Evolution Warm-up – Part 2
• What is the difference between absolute
(radioactive) dating and relative dating of
fossils?
• What is the difference between
homologous and analogous structures?
The Origin of Life – Early Ideas
• Several centuries ago, the prevailing
idea was abiogenesis, the idea that
nonliving material can produce life
– maggots developed from dead meat
• Francesco Redi disproved this theory in
1668
Biogenesis vs Abiogenesis
• Spontaneous Generation
Francesco Redi’s Experiment
Louis Pasteur’s Experiment
• After Redi’s experiment, many
still thought that air played a vital
part in producing life
• Louis Pasteur conducted an
experiment to disprove this idea
– Filled a flask with broth and boiled
it
– The flask’s neck allowed air to
enter, but not microorganisms
– The broth stayed clear for one
year, after which he tilted the flask
to allow microorganisms to enter
– Soon the broth became cloudy and
contaminated
Louis Pasteur’s Experiment
The Origin of Life – Modern
Ideas
• Biologists have accepted the idea of
biogenesis, thanks to Redi and Pasteur
• However, biologists do not have an
answer as to how life originally began on
Earth
• Many theories deal with spontaneous
origin
– Through chemical reactions, organic
compounds formed the building blocks of cells
Early History of Earth
• Scientists suggest
early Earth was very
hot
• About 4.4 billion years
ago, Earth might have
cooled enough for the
water in its
atmosphere to
condense
The Origin of Life – Modern
Ideas
• In 1953, Stanley Miller and Harold Urey stated
that original life on Earth developed in the
oceans from simple organic molecules
– In the oceans were molecules such as hydrogen,
methane, and ammonia gases that started to react
due to a spark of energy (lightning)
– Eventually, organic compounds such as amino acids
and sugars formed
• Conducted an experiment that actually formed
organic molecules
Figure 4.2
EXPERIMENT
“Atmosphere”
CH4
Water vapor
Electrode
Condenser
Cooled “rain”
containing
organic
molecules
H2O
“sea”
Sample for chemical analysis
Cold
water
Heterotroph Hypothesis
Heterotroph Hypothesis
The Evolution of Cells
• Fossils indicate that by 3.4 billion years
ago, photosynthetic prokaryotic cells
existed on Earth which would supply
oxygen for a developing planet
• Believed that prior to these cells,
anaerobic prokaryotes existed due to
the lack of oxygen
– these would have been heterotrophic,
using organic molecules abundant in
Earth’s early oceans as food
Archaebacteria
• The first autotrophs
appear to be similar
to the archaebacteria
alive today
• These bacteria live in
harsh environments
such as deep-sea
vents and hot springs
The Endosymbiont Theory
• Complex eukaryotic cells probably evolved from
prokaryotic cells
– Mitochondria are similar to ancient heterotrophic
bacteria
– Chloroplast are similar to ancient autotrophic bacteria
Endosymbiosis
Figure 28.4 A model of the origin of eukaryotes
Review
1. How can fossils be used to study ancient
life on Earth?
2. How is radiometric dating used?
3. Describe the contributions of Redi and
Pasteur.
4. Describe Miller’s experiment.
5. Explain the endosymbiont theory.
End Evolution Day #2