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Unraveling Geological Time

Anchisaurus locality, Nova Scotia
Anchisaurus
Outcrop in Nova Scotia, Canada of the McCoy Brook Formation of Early Jurassic age in which a dinosaur skeleton was found (box) 
Reconstruction by O. C. Marsh of type of dinosaur (Anchisaurus sp.) found on left. 

I. You find a dinosaur: How do you know how it got there, its age, and relation in time to any thing else?

You could make up stories.
But how to decide which is right?
First, we all agree that we are going to make a scientific study. What does that mean?
In Science we make up explanatory stories and try to make generalizations.
SCIENCE IS BASICALLY A CONVERSATION WITH NATURE
Science differs from all other human activities in that there is an external source of judgment:
* Correspondence to reality
* Scientific hypotheses have TESTABILITY.
Differs from religion because precepts can be changed and must be at least potentially subject to external judgment. Differs from art because we agree there is only one explanation, one valid interpretation.
Judith and Holofernes
 
Consider a painting (in this case by
Artemisia Gentileschi) of Judith slaying Holofernes (1597?-after 1651)
Many equally valid interpretations are possible of this painting - and you may feel many equally valid emotions.
Literary criticism, Poetry, and Music interpretation, are similar.
Law - Rule of conduct and persuasion, no necessary correspondence to reality.
So what makes science different is that it is constantly tested against correspondence to reality.
Of course, motivation of participants is complex and may have little to do with results of science.

II. Now in the case of our little dinosaur, we can't start at the beginning - we go into a large body of shared knowledge - i.e. lots of hypotheses which have stood up over many tests - HELPS US TO EXTEND OUR PERCEPTION

What does this body consist of in Geology and Paleontology that helps us along?
 
 
 
The Grand Canyon 
Grand Canyon Image
There are three basic fields: * STRATIGRAPHY 

* BIOSTRATIGRAPHY

* GEOCHRONOLOGY 


 
These principles go back to the 17th century.

III. Most important is the Dane Nils Stensen - AKA ? Nicolaus Steno: 1638-1686

He wrote the first real geological treatise while living in Tuscany, Italy:
"The head of a shark dissected"
Glossopetrae or "tongue stones" were found scattered along some layers in the mountains around Tuscany. They were in fact found imbedded within stone. Steno did a detailed description of a sharks head and reasoned that the Glossopetrae were in fact the teeth of sharks that had lived when the mountains were under water.
This lead him to his second work which was of great power, and dealt with the question of how did a solid body (such as the sharks tooth) get within another solid body (i.e. rock)?
This second work was:
"The prodromus of Nicolaus Steno's dissertation concerning a solid body enclosed by a process of nature within a solid"
THIS WORK WAS THE FOUNDATION OF OUR UNDERSTANDING OF READING THE ROCK RECORD
Steno postulated 4 principles of stratigraphy
* 1. Principle of superposition of strata
* 2. Principle of initial horizontality of strata
* 3. Principle of stratal continuity
* 4. Principle of cross cutting relationships
ALL ABOUT INFERRING TIME FROM GEOMETRY
This seems to have had a big effect in a number of places, especially France and Great Britain where the next major advances were made.

IV. Antoine-Laurent Lavoisier

Lavoisier was to become the greatest chemist of the 18th century, but before this, while his chemical interests were still growing, he worked with Jean-Etienne Guettard, a geologist mapping of the geology of France. Gould (1998), has recently pointed out that Lavoisier deduced the vertical succession of rock strata from the map distribution of rock-types and hence translated geometry of the present into a past sequence of events, represented by the succession of rock strata. 

map

Lavoisier

Marie-Anne Pierrette Paulze (1758-1836) and Antoine-Laurent Lavoisier (1743-1794). Paulze married Lavoisier at 14. Lavoisier was beheaded in 1794 after the French Revolution; Paulze later married the American physicist Benjamin Thompson (Count Rumford) and they published Lavoisier's Memoires des chemie.

V. James Hutton

Scottish - Changed careers three times and didn't publish until he was 62.
Lived from 1726-1797: during a time when natural phenomena were being explained by natural causes.
Observed unconformities, and believed in cycles.
Proposed the Rock Cycle
EXPLAINED EARTH'S NATURAL PHENOMENA BY NATURAL CAUSES WHICH HE COULD SEE OPERATING TODAY
Led to what we call:
THE PRINCIPLE OF UNIFORMITARIANISM - REVELED IN THE CONCEPT OF DEEP TIME
He viewed the Earth and Earth history as having, "no vestige of a beginning, no prospect of an end."

