Can we use the scientific method, when investigating past events in Earth's history, in order to determine their cause(s)? In other words, is it possible to suggest a cause for an ice age, or the extinction of group of animals, and test whether or not for this hypothesis is plausible and others can be eliminated?
In many cases, an original hypothesis typically generates many follow-up studies, some of which support and others which invalidate the proposed cause or process or which reveal some flaws in the hypothesis. Sometimes, an improved understanding of a process forces us to re-evaluate earlier hypotheses that were plausible when they were first proposed.
To give you some insight in this type of research, here are the steps in the preparation of your term paper:
A topic (which you cannot
choose) but which would fit the objectives listed above is the scientific
determination of the absolute age of the Earth. A student choosing this
topic could include the following elements in the term paper:
- the event chosen: the
formation of the Earth, a very long time ago.
- evidence for this statement:
thickness of sedimentary rocks found in many places on Earth.
- the nature of the hypothesis
proposed by Lord Kelvin: the Earth formed 20-40 millions of years ago (p.
164 in textbook)
- this age could be calculated
from current heat flow (measurable process taking place today) if the source
of the heat was only cooling of magma that formed the Earth
- evidence cited by Kelvin
which supported his hypothesis:
igneous rock formed
from magma, measurable heat flow increases with depth, cooling of deep
magma still continues to this day
- the only test that Kelvin
could propose were heat flow measurements across the planet and at various
depths within the Earth's crust because he didn't suspect that any other
process could account for this internal heat
- follow-up studies invalidated
his hypothesis by determining much older absolute ages for some of Earth's
rocks by the analysis of radioactive element-radiogenic daughter element
in minerals from igneous rocks
- Kelvin's hypothesis was
therefore tested by the radiometric dating of rocks
- conclusions:
- the
Earth's crust contains significant quantities of these radioactive elements
- this
natural radioactive decay releases a considerable amount of energy as heat
- conclusion:
the cooling rate of the Earth is considerably slower than if it had no
natural radioactivity.
- In this case, a plausible
scientific hypothesis was presented, but it was eventually tested by a
method that Kelvin could not have predicted. The later discovery and understanding
of radioactive decay provided a tool for absolute dating of igneous rocks,
and explained why Kelvin's estimate of the Earth's age was too low.
Another topic, which blends biology and physical geology, might be the origin of the banded iron formations. They formed in abundance only in Precambrian times. One hypothesis is that they represent chemical sinks which slowed down the rise of oxygen produced by photosynthetic prokaryotes in the atmosphere. The hypothesis is still being tested by scientists studying other indicators of the presence of atmospheric oxygen, and scientists studying other types of anaerobic bacteria. You might discover a study suggesting that bacteria that do not photosynthesize could have produced the BIFs in an oxygen-poor ocean. Your conclusion might be that this remains an open question if there are several plausible mechanisms for producing BIFs.
Your outline is a fairly complete "plan" of your term paper, intended to make sure that you are on the right track. It must spell out the content of your term paper in point form or in complete sentences.
- what is the event chosen
(when did it occur and where?... was it worldwide or restricted to an area?)
- what is the nature of
the evidence (rocks, fossils, sediments, water chemistry) for the event?
- what hypothesis presented
for the cause of the event will you discuss in your term paper?
- which 1st study (primary
or secondary literature) presents evidence for the event and a possible
cause?
- how can the hypothesis
for the cause of the event be tested: does the hypothesis predict the type
of evidence that can then be sought, and where it should be found?
- what is the 2nd study
(primary or secondary literature) that tests the hypothesis?
- what new evidence does
the second study provide (more of same type, or a new type of evidence)?
- a short bibliography where
you indicate your sources of information found so far: label these sources
as primary literature (articles presenting evidence collected and analyzed
by the authors), secondary (evidence is discussed but it was collected
by others, whose work is referenced) or tertiary literature (no direct
reference to primary sources of information but an interesting overview
of the topic).
Grading criteria of final term paper (represents 20% of your total grade in this course):
20% clarity of presentation
of the event and evidence for it (e.g., data supporting its occurrence
& timing).
20% clarity of presentation
of the hypothesis.
20% clarity of presentation
of the test of the hypothesis.
15% quality of language:
spelling, syntax, proper use of terms.
10% quality of your evaluation
of how well the studies illustrates the scientific method.
10% bibliography: proper
citation style, at least 2 primary/secondary literature sources.
5% for addressing
comments made by T.A. on the original outline (0% if no outline is submitted).