HISTORY OF STRATIGRAPHY AND THE AGE OF THE EARTH AT
THE END OF 18TH
CENTURY AND 19TH CENTURY
THE USE OF THE HISTORY
OF GEOLOGY TO TEACH PUPILS ABOUT GEOLOGICAL TIME
Abstract
Nobody can fail to be aware of the
worldwide celebrations, which accompanied the start of the year 2000. Why did this date
generate so much interest? Was it because of the Millennium Bug or was it the number 2000?
It seems appropriate to consider 1000 years and how long that really represents in
geological terms. Geology is the only science to deal in time as a currency. It is also
the science which is least taught in school. So it seems appropriate to examine the
history of the geological column – how it was developed, by whom and where and how
the perception of the age of the Earth has changed with the centuries. This introduces
students to the history of spatial and temporal awareness through history and how
scientists have changed their theories with advancing knowledge, travel, fieldwork, and
technological ideas. New ideas have arisen and new terminology.
Introduction
Geology is one of the few sciences to study
the fourth dimension. It is also the science which is least taught in school. Therefore
the lecture starts by looking, literally, at how long geological time is i.e. the age of
the earth. It is difficult to understand the length of time involved and therefore use is
made of everyday analogies. Visual, audio and tactile senses are used to strengthen the
awareness of this difficult concept. Secondly, the geological stratigraphic column is used
to illustrate the history of how scientists debated the age of the earth and how that
relative timescale can be used to put an age on earth materials. This introduces students
to two concepts firstly the history of exploring geological time and secondly how human
perception of nature's time has changed through history, by highlighting that there is a
difference between age and time.
These topics will be further illustrated on the fieldtrip
to the volcano Mount Teide.
Geological Time
There are 2 ways of looking at geological
time - in a relative way and in an absolute way. Members of the audience will be used to
illustrate this.
First interactive
part
This will involve the
audience.
Ask the audience to note
on a piece of paper the oldest thing they own. Summarise this verbally.
Two people who are
obviously different in age, are chosen and then the audience is asked to either write down
why one is older or younger than the other and then to discuss with the person next to
them or to share this with the whole audience. Ask the people first if they mind being
guinea pigs!!
Secondly, ask the
audience to decide how they would actually put figures to the age of the person. If
possible, ask the 2 people how old they are or when they were born. They probably will not
know the hour of their birth. So assume 12.00 - noon. Then ask the audience to work out in
years, days and then hours how old they are. This brings in the concept of scale and
relates directly to the hourglass or the alarm clock ticking. At the end of the lecture,
you will ask the audience to add one to the age they have worked out.
Person 1 = age x 365(days
in a year) + (difference in date in month born from today’s date) x 24 (hours in a
day. You may need to add more if it is not noon.) = a
Person 2 = age x 365 (days
in a year) + (date in month born) x 24 (hours in a day) = b
e.g. David is 25 and born
on the 1st of the month. Today is 8th of the month and it is
12.00. So David is 25 x 365 + 7 days old x 24 for the hours = 219,168 hours old. This
introduces the students to very large numbers but they feel an ownership as they can
relate to it. At the end of the lecture add 1.
During the 19th century,
geologists could only reconstruct a relative time scale. The actual age and duration since
the Earth’s birth in millions remained unknown until the dawn of the 20th
century. Table 1 shows
the main people involved in the story.
RELATIVE TIME
The geological column
The development of the chronostratigraphic
scale or the stratigraphic column is seen by some scientists as one of the most
significant achievements in geology. Its development started during the age of heroism
within geology – end of the 18th century. It fulfills the prime goal in
geology by establishing the global standard for a timescale in which to put earth
materials. Most of the divisions was developed over a period of 50 years in the first part
of the 19th century (See
Fig. 1). Most of the systems were established from the study of the
stratigraphic record in Europe and were initially defined on the lithology or rock types
alone. An example of this is the Triassic divided into 3 parts by Von Alberti in Germany
in 1834. The development of the stratigraphic column was furthered by Murchison who in
1835 defined his Silurian system using fossils as evidence. Perhaps this helped Darwin
further clarify his ideas. However it must be remembered that William Smith, the canal
surveyor, had already published his geological map of Britain in 1815 and he had adopted a
holistic approach based on all observations.