VI. William Smith 1769-1839

Age of canal building - Smith was a canal engineer.
Discovered that different rock formations contain distinct fossil assemblages and that even isolated areas of rocks could be identified in their sequence by the fossils they contained.
Made a map of England published in 1814-1815
Strata identified by organized fossils 1816-1819
* Principle of Biotic Succession
Allowed rocks in disparate areas to be ordered.
20 years of intense work by geologists in Europe and North America ordered rock sequences and resulted in the naming of most "time periods".

VII. Principles, evidence, and results brilliantly summarized by Charles Lyell (1797-1875) in "Principles of Geology" 1830; went through 11 editions.

Lyell's Principles of Geology
Lyell was a very strong uniformitarian and felt that that to large measure, not only had the kinds of natural processes not changed, but also that the magnitude of processes had not changed.

The Earth must therefore be very old.

All the big changes in Earth History were all due to the sum of small effects over very long time periods.

Charles Lyell
First edition of "The Principles", 1830. (N.G. McDonald Collection)

Sir Charles Lyell
(N.G. McDonald Collection)


The full title, quite revealing, of Lyell's tome is, "Principles of Geology, being an attempt to explain the former changes of the Earth's surface by reference to causes now in operation". The frontispiece (left) shows the temple of Serapis at Puzzuoili, Italy as it appeared in the early 19th century. The  pillars are covered by several generations of marine animal encrustations (visible as different bands) showing that since its construction there had to be multiple episodes of vertical movement at the scale of several meters, alternately submerging and exposing the pillars to different levels.

Lyell quoted Playfair, popularizer of Hutton on the title page of his 1847 edition; "Amid all the revolutions of the globe, the economy of Nature has been uniform, and her laws are the only things that have resisted the general movement. The rivers and the rocks, the seas and the continents, have changed in all their parts; but the laws which direct those changes, and the rules to which they are subject, have remained invariably the same".

VIII. Charles Darwin (1811-1882)

Applied Lyellian Uniformitarianism to organisms.
Insensibly graded series - evolution by natural selection.
Origin of species - 1859.
VAST AMOUNTS OF TIME NEEDED.
EXPLAINED WHY PRINCIPLE OF BIOTIC SUCCESSION WORKS.
* WE NOW BASICALLY USE SIMILARITY IN THE FOSSIL ASSEMBLAGES TO INFER PROXIMITY IN TIME.
Not the kinds of fossils present (e.g. shells vs. teeth, but rather the specific species of plants or animals present.
For example: Ammonites - restricted to Late Paleozoic and Mesozoic.
One particular species (Psiloceras planorbis) is known only from rocks of early Jurassic age.
* CONSTANT TESTING AND RETESTING OF CONSISTENCY
* ALONG WITH STENO'S PRINCIPLES OF STRATIGRAPHY, THIS HAS ALLOWED THE RELATIVE ORDER TO BE ESTABLISHED

IX. BUT HOW TO MEASURE GEOLOGICAL TIME IN YEARS?

* You could use sedimentation rates:
Determine the amount of sediment being delivered to the sea by rivers. Calculate how this one year's worth of sediment would be spread over the ocean floors and use that rate (thickness of 1 year's sediment / 1 year). Then use this to convert the thickness of rock strata from thickness to years.
[ thickness / ((thickness of 1 year's sediment) / 1 year)) ]
What do you think some of the problems with this would be? (e-mail me some answers!)
* You could do a similar calculation with the saltiness of the ocean. (e-mail me some suggestion on how to do this!)

X. William Thomson (Lord Kelvin) - 1824-1880's

Sun is hot now, how long will it remain so:
1855 - 20-25 my for the right temperature for organisms to exist.
Also similar estimates for age of Earth from cooling from a molten ball.
Most geologists and especially paleontologists suffer from "physics envy" and are susceptible to bludgeoning by math and physics wielded by a strong physicist such as Kelvin.
In Kelvin's 1868 address on geological time he did just that and kept a lot of geologists from following the idea that the Earth was very very ancient.

XI. But in 1899, the geologist T. C. Chamberlain gave an address in which he said,

"Is present knowledge relevant to the behavior of matter under such extraordinary conditions as obtain in the interior of the sun sufficiently exhaustive to warrant the assertion that no unrecognized sources of heat reside there? What the internal composition of the atoms may be is as yet an open question. Is it not improbable that they are complex organizations and the seats of enormous energies? ...No cautious chemist would probably venture to assert that the component atomecules, to use a convenient phrase, may not have the energies of rotation, revolution, position and be otherwise comparable to those of a planetary system. Nor would he probably be prepared to affirm or deny that the extraordinary conditions which reside in the center of the sun may not set free a portion of this energy."

