Timescale Of Life

Life has been on earth for ~3.8 billion years. We've identified 1.8 million species so far, and we estimate there are 10-100 million actually out there (mostly insects).



Fossils are a good way of examining previous life, except that the fossil record is biased in favour of species that:

  • Existed for a long time
  • Were abundant and widespread
  • Had hard/solid parts
  • Existed in the last 3 billion years (is how long fossils survive)

Unity/Diversity of Life

Throughout these nearly 4 billion years, there would seem to be a lot of diversity in lifeforms. Yet when you look at it, the cilia of a single-celled organism and of a windpipe have the same cell structure. It appears we have common consistent base building blocks (cells).


Darwin's 4 Laws:

  1. Individuals within a species are variable
  2. Some variants are passed onto offspring
  3. Each generation produces more offspring than can survive
  4. Therefore there is a kind of natural selection happening.

Drake's Law

Everytime a living organism or virus replications, one mutation is made.

High Diversity

High diversity allows for rapid evolution. This is how viruses and bacteria can mutate so fast.