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Impacts on Lithosphere (Land)


4.2.1    Impacts on Lithosphere (Land)

This section examines PAST Impacts of climate change seen by reading the landscape looking for clues of glacial retreats like spillways, old lake levels, spurs and layers in valley walls, and plunge pools.

Try the virtual tour of the Niagara Escarpment as a detective!!

Geological Time Scale













The time scale is depicted in its traditional form with oldest at the bottom and youngest at the top – the present day is at the zero mark. Geologic time is finely subdivided through most of the Phanerozoic but most of the finer subdivisions (e.g., epochs) are commonly referred to by non-specialists only in the Tertiary.

Relative time or chronostratic – physical subdivisions of the Earth’s geology (rock in stratigraphy) in a specific order based upon relative age relationships and are given names usually on the basis of fossils.

Absolute time or chronometric – numerical ages (actual time) in millions of years before present (mbp) obtained by radiometric dating rocks.

Every dated boundary has an uncertainty associated with it, expressed as + or – X millions of years. None of the values depicted should be considered definitive as they are continually being refined. The overall duration and relative length of these large geologic intervals is unlikely to change much, but the precise numbers may wiggle a bit as a result of new data.


  • Name the two Eons.What are the name of the chronometric Eras found in the Pre-Cambrian?
  • What event happened 4 500 mbp?
  • What era, period, and epoch are we in today?
  • When didi the pre-Cambrian Era end?
  • Which is the longer eon? What time span?
  • What is the longest era? Shortest? Time span?



Blatt, H.; Berry, W.B.N.; and Brande, S., 1991. Principles of Stratigraphic Analysis. Blackwell Scientific Publications: Boston, p.1-512. ISBN 0-86542-069-6 [Chapter 4 provides an introduction to geologic time. This is a good starting point to get the basic principles.]

Grotzinger, J.P.; Bowring, S.A.; Saylor, B.Z.; and Kaufman, A.J., 1995 (Oct.27). Biostratigraphic and geochronologic constraints on early animal evolution. Science, v.270, p.598-604. [The most recent revision of the age of the Precambrian/Cambrian boundary.]

Harland, W.B.; Armstrong, R.L.; Cox, A.V.; Craig, L.E.; Smith, A.G.; and Smith, D.G., 1990. A geologic time scale, 1989 edition. Cambridge University Press: Cambridge, p.1-263. ISBN 0-521-38765-5 [One of the more recent compilations of the entire geologic time scale.]

Holmes, A., 1937. The Age of the Earth (new edition, revised). Nelson:London, p.1-263. [One of the earlier attempts at an integrated geochronologic time scale.]

Obradovich, J.D., 1993. A Cretaceous time scale. IN: Caldwell, W.G.E. and Kauffman, E.G. (eds.), Evolution of the Western Interior Basin. Geological Association of Canada, Special Paper 39, p.379-396. [Proposes revisions to the Cretaceous time scale at the resolution of stages (finer divisions than shown on diagram above) and sub-stages.]

Authorship and distribution
(c) 1996 macrae@geo.ucalgary.ca
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