Figura 1
The stratigraphic column is now universally
accepted across the world and the names of the individual time units are shown in Table 2. The one exception to this is the Carboniferous first named in
Britain after the vast coal deposits found. However only the top half of this period
contains coal. The bottom part is composed of marine limestones and in recognition of
this, the USGS in 1953 further subdivided the system into Mississippian and Pennsylvanian.
However this terminology is only widespread in America and not in Europe.
The chronostratigraphic scale is a
summation of all stratigraphical knowledge and as such there is no one cliff or quarry
section on the Earth at which all units are exposed. It forms the basis of all geological
maps and correlation. As it forms such an important part of geological study, the
development of the stratigraphic column through the
eighteenth and nineteenth centuries follows the thinking and expansion of the geological
perspective on the age of the earth.
Within this history of geology lecture this
will be explored in 2 ways.
Firstly, in a relative way by exploring the
idea of comparative time using the 5 main principles employed within stratigraphy.
- Principle of Superposition
- Principle of Uniformitarianism
- Principle of Faunal succession
- Principle of Cross cutting relationships
- Principle of Inclusions.
Second to explore the history of the use of
absolute time within geology
The second area of study will be achieved
using firstly the debate about the age of the earth using Archbishop Ussher’s
calculation and the bible and secondly Lord Kelvin, the discovery of radioactivity and its
application to the above debate by Ernest Rutherford. From here the use and limitations of
half lives in radioactive elements will be explored.
The Principles
The principles of stratigraphy are discussed using the main
scientists involved.
- Principle of superposition
Look at the work of Steno (1638 – 1687)
Steno was born in Copenhagen as Neils
Steensen. He studied medicine and anatomy there and in Paris. He traveled widely and
eventually became the court physician to Grand Duke Ferdinand II in Florence.
His observations were based on a comparison
of modern and fossil shark’s teeth. He worked in the hills around Tuscany and was
able to appreciate that the sediments had been deposited in a primeval ocean.
He described his ideas on the relationships
between strata in De solido intra solidum naturaliter contento dissertationis prodromus
(1669).
"At what time there was formed any
bed, the matter incumbent on it was all fluid and by consequence, when the lowest Bed was
laid, none of the upper Beds was extant.
When any Bed was formed, its inferior
surface, and that of its sides, did answer to the surfaces of the interior Body and of the
Bodies lateral.
….Beds, either perpendicular to the
Horizontal, or inclined to it, have been at another time parallel to the same."
From these observations, we have the Principle of
Superposition, basically what lies on top is the youngest.
Figure
2. What is the youngest deposit in this diagram?
- Principle of uniformitarianism
The work of James Hutton (1726 – 1797)
James Hutton was born in Edinburgh in
Scotland where he studied law and then chemistry and medicine at university, first in
Edinburgh but later in Paris and Leiden. He completed his studies in 1749. James Hutton
never practiced medicine but instead studied improved mixed farming techniques in Norfolk
in England. Here new scientific ideas on farming were developing following enclosure of
the fields. First-hand experience of crop rotation and improved road transport allowed
Hutton to take his ideas back to Berwickshire in Scotland and apply them to land he had
inherited. It was from his time in Norfolk that we can trace Hutton’s interest in
rocks and minerals. His ideas on geology developed and mushroomed after he moved to
Edinburgh but this time spent in Norfolk and Berwickshire is important in his developing
and observing geological structures and sections. He realised that the marine erosion he
saw at work on the coasts of England and Scotland and the intrusion of granite into other
rocks demanded an explanation and that the time taken for these processes to occur must be
longer than the 6000 years accepted at that time as the age of the Earth. Hutton believed
in observation and then theory and explanation. His observations on Isle of Arran in
1787and at Siccar Point (Fig.3.) in 1788, are known
worldwide. He gave us the axiom "The present is the key to the past".
