Study Questions

 Guide #9 (F04)

 GEOL 125: Earth History

 Dr. Hammond

What are excess volatiles, and what are their possible sources? What are the likely sources of the water and salt needed to form oceans? What are the principal gases in the atmosphere today? What are the likely sources of each gas?

What evidence indicates oxygen concentration in the earth's atmosphere has changed through time? Why might this occur? Write a chemical reaction to illustrate photosynthesis and explain how this could modify the atmosphere. What is the ozone layer and why does it exist? Why is it important to us and other life forms?

What is the meaning of steady state in a dynamic system? What types of feedbacks exist and what do role do feedbacks play? What negative feedbacks act to regulate atmospheric oxygen? Draw a graph illustrating the effects of feedbacks that relate input and loss to O2 concentration.

Where are the oldest rocks in the North American craton? Why are relatively young rocks generally found on the edges of continents? How have the oceanic and continental crust formed? Has the volume of continental crust increased, decreased, or remained the same during the earth's history?

What differences exist between the oceanic and continental crust in composition and density? If oceanic crust has a higher density, why doesn't continental crust lie on top of it? Draw a diagram to show why water overlies the oceanic crust and not the continental crust.

What are possible sources of energy to heat the early earth? Draw a graph illustrating the change in heat produced by radioactive decay in the earth vs. time since the earth formed. The interior of the early earth was much hotter than at present. How might this influence plate tectonics, formation of the continental crust, and degassing of the mantle?

Why is the earth differentiated into core, mantle and crust? How do we know the earth has these internal layers? When did differentiation take place, and how have we established this timing?

What super-continents have existed in the past? Why do we expect super-continents to break up? What linkages exist between global sea level and plate motions? Why? How can we recognize transgressive-regressive sequences that can be used to determine past sea level?

What is deterministic behavior? What is chaos? What provides stability in dynamic systems?

How and when did the moon form? How old are the oldest rocks on Earth? When did life originate? How do we know the timing of these events? What major transitions can be recognized in the fossil record that are defining points in the history of life? Draw a time line and indicate the geologic ages of these events.

Terms to know

 biogeochemical cycle  238U, 235U, 40K, 40Ar
 detrital pyrite  banded iron formations  red beds
 photosynthesis  degassing  volatile
photodissociation  respiration  komatiite
 accreted terrane  continental craton  
 orogeny  partial melting  negative feedback
 Laurentia  Appalachians steady state
 Rodinia  Gondwanaland  positive feedback
 Pangea  Miller  Urey