XII. THE KEY TO MEASURING GEOLOGICAL TIME IN YEARS TURNED OUT TO BE RADIOMETRIC DATING OF ROCKS AND MINERALS

Basic Chronology:
1896 - Henri Becquerel discovers radioactivity - acts like x-rays discovered by Röntgen and darkens photographic plate.
1902 - Ernest Rutherford and Fredrick Soddy framed atomic disintegration theory:
"the atoms of radioactive bodies are unstable and a certain fixed proportion of them become unstable every second and break up with explosive violence, accompanied in general by the expulsion of an alpha- or beta-particle. The residue of the atom, in consequence the loss of an a-particle, is lighter than before and becomes the atom of a new substance quite distinct in chemical and physical properties from its parent."
(alpha-particles are helium atoms and beta-particles are electrons)
1904 - Rutherford described how heat of Earth and Sun could be accounted for by radioactive decay
1905 - Bertram Boltwood, Yale, U-Pb, and John William Strutt (with Ra-He) dated various "old rocks and got ages of 400 to 2000 million years".
1911- 1927 - Arthur Holmes, U-Pb, U-He methods produced the first calibrated geological time scale.
From then to now, many thousands of dates by many methods.

XIII. RADIOMETRIC DATING OR ROCKS AND MINERALS - overall statement

I. The basic principles of radiometric dating as worked out by Rutherford in about 1902 are as follows:
1. When a crystal of a mineral forms it starts with some amount of a radioactive element.
2. As the "parent" radioactive element decays, the "daughter" element stays locked within the crystal.
3. No "extra" of the daughter-type element can be present.
4. The decay rates of the element must be known.
5. Then the ratio of daughter to parent can be used to calculate the age of the formation of the crystal.
* Should be no confusion: radiometric dating works on the same principles as nuclear weapons and is based on the same basic theory - contra creationists

XIV. This has allowed fantastically detailed knowledge about the past both in terms of relative order and in terms of absolute time.

Lets look at the time scale as it stands now.

I know its difficult to remember, but here are some acronyms that will help you.

NOW LETS LOOK AT OUR DINOSAUR AGAIN:

Anchisaurus locality, Nova Scotia Drawing of Anchisaurus locality, Nova Scotia
Outcrop in Nova Scotia, Canada of the McCoy Brook Formation of Early Jurassic age in which a dinosaur skeleton was found (inset box)  Drawing of the outcrop on left, emphasizing layering. 
Letters on right are: a, brown, wind blow sand; b, layering demarkated by the boundaries of thin lava flows (basalt); c, angular blocks of basalt with a matrix of brown sandstone (a fossil talus slope deposit).

First we look at the rocks:

Layering in sandstone (a) tilted - must have been more extensive. Lava flow (b) all busted up and abutting sandstone which drapes over it. Sandstone must be younger than basalt.
PRINCIPLE OF STRATAL CONTINUITY
PRINCIPLE OF ORIGINAL HORIZONTALITY
PRINCIPLE OF UNIFORMITARIANISM
What was the environment that produced the sandstone?
Dinosaur in sands which look like dune sands, in detail - probably are fossil dunes produced in a desert.
What is the rubbly rock that looks like it is made of basalt boulders and sandstone (c)?
Sands contain blocks of basalt arranged as talus cones - probably are fossil talus cones.
PRINCIPLE OF UNIFORMITARIANISM
What of the animal itself?
Turns out to be a prosauropod dinosaur, probably Anchisaurus - known elsewhere in the world only in rocks of Late Triassic and Early Jurassic age of the Mesozoic -
PRINCIPLE OF BIOTIC SUCCESSION
What is found nearby associated with the lava flow?

Red Head, Nova Scotia

Lava flow (brown and gray - North Mountain Basalt)

above Triassic and earliest Jurassic age strata, Five Islands Provincial Park, Nova Scotia.

In the lava flow itself:
Using the 40K-40AR decay scheme the age of the lava flow is about 200,000,000 years old - consistent with ages throughout to be around the Triassic-Jurassic boundary (193-213 million years ago)
APPLICATION OF RADIOMETRIC DATING
Just below that is a gray layer containing the fossil pollen of plants:
Compares well with the pollen in marine rocks in England and Germany in rocks which contain many marine fossils (including Psiloceras planorbis) correlating with the Early Jurassic in the Jura mountains
PRINCIPLE OF BIOTIC SUCCESSION
Below that are other gray layers with pollen of rather different composition comparable to what is found in the prosauropod beds themselves in the type Triassic age rocks in Germany.
PRINCIPLE OF BIOTIC SUCCESSION
Thus, we would conclude that the rocks deposited around the prosauropod bones are younger than the lava flow and the Triassic-Jurassic transition -
PRINCIPLE OF SUPERPOSITION
WE MIGHT MAKE OTHER PREDICTIONS OF WHAT WE SHOULD FIND: OTHER REPTILES, NO TRIASSIC TYPES, OTHER RADIOMETRIC SYSTEMS AGREEING ETC.
Test, TEST AGAIN, adjust.

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