February 3, 2014 – Biology
History of life on earth: Chapter 25
• Earth is 4-5 billion years old
• The decay of the isotopes in surrounding sediments provides a signal of approximate
• Alberta Ammonite fossile: ammonite is complete extinct.
• History is presented is linear,
• Paleontology: looks at the history of life on earth. Royal Terrell Museum shows fossils
mostly found in Alberta.
• What do fossil tell us about life? What led to extinction? How old is it?
o Magnitude of change has been enormous
o Extinction is a common feature (99% of all organisms?)
o Pace of evolution and natural selection
• How can we estimate ‘age’ : decay of isotopes on sediments
o Radiometric dating of sediment (not fossils), nitrogen, carbon
• Macroevolution: pattern of evolution above the species level, over very long time periods
o Origin of prokaryotes (not long after the creation of the solar system)
o Origin of eukaryotes, natural selection favors a nucleus.
o Origin of multicellularity the constraints of having one cell led to multicell
o Origin of animals
o Origins of other taxa
o Mass extinctions (5 or 6 of them) are we currently in a 6 mass extinction event?
o Figure 25.1: geologic record. be familiar with it, general aware of the length of it
(4-5 billion years)
o Figure 25.7 is very important! Geological clock, must know the key words
Hypothesis for the origin of life
• Book supports one hypothesis
• The nature of indirect evidence (will be able to understand more about the origin if we
can find another planet with life on earth)
• When and how did first cells (and their precursors) appear? • Chemical processes + physical processes + natural selection = life
o What is life?
Metabolizing energy (using energy for its own needs)
• Propose 4-stage process: ultimately leads to potential life
o 1. Synthesis of organic compounds creating something more complicated
Earth’s early atmosphere
• Water vapor
• Nitrogen, CO 2 Methane, Ammonia
o Miller-Urey experiments (1953) Figure 4 (Chapter 4)