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Relative dating provided a history of life on Earth, a history that clearly showed changes in geology, climate, and life. Today radiometric dating places absolute dates on the relative time scale. There were many early attempts at establishing an absolute time scale before the use of radiometric dating. Some of these efforts were biblically based while others represented non-religious estimates. We will survey the work of specific individuals to explore a variety of strategies.
Biblical Chronology
James Ussher (1581-1656) Archbishop of Armagh (Ireland) developed
a chronology, entitled Annalium pars postierior in 1654, based
upon the life spans of people in the Bible and other ancient
documents. Ussher calculated the date of creation to have been
nightfall preceding October 23, 4004 BC. The 9:00 a.m. time
of creation often attributed to Ussher was actually from previous
work by John Lightfoot (1602-1675) a distinguished biblical
and Greek scholar (Dalrymple, 1991, p. 21).
Decline in Sea Level
Benoit de Maillet (1656-1738) was a French anthropologist and
diplomat. de Maillet estimated the Earth was 2 billion years
old. de Maillet's estimate was based upon declining sea levels.
Fossils of ocean organisms on land and in the mountains seemed
to support that the Earth was once covered by one large ocean.
As this ocean evaporated, water levels declined. de Maillet
used measured sea level changes to estimate when the Earth
was completely covered with water. This theory was based on
Descartes theory on the birth and death of the sun and planets.
de Maillet's estimate was presented in a fictional conversation
between a French missionary and an Indian philosopher Telliamed
(de Maillet spelled backwards). de Maillet never published
his work for fear of repercussions. Telliamed was published
by Abbé J.B. le Mascrier in 1748. le Mascrier did not
publish under his real name and changed the estimate from millions
to billions. Telliamed was not published in its original format
until 1968. Although de Maillet’s formulations were made
without knowledge of geological uplift they were important
because they represented logical extrapolations from measurements
taken from nature. Furthermore, de Maillet’s method excluded
human life spans as a measurement (Dalrymple 1991, p.27). The
dynamic nature of Earth’s surface was unknown to Maillet,
but even during his time it was known that sea levels had dropped
in some areas and were rising in others. Sea level change was
quickly abandoned as an Earth dating method.
Cooling of Earth
Georges-Louis Lecterc, Comte de Buffon (1707-1788) was a French
naturalist. Buffon calculated the world to be much older than
Ussher. In his 1778 publication Epochs of Nature Buffon calculated
the age of the Earth to be 75,000 years. Buffon arrived at
this age by heating small iron spheres and scaling their cooling
rates to an earth-sized mass. Sir Isaac Newton was the first
to suggest using this strategy to estimate the cooling rate
of Earth. The Catholic Church in France condemned Buffon for
his calculation and burned his books. Lord Kelvin would later
greatly increase the precision of Buffon’s crude methods
(Burchfield 1990, p. 34). Kelvin’s methods were mathematically
elegant and deductively sound; however, without the knowledge
of energy created from radioactive decay his premises and thus
his conclusions were wrong. Cooling of the Earth has been abandoned
as a method to determine Earth’s age.
Cooling of Sun
Hermann Ludwig Ferdinand von Helmholtz (1821-1894) was a German
physician and physicist. Helmholtz used the cooling of the
sun to estimate Earth's age. In 1856 Helmoltz calculated that
it would take the Sun 22 million years to condense down to
its current diameter and temperature from a nebula of dust
and gas. He assumed the heat of the sun was generated from
gravitational contraction. Lord Kelvin’s version of the
Helmholtz model included heat generated by meteoric impacts.
The gravitational potential energy of the meteor would be converted
to kinetic energy and upon collision into heat energy. Although
meteoric impact was not supported by the observations made
by astronomers Kelvin could see no alternative to gravitational
potential energy (Bachall, 2000). Kelvin’s calculations
indicated that even the most vigorous chemical reactions could
not account for the known age of human civilization, thus chemical
reactions could not be a heat source for the sun. With the
discovery of nuclear reactions the model developed by Helmholtz
and Kelvin became obsolete.
Weathering & Erosion
Charles Darwin speculated on the weathering and erosion of the
Weald Chalk formations in his book The Origin of Species by
Means of Natural Selection. Chalk formations in North and South
Downs at one time extended over the sandstone and clay layers
of the High and Low Weald forming a dome. This chalk layer
was eroded and now only exits at the edges. Darwin sets up
his scientific intuition from his personal geologic field observations.
