The Necessity of Ambiguity

And other characteristics of Geologic Reasoning

Kip Ault

Science methods match the demands characteristic of problems

--S. Toulmin, 1990, Cosmopolis

"Interpretation" is a characteristic demand of geologic problem-solving.

Darwin's work established the basis for the "historical style" of science, different from the "experimental style."

--Stephen Jay Gould, 1986 "Evolution and the Triumph of Homology"

Delta or estuaryat the mouth of a great river?

""

Ambiguity in conceptsabout the continental margin

• An atom of Carbon-12 is an element without a history. All members of the category are the same.

• Understandings of continental margins demand comparisons. All members of the category resemble and differ from each other due to their histories.

• Reasoning in the style of "compare and contrast" requires ambiguous categories.

Ways of constraining the ambiguity of geologic concepts:

The example of a submarine “fan”

• Metaphorically, “sea- floors” have “fans.”

• Comparatively, fans share processes of fan formation.

• Comparatively, fans resemble other fans, yet are distinct from deltas and canyons.

• By contrast, boundaries among fans, deltas, and canyons reveal the most interesting of conditions: a “fan complex.”

• Descriptions of how “fan complexes” resemble and differ from each other serves explanatory purpose.

The puzzle of Neahkahnie Mountain, northern Oregon coast. Once lava filled asubmarine canyon and turned to stone.Now these rocks stand in high relief above the surf.

Why?

The historical style of science• Uniformitarianism across scales: Darwin’s

worms.

• Place substitutes for time: Pacific atolls.

• Infer history from its results through comparing and contrasting: Oregon Cascades

• Categories of description carry inferences: granite rock.

• Members of categories differ due to their histories: river deltas and seafloor fans.

Historical strategy: “place substitutes for time”1. Claim by Darwin: Lagoons form from sinking atolls, enclosed

by growing coral reefs.

2. Concepts linked to methods: Consider present time as a sampling distribution of landscape changes over vast time among atolls, fringing reefs, volcanic processes.

3. Problem-solving strategy: Presume that present time samples stages. Attempt to arrange them in order.

4. Validate with an independent chronology.

5. To understand how landscapes change, find structures representative of different stages. In the Cascade Range, one volcano may suggest Mt. Hood’s past and another its future.

The concept of criterion of excellence

1. A claim is made in the context of an inquiry.

2. The claim links categories of description with methods of investigation.

3. This linkage evolves into a strategy for solving particular problems.

4. Investigators evaluate new claims in light of this strategy.

Criteria of excellence for the historical style of science:

• Place substituting for time

• Integration across scales

• Adequate geographic and temporal sampling

• Independent chronology for sequence and simultaneity.

• Constrain ambiguity (e.g., fans and deltas)

An example of the criterion of integration across scales

• Cretaceous-Tertiary boundary and the anomalous iridium-rich layer

• Global extinctions; end of the Age of Reptiles

• Shocked quartz and its geographic distribution

• Chixulub Crater and its age

In order to learn meaningfully be careful to study:

• How the conceptualization of the phenomenon of interest interacts with the methods of its investigation.

• How this interaction achieves explanatory ideals.

• How the results of investigation call for the invention of new concepts.

For example:Fundamental geologic concepts: faults, deltas, volcanoes, mantle plumes, plates—include objects that differ from each other due to unique histories.

In contrast, members of chemical categories—elements, isotopes, compounds—have the same properties.

The ambiguity of concept boundary is a necessary feature of geologic reasoning. The certainty of concept boundary is a necessary feature of chemical reasoning.

Each member of a geologic category has a history. The objects of interest extend across scales in time and space. Problems differ from one scale to another.Controlled experimentation plays a limited role.

Each science responds to a challenge.The characteristics of challenges differ:scale in geology, human diversity in medicine.Diverse responses, conceptually and methodologically, are therefore needed, for example, in geology:

• Use analogies to compare and contrast• Integrate solutions across scales

Summary:

Conclusion:

Geology is not physics; nor entomology, nor anthropology, nor biochemistry, nor . . . science reduced to universal processes.

Thinking and doing adapt to the nature of the challenge.

"On the conception, all else depends.“

--Joseph Schwab, 1962, “The Concept ofthe Structure of a Discipline”