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U4735x Environmental Science for Decision Makers

Problem Set #1: Earth and Life Timescales.

9/4/03, due 9/11/03 at class time.

Use data from the accompanying table to answer the first seven questions. In each case, all that is required is to divide one number by another, keeping track of the powers of 10. The purpose of these questions is to become familiar with scientific notation and very simple order-of-magnitude calculations. The following seven questions are related to the first seven, and are intended to explore a few basic scientific ideas. Prose answers should be VERY brief, indicating the logic of your answer. Each question assigned a total of 5 points: total 70 points.

  1. For what portion (percentage) of Earth history has the atmosphere contained appreciable free oxygen ([O2] > 1%)?

  2. For what portion (percentage) of Earth history has single cell (prokaryotic) life been present?

  3. For what portion (percentage) of Earth history have multi-celled marine organisms left fossil shell remains?

  4. For what portion (percentage) of Earth history have Homo sapiens (modern humans) existed?

  5. What portion (percentage) of the time since irrigated agriculture was developed in the Middle East does the modern era of large-scale petroleum combustion represent?

  6. If the average duration of a glacial-interglacial cycle has been 1 x 105 years, approximately how many such cycles have occurred since Pleistocene glaciation began?

  7. If global river discharge and ocean volume had been the same since the first geological evidence of the presence of an ocean as they are today, how many times has ocean water been completely recycled through river discharge from the land to the sea over the entire period of Earth history since there was first an ocean?

  8. Do you think explicit public policies are currently needed to preserve oxygen levels of the atmosphere? Why or why not?

  9. Do you think primitive (prokaryotic) types of single cell organisms still exist on the Earth? Are they abundant? Are public policies needed to protect them?

  10. What is the formal name for the Geological Period in which marine fossil shells first appeared in abundance?

  11. Did early Homo sapiens probably encounter dinosaurs during their search for food? Why or why not?

  12. Given the very long human experience with irrigated agriculture, is it reasonable to describe our current irrigation practices as "sustainable"?

  13. Do you think the evolution of Homo sapiens and earlier human species was influenced significantly by the extreme climate fluctuations of the last 2 million years?

  14. If rivers have been eroding land surfaces and transporting sediments to the oceans for the last 4 billion years, why have the continents not been completely eroded down to sea level?
Earth and Life Time-Scales: Examples
YEARS*
EVENT
3 x 10-2 Atmospheric H2O vapor recycling time.
4 x 10-1      One semester course.
4 x 100 El Niño repeat time (average).
5 x 101      Siltation of Indus River reservoir.
1 x 102      Petroleum combustion era begins.
1 x 104      Early irrigation agriculture in Middle East.
2 x 104 Maximum cold of latest glacial episode.
4 x 104 Time to supply ocean H2O volume from global rivers.
2 x 105      Homo sapiens (modern humans) evolve; use of fire.
2 x 106 Pleistocene glacial cycles begin.
1 x 108 Time to supply ocean dissolved NaCl from global rivers.
6 x 108      Oldest marine fossil shells.
2 x 109      Appreciable O2 (> 1% of present level) in the atmosphere.
4 x 109      Early life (prokaryotic single cells).
4 x 109 Evidence of an early ocean.
5 x 109 Age of the Earth.
* Scientific notation form (powers of ten): A x 10b