From these observations he developed the
idea of unconformities (as shown in Fig. 3) which represented a vast
amount of time. The processes involved in their formation i.e. deposition, subsequent
uplift, folding and then erosion, subsidence and further deposition, must take time and
Hutton's observations showed him that 6000 years was just not long enough for this to
happen. As he himself says:-
"The purpose of this dissertation is
to form some estimate with regard to the time the globe of this Earth has existed, as a
world maintaining plants and animals……The solid parts of the present land appear
, in general, to have been composed of the productions of the sea…Hence we find
reason to conclude…….. 2dly. That , before the present land was made,
there had subsisted a world composed of sea and land, in which were tides and currents,
with such operations at the bottom of the sea as now take place. And.
Lastly That, while the present land
was forming at the bottom of the ocean, the former land maintained plants and animals, at
least, the sea was the inhabited by animals, in similar manner as it is at present."
Abstract of a Dissertation, 1785
"This earth, like the body of an
animal is wasted at the same time that it is repaired. It has a state of growth and
augmentation; it has another state, which is that of diminution and decay"….
"We find no vestige of a beginning – no prospect of an end"
Theory of the Earth, 1795.
Hutton’s ideas were being published at
a time of political unrest and controversies were feared. He also has a difficult writing
style. His "Theory of the Earth" ran to 1204 pages. 6 additional chapters were
found a century later. Both these facts led to his initial ideas being dismissed by many.
As Humphrey Davy (1805) states "Dr. Hutton is obscure and perplexed from the
multitude of facts which crowded on his mind." However, his long term friend, John
Playfair translated his ideas into readable English in 1802 as "Illustrations of the
Huttonian Theory" five years after his death.
To summarise, Hutton’s geology rests
on the concept of continuous natural processes working over periods of time that are
infinitely long compared with a human life span. Decay and erosion of the land produce the
sediments and running water moves it to the sea. The internal heat of the earth converts
them from sediments to rocks.
Figure 3 Copy of Hutton's sketch at
Siccar Point (1788)
Figure 3, Siccar Point
- Principle of Faunal succession
The work of Baron Georges Cuvier (1769 – 1832) &
William Smith (1769 – 1839)
Baron Georges Cuvier was born in
Montbeliard in 1769 in what was at that time the Duchy of Wurttemberg to become Germany in
the following century. However following the French Revolution Montbeliard was annexed by
the French and Cuvier became French. He attended school in Stuttgart where he had a broad
education and became fluent in German. This was to stand him in good stead later when he
moved to Paris as few of his colleagues could speak both French and German. At that time
French was the premier language as English is today. This allowed him to be exposed to the
scientific literature of both those central European cultures.
Cuvier had always had an interest in
natural history from a boy and eventually after tutoring in Normandie, he managed to
secure a job after the Terror of the French Revolution, at the Museum National
d’Histoire Naturalle as a junior assistant. This was to become his scientific and
domestic home for the rest of his life. Many publications on comparative anatomy of marine
invertebrates and then mammals followed. His work on the 3 species of elephants and the
fact that mammoths were related to none of them and were extinct caused a stir. He
emphasized the importance of comparative anatomy as a tool for establishing the theory of
the Earth.
His empirical work on the alternation
between freshwater and marine fossils and sediments with Brongniart on the Paris basin and
his rigorous and painstaking analysis of these fossil shells led to his advocacy of
catastrophic events to explain geological phenomena. His assertion that he had discovered
whole fauna of extinct mammals which were distinct from living ones was his primary
concern. The physical cause of the processes, which led to this, were only of secondary
importance to him. Cuvier regarded catastrophies as part of the order of nature
and they had repeatedly occurred in the
course of Earth’s history. Hence we had a faunal succession.
Figure 4 Cuvier's example of an unconformity and faunal
succession
William Smith was styled by Sedgwick
"The father of English Geology"
William Smith was born in Churchill,
Oxfordshire into exactly the opposite type of family on the other side of the English
Channel but in the same year as Cuvier. He was the son of a village blacksmith who died
when he was a young boy. He had to support himself from an early age and was trained as a
surveyor. At this time canal, building was important in Britain and Smith was employed by
companies in this pursuit. He was a keen observer and realized that set faunas followed
one another in strict sequence. Eventually he became confident enough to predict rock
types based on their fossil content. He traveled widely with his work covering as much as
16,000km a year, a huge distance in those days, mostly on horseback. Eventually he
produced the first geological "map of England and Wales with part of Scotland",
in 1815. In 1819, he published part of a work entitled Strata identified by organized
fossils. However William Smith never felt confident about his writing and never joined
a scientific society. His greatest contribution was his field observations and his
synthesis into a geological map.
