Geo 105: Lect 1, Jan. 8
- Before discussing Plate Tectonics, the great revolution in Earth Sciences,
we must try to define Earth Sceinces...
and thus ponder what is science?
- Since the Earth is made of matter, has processes that follow
the Laws of Physics, and interacts with life, Earth Sciences
encompasses Physics, Chemistry, and Biology.
- It is a "Natural Science"
- My view of Natural Science is that the object of interest
is surrounded by a loose confederation of observations & hypotheses.
The classic view of experimental science is just one aspect of the
natural scientific process.
- My conclusion: science is a natural human activity, practiced by all people.
- "Occam's Razor" is a key belief in the natural sciences:
"The simplest explanation that explains the observations is
the best explanation."
- What are some of the most basic questions & features of the Earth?
- How to explain these features?
- The KEY question is "how old is the Earth?".
- To the extent that they could measure time, most people thought
the Earth is young.
- Since many geologic features, e.g. Mountains, are not made in our lifetime,
people are forced to propose that Mountains were formed by
incredible processes that are not occurring today.
If true, we can not say very much about how anything was made.
- But, geologists began to think that the Earth was old.
- The Uniformitarian Principle (proposed by James Hutton in 1785,
popularized by Charles Lyell in 1830).
Briefly stated: "The present is the key to the past."
Longer description: "Rocks formed long ago at the Earth's surface
can be understood and explained in accordance with physical processes now operating" (J. Gilluly, 1951).
- One implication: Mountains are being made today, but the process is so slow we do not easily recognize it.
- Discovery of fossils (key person & date, William Smith. 1793), eventually giving rise to the notion
that organisms can slowly change over time.(in particular, "On the Origin of the Species by Means of Natural Selection", C. Darwin, 1859.
- Implication: the Earth is old, very old!
- Today, we know that the Earth is about 4.5 billion years old.
It is difficult to fathom such huge exapnses of time.
...Click for a Geologic Time Scale (with major extinctions)
