Humboldt State University ® Department of Chemistry

Richard A. Paselk

Science 331
Fall 2004 Lecture/Activity Office: SA560a
Notes: 29 November Phone: x 5719
Home: 822-1116
e-mail: rap1

Deep Time and The History of the Earth

How do we know ages?


  1. Stellar Life Cycle: Stars burn hydrogen at particular rates depending on how big (bright) they are. Oldest globular clusters have only stars dimmer than the Sun (< 0.7 solar mass) implying ages between 11 By and 18 By (Sun will run out of hydrogen and become a Red Giant at about 10 By).
  2. Hubble Constant: Universe is "expanding." That is all galaxies are going away. If calculate how long it has been since they were in same place, then Universe 12-14 By old by recent calculations (range broader in past, narrowed by increasing quality of measurements).
  3. WMAP Satellite: Measures of microwave background pattern, etc. Complex calculations give an age of 13.7 By ±1%.

Earth and Solar System

  1. Rock layers. Layers in sedimentary rock generally will be seasonal, like tree rings. Again can extend range by looking for overlaps. Determined Earth must be 100's of millions of years old in nineteenth century. (Rock thicknesses for various eras tend to be km to miles thick.)
  2. Glacial Ice. Count layers, like in tree rings (below). In very deep ice-fields (Greenland and Antarctica) have gone back over 200,000 years. Includes info on atmosphere etc.
  3. Radiometric dating. Depends on rate of decay of radioisotopes.


  1. Tree rings. Note that can go past oldest living tree if older wood which overlaps is available (e.g. in old buildings, preserved in bogs, at archeological sites). Limited to about 10,000 y so far.
  2. Radiometric dating. Depends on rate of decay of radioisotopes.

Overview of Earth History

The Solar system is almost exactly one-third of the age of the Universe! (4.57 By vs. 13.7 By)

Time line of early Earth: from origin of solar system (4.57 Ga) to present (5 meter model).

Major occurrences of Precambrian (approx. 90% of Earth history):

Phanerozoic time ­ HSU NHM exhibits website

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© R A Paselk

Last modified 29 November 2004