These three principles apply to sedimentary strata. However
2 other principles are also used. They are
the principles of cross cutting relationships and principle of inclusions.
The Stratigraphic Column
Table 2
The first stratigraphic period to be
recognised was the Tertiary in 1760 by Arduino, a mining expert working in the Venetian
Republic. He distinguished 4 separate stages or orders one above the other. These were
Primary, Secondary, Tertiary and Quaternary, the Atesine Alps, the Alpine foothills, the
sub-Alpine foothills and the plains of the river Po respectively. The second, the
Jurassic, a well-recognised name nowadays, was named by Von Humboldt in 1795, the same
year that James Hutton published his "Theory of the Earth" in Scotland. This was
based on the work done in the Jura Mountains of France. While social revolution surpressed
new stratigraphic idea development in Europe, no new systems were acknowledged. Following
the Treaty of Versailles in 1815, relative time was debated again. In 1822 the
Carboniferous was recognised in Northern England by Conybeare and Phillips and at the same
time the Cretaceous in France by d’Halloy. The majority of period names were then
devised. The last section of the stratigraphic column to be recognised was the Ordovician
in 1879 following the lengthy debate or indeed argument between Sedgwick and Murchison in
Wales. Once the stratigraphic column was complete, type sections could be agreed and
debated.
ABSOLUTE TIME
Introduction
Absolute time had to await the discovery of
radioactivity in 1896 by Antoine-Henri Becquerel and later the recognition that radium
radiates heat continuously by the Curies and Laborde in 1903. The suggestion by Lord
Rutherford in 1903 that radioactive elements could be used to date rocks was revolutionary
and Strutt demonstrated that radioactive elements were widespread in minerals throughout
rocks. In 1907, Bertram Borden Boltwood suggested that the rate of disintegration of
uranium into lead could be used to actually date rocks Thus the higher the percentage of
lead in an ore the older the rock.
With the new radiometric dating methods,
geologists could calibrate the relative scale of geological time thereby creating an
absolute one. Arthur Holmes was the first geologist to construct a time scale (1927),
based on radiometric dating and many time scales have been constructed since for the
Cambrian upwards (Phanerozoic Gk. Plainly evident life). It is being refined even to this
day as more isotopic data become available.
Radiometric dating
Radiometric dating techniques were
developed at the beginning of the 20th century and use the regular rate of
decay of unstable, radioactive elements such as U-235, K-40, Rb-87 and C-14 to their
daughter products either in a single step or through a series of steps. These elements
resemble virtual "clocks" within the earth’s rocks and form the
geologists’ timekeepers. This decay is accompanied by the emission of radiation or
particles (alpha, beta or gamma rays) from the nucleus, by nuclear capture or by ejection
of orbital electrons. Thus heat is given off and this was an important point in the 1903
lecture by Ernest Rutherford when debating the age of the Earth in the company of Lord
Kelvin at the Geological Society of London. If a daughter product is stable, it
accumulates until the parent isotope has completely decayed. If a daughter isotope is also
radioactive, equilibrium is reached when the daughter decays as fast as it formed.
The radioactivity of an element is
described in terms of half-life, the time the element takes to lose 50% of its activity by
decay.
Diagram
This can cover a large scale of time from
billions of years to microseconds. At the end of the period constituting one half-life,
half of what was left is halved again, leaving one quarter of the original quantity and so
on. Every radioactive element has its own half-life e.g. C-14 is 5730 years.
Limitations
There are however some limitations in the use of
radiometric dating.
- The minerals making up the rocks must contain suitable
radioactive elements within their crystal lattices
- The rocks must be the correct age to start with for the
half-life available.
