Earth Evolution and Life History

1
Earth Evolution and Life History

• Dr. Michael Harrison
• Spring, 2009

2
What is Geobiology?

• Study of interactions between the biosphere and
  the geosphereinvolves the hydrosphere,
  atmosphere, lithosphere, and cryosphere

Tree of Life (based on genetics)
3
What is Geobiology?

• Origins and evolution of life
• Evolution of atmosphere, hydrosphere,
  lithosphere, and biosphere
• Evolutionary ecology and microbiology
• Biogeochemical cycles (e.g., C, S, P, N)
• Microbe-rock/mineral interactions
• Biomarkers (organic molecular fossilse.g.,
  lipids, kerogen, isotopes)
• Astrobiology (life on Mars methanogens on Titan?)

Evidence of flowing liquid methane on Titan
4
Why Study Geobiology?

• 99 of all species that ever existed on Earth
  are now extinct need fossils to study past life
  and give context to living species today also,
  estimated 3-200 species/day committed to
  extinction
• Earths characteristics (e.g., composition,
  temperature) and processes (e.g., plate
  tectonics) directed the formation and evolution
  of life
• Many geologic processes involve life processes
  (e.g., lithification, weathering, mineral
  precipitation, ore formation, petroleum)
• Appreciate the linkages between the biosphere and
  geosphere for instance, without the evolution of
  photosynthesizing cyanobacteria 3 billion years
  ago, Earths atmosphere would be largely devoid
  of oxygen

5
What is Science?

• Particular way of understanding the natural,
  physical world (no supernatural phenomena)
• Connects past, present, and future
• Differs from theology and philosophy. How?

Einstein
Descartes
St. Thomas Aquinas
6
Methods of Science

• Requires observations (direct and indirect) and
  physical evidence. Must obey rules
• Explanations (hypotheses) must be tested
  rigorously. Tests (experiments) confirm or
  reject hypotheses. A theory is more than a
  hunch!
• ALL scientific ideas have the potential to be
  rejected (new info may arise) non-dogmatic

7
Hypotheses

• Hypotheses can be formulated before or after
  observations are made
• Accommodation occurs when hypotheses are
  constructed after observation (hypothesis fits
  the observations)
• Prediction occurs when the hypothesis is
  formulated before observationsthese observations
  then verify validity of hypothesis
• Both accommodation and prediction are acceptable
  methods of constructing hypotheses

8
So, what is a good scientific hypothesis or
theory?

• Robust explanation passes scrutiny (results
  replicated by other scientists)
• Reasoning, peer review, and time cull out weak
  hypotheses
• What about Pseudo-Science? Astrology
  (horoscopes), homeopathy, creation science, and
  much alternative medicine is not truly scientific
  in its methods (e.g., supernatural explanations,
  no peer review, motivated by personal bias or
  beliefs)

9
How to Evaluate Hypotheses

• Does it survive falsification (Popper)?
• -falsification is a rhetorical strategy, not a
  cornerstone of scientific inquiry
• A better measure of reliability for hypotheses
  (1) testability (2) review for errors (3)
  eliminating alternative hypotheses (method of
  multiple-working hypothesese.g., Chamberlin)
• Interestingly, successful predictions do not
  always guarantee correctness (e.g., Ptolemys
  geocentric solar system predicted eclipses and
  position of planets)

10
Characteristics of Science
11
1. Conclusions of science are reliable, though
tentative

• Work in progress (new info may require change)
• Example geocentric vs. heliocentric solar
  system plate tectonics

12
2. Science is not democratic

• Majority do not win! Scientific revolutions
• Example Alfred Wegeners Continental Drift
  hypothesis

13
3. Science is non-dogmatic

• Nothing in the scientific enterprise or
  literature requires belief or faith (sometimes,
  scientists make assumptions).
• Scientists dont believe in an idea scientists
  are convinced by the physical evidence.
• A belief requires no justification (e.g.,
  astrology, alternative medicine, legends, aspects
  of religion)

14
4. Science cannot make moral or aesthetic
decisions

• Philosophy, ethics, religion provide guidance

15
5. Science is not Truth

• Science seeks to establish patterns or
  relationships (cause and effect) between
  observations does not address issues of purpose.
• Useful for prediction and postdiction

Durers Melancholy (1514)
beware of obsessions
16
6. Science corrects itself

• People make mistakes science methods are not
  wrong, scientists are wrong.
• Science is not commentaries, opinion, or
  editorialsits a peer-reviewed process

17
7. Science is a human endeavor

• Bias, preconceptions, pet hypotheses may hinder
  scientific investigation
• Believing is easy, and knowing is hard

Geocentrism ruled 1300 years!