientific name Pikaia which anatomically was very similar to Amphioxus, a marine creature alive today.
  • The Cambrian explosion puzzled Charles Darwin, as it challenged his Theory of Evolution. He conceived natural selection as a gradual change (not an explosion), the accumulation of tiny modifications in behaviour and anatomy over time as a response to the environment.
  • Darwin found consolation in the imperfect fossil record and argued that evidence of the ancestors of the Cambrian explosion had yet to be found.
  • Almost a century had to pass before the Australian geologist, R. C. Sprigg discovered evidence for multi-celluar life prior to the Cambrian explosion, in the Ediacara Hills of the Flinders Range in South Australia. These deposits of soft-bodied organisms, the Ediacaran Fauna, were in rocks dating (Dating Rocks) from around 670 mya.
  • Darwinism seemed saved. Here was evidence of ancestors to Cambrian life from which it would have developed. And they had developed at a time when the earth's physical environment changed and the oxygen barrier (1% to 20% oxygen in the atmosphere) preventing the emergence of multicellular life was removed. (Earth's Oxygen Atmosphere)
  • Several more decades passed and then doubts arose, presented in part by the influential Adolf Seilacher who acknowledged that there were superficial resemblances between Ediacaran species and later fauna, but that the transport systems of the two sets of animals were completely different.
  • Seilacher's view soon prevailed. In 1993 Simon Conway Morris published a diagram in Nature showing the Ediacaran explosion followed by its eclipse, with no link to the Cambrian explosion.
  • About 555 mya the Ediacaran fauna disappeared, almost without trace, ancestors of nothing, a great failed experiment in evolution. This was the first of the The Five Mass Extinctions of life on earth.
  • Darwinism was not saved. That the explosion of life in the Cambrian era emerged, was once again an enigma, which has been termed, "life's salient mystery".

Leakey and Lewin have written a book on evolutionary change. They present a discussion in which they see Homo Sapiens as only a small moment in the great continuous flow of life and argue that as it has become THE dominant species on the planet, it may be in the process of causing the The Sixth Extinction.

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Y11 Evolution bibliography