Thus it is useless trying to date a shell 1
million years old with C-14 as there will be no C-14 left. Similarly, it is no good trying
to date pure sandstone composed only of Quartz, SiO2, using the U-235 method,
as Quartz does not normally contain uranium.
Conclusion
Perhaps one of the best known scientists in
the world is Charles Darwin. What is less well known is that he trained as a geologist.
You will hear about a little of his work from John Cartwright. The understanding of the
development of man’s perception of time, both relative and absolute and the age of
the earth have helped us understand the context of our place on the planet on which we
live.
Notes
As well as straight teaching/lecturing, the
2/3 interactive parts to the lecture will be expanded within the workshops. It is hoped
that 3 of the 5 principles will be illustrated in a fieldtrip up the volcano El Teide.
However it is possible to illustrate several principles in an urban setting using building
stones for example the principle of superposition.
BIBLIOGRAPHY
Blundell D.J. and Scott A.C., (1998) Lyell: the past is the
key to the present, Geological Society of London, ISBN 1862390185
Bowler P, (1992) The fontana history of the environmental
sciences, Fontana Press ISBN 0006861849
Craig G.Y. and Hull J.H., (1998), James Hutton - Present
and future, Geological Society of London, ISBN 1862390266
Dean D., (1992), James Hutton and the history of geology,
Cornell University Press, ISBN 0801426669
Hallam A., (1984), Great Geological controversies, Oxford
University Press, ISBN 0198544308
Hellman H., (1998), Great Feuds in science, Ten of the
liveliest disputes ever, John Wiley, ISBN 04714169803
Holland C.H., (1999), The idea of time, John Wiley, ISBN
0471985457
Oldroyd D., (1996), Thinking about the Earth: a history of
ideas in geology, Athlone Press, ISBN 0485114321
Playfair, J. (1805), Biographical account of the late Dr.
James Hutton, F.R.S. Edin., Transactions of the Royal Socieety of Edinburgh, V,
(III),39-99.
Rudwick M.J.S., (1997), Georges Cuvier, fossil bones and
geological catastrophes, University of Chicago Press, ISBN 0226731073
Workshop
The workshops will involve
- A loud ticking clock and a timer set for one hour
- Perhaps a sand hour glass if available
- a piece of string measured at various intervals to show
prominent earth events,
- 2 members of the audience (if not already done in the
lecture)
- a cartoon geological cross section
This has then introduced the audience to the 2 ways of
looking at geological time.
The last two principles will hopefully be illustrated in
the field at Mount Teide and in the workshop exercise.
- Principle of cross cutting relationships
- Principle of inclusions.
It will be possible to illustrate at least one of these on
the field excursion. It will be shown how these can be illustrated in an urban environment
using windows and doorways in a building.
Workshops
Activity 1
Length of string exercise
The string and significant dates can be varied depending on
the country in which this exercise is being done (e.g. Black Death). Obviously, the events
on the string could vary between Britain and for example Spain or Greece. Use a scale of 1
cm per 1000 years. This is significant as it will be the year 2001.
| Event
|
Years Ago |
| Today, |
0 |
| Birth of Jesus Christ, |
2,000 |
| Age of the Earth according
Archbishop Ussher |
6000 |
| End of Ice age in Northern Europe,
|
10,000 |
| Evidence of first Homo sapiens in
Europe, |
500,000 |
| Tenerife |
8,500,000 |
| Gran Canaria 1 |
3,500,000 |
| Extinction of dinosaurs |
65,000,000 |
| Age of the earth according to Lord
Kelvin (1846) |
100,000,000 |
| Age of the earth according to Lord
Kelvin (1866) |
20-400,000,000 |
| First appearance in fossil record
of multicellular algae |
2,100,000,000 |
| Oldest rock on earth |
3,800,000,000 |
| Birth of Earth |
~ 4,600,000,000 |
Activity 2
Bible exercise
Natural scientists were interested throughout the 16th,
17th centuries to know the age of the earth and many calculations were
produced. However in 1658 Archbishop Ussher came up with a date which the whole of the
Christian world seemed to initially accept. How did Archbishop Ussher of Armagh come up
with 09.00 26th October 4004BC in 1658?
An analysis of the first book of the Old Testament seems
the obvious place to start. The beginning of Genesis details the creation and then goes on
to list in detail Adam and his decendants. Students will try to calculate how many years
are accounted for in the Old Testament of the bible.
A discussion will then take place as to why there might be
a discrepancy both between student group addition! And Archbishop Ussher's calculation.
What else could scientists of that time be concerned about and where do the errors arise.
Activity 3
Cartoon cross section exercise. What happened first?
| Work out the geological sequence of the section and decide
which principles could have been used at the following dates |
| 1000AD |
| 1500AD |
| 1832AD |
Table 1 List of principle players on the stage
| Name |
Dates |
Nationality/place
of work |
| Leonardo di Vinci |
1452-1519 |
Italian/Apennines, N. Italy |
| Archbishop James Ussher |
1581-1656 |
Irish, age of the earth (bible) |
| Robert Hooke |
1635-1703 |
English/Faunal succession hints |
| Nicholaus (Neils) Steno |
1638-1687 |
Dane/Italy |
| G. Arduino |
1714-1795 |
Italian/Venice |
| James Hutton |
1726-1797 |
Scottish/Scotland |
| Alexander von Humboldt |
1769-1859 |
German |
| Georges Cuvier |
1769-1832 |
French/Paris basin |
| William Smith |
1769-1839 |
English/England |
| William Buckland |
1784-1846 |
English |
| Adam Sedgwick |
1785-1873 |
English/ England & North Wales |
| Roderick Murchison |
1792-1871 |
English/ South Wales |
| Charles Lyell |
1797-1875 |
Scottish/England |
| Lord Kelvin (William Thomson) |
1824-1907 |
Scottish |
| Archibald Geike |
1835-1924 |
Scottish/Scotland |
| Charles Lapworth |
1842-1920 |
English/Mid Wales |
| Pierre Curie |
1859-1906 |
French/Paris |
| (Lord Rayleigh) Ernest Rutherford |
1871-1937 |
English |
| Arthur Holmes |
1890-1965 |
English |
| James Croll |
1921-1990 |
Scottish/Scotland |
Table
2 STRATAGRAPHIC COLUMN
| 1970Neogene Quaternary |
Néogène: Quaternaire |
Neogeno: Cuaternario |
1829 Desnoyers; 1833 Reboul (redefined) |
| Pleistocene |
Pleistocéne |
Pleisteceno |
1833 Charles Lyell |
| Pliocene |
Pliocéne |
Plioceno |
1833 Charles Lyell |
| Miocene |
Miocéne |
Mioceno |
1833 Charles Lyell |
---------- |
---------- |
---------- |
|
| 1970 Paleogene Oligocene |
Paléogène Oligocéne |
Paleogen: Oligoceno |
1854 H. Von Beyrich |
| Eocene |
Eocéne |
Eoceno |
1833 Charles Lyell |
| Palaeocene |
Palaeocéne |
Paleoceno |
1874 W.P.Schimper |
---------- |
---------- |
---------- |
|
| Cretaceous |
Crétacé |
Cretàcico |
1822 Omalius d'Holloy |
| Jurassic |
Jurassique |
Juràsico |
1795 Alexander von Humboldt. |
| Triassic |
Trias |
Triàsico |
1834 F. Von Alberti |
---------- |
---------- |
---------- |
|
| Permian |
Permien |
Pérmico |
1841 Murchison |
| Carboniferous (Pennsylvanian Mississippian) |
Carbonifére |
Carbonifero |
1822 British consensus 1953 US division |
| Devonian |
Devonien |
Devonico |
1840 Murchison & Sedgewick |
| Silurian |
Silurien |
Silurico |
1835 Sedgewick & Murchison 1839 Global recognition Murchison |
| Ordovician |
Ordovicien |
Ordovicico |
1902 Charles Lapworth |
| Cambrian |
Cambrien |
Càmbrico |
1835 Sedgewick & Murchison |
---------- |
---------- |
---------- |
|
| Precambrian |
Precambrien |
Precàmbrico |
|
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