Darwin asks the reader to imagine the immense time needed to
weather, erode, and deposit rock. Darwin turns attention to
the chalk formations of the Weald and, with what he argues
are reasonable rates of weathering and erosion, concludes the
denudation of the Weald required 300,000,000 million years
(Darwin 1859/2004, pp. 230-232). Although not an estimate for
the age of Earth, Darwin’s reasoning represents an interesting
attempt at using denudation (exposing of rock strata through
erosion) to date a rock formation. Kelvin was critical of Darwin’s
estimate when writing on the age of the Sun though cooling.
Kelvin believed that the Sun could not have existed for the
time required by Darwin’s theory; he was working without
knowledge of nuclear energy. Darwin was so shaken by Kelvin’s
criticism that he removed his estimate in later editions of
the Origin of Species (Bachall 2000). Kelvin’s impressive
mathematical models based on physics also influenced the science
of geology in both positive and negative ways. The limits Kelvin’s
quantitative methods placed on Earth’s age had the unfortunate
effect of making uniformatarianism less tenable. Due to Kelvin’s
work the science of geology became more quantitative and geologists
and physicists interacted with each other (Burchfield 1990,
pp. 10-12). It was clear to both sides that scientific hypotheses
and theories must be internally coherent and externally consistent
with findings in other fields of science.
Sediment Accumulation
John Phillips (1800-1874) was an English geologist. Phillips
came under the charge of his uncle William Smith (the father
of modern geology) when his parents died. In 1860 Phillips
utilized sediment accumulation to estimate the Earth's age
at 38 to 96 million years. As a method of determining the age
of the Earth, sediment accumulation involved comparing measured
rates of continental erosion with the aggregate thickness of
sedimentary rock layers from successive time divisions. Charles
D. Walcott (1850-1927) an American geologist and paleontologist
is probably best known for his discovery and subsequent work
on fossils of the Burgess Shale formation of British Columbia,
Canada. Walcott made the most detailed model of sediment accumulation
(Dalrymple 1991, pp. 59-66). Walcott’s estimate was between
35 and 80 million years. Many uncertainties plagued this method
of age determination. These uncertainties included the relationship
between areas of erosion and areas of deposition, the rates
of sedimentation, and the missing time represented by unconformities,
etc. (Burchfield 1990, pp. 16-18). Furthermore, this method
could only attempt to reach back to the Cambrium period. These
rock layers did not reveal the majority of Earth’s history
(Dalrymple 1991, pp 68-69). Sediment accumulation was eventually
abandoned as a method to determine the age of the Earth.
Tidal Effects
William Thompson, Lord Kelvin (1824-1907) was an Irish mathematician,
physicist and engineer. Between the years of 1862 and 1897
Kelvin used multiple methods to calculate the age of the Earth.
These methods included cooling of the Earth, Sun, and Earth
tidal effects. Immanuael Kant (1724-1804) a German philosopher
was the first to recognize the breaking effect of the tides
on Earth’s rotation. Kelvin was the first to Estimating
Earth's age using tidal effects (Dalrymple, 1991, p. 48). As
the tides rise and fall gravitational friction causes a reduction
in
the Earth’s
rotation, Moons orbital velocity and an increase in the Moon’s
distance from Earth. Kelvin was the first to show that a transfer
of angular momentum from the Earth to the Moon caused the Moon
to recede from the Earth. Kelvin's estimates using these different
methods ranged from 10 million to less than 1 billion years.
The 1 billion year figure was arrived at using tidal effects.
George H. Darwin (1845-1912) a mathematical astronomer was
the son of Charles Darwin. G.H. Darwin refined the method of
determining Earth’s age using tidal effects to a high
degree (Dalrymple 1991, pp 47-52). Darwin’s minimum age
for the Earth using this method was 56 million years. Darwin
believed the Earth was most likely much older. Using the Moon’s
recession rate from the Earth due to tidal effects did not
become an accurate method for determining Earth’s age
until the movement of the continents described by Plate Tectonic
theory became part of the mathematical model during the 1960’s.
The current model is supported by paleontological evidence
in the form of tidal rhythmites or tidally laminated sediments
(Thompson, 1999). The current age of the Earth using this model
is in agreement with radiometric dating.
Salt Accumulation in Oceans
Edmund Halley (1656-1742) was an English Astronomer. In 1715
Halley hypothesized that the age of the Earth could be calculated
by determining the rate at which salt is added to the ocean
through erosion. Halley recommended that salt concentrations
be measured on a regular basis to establish the rate at which
they were added so that future scientists could use his method.
Thomas Mellard Reade (1832-1909) an English geologist was the
first to apply Halley’s suggestion of using the oceans
as a sort of “salt clock” in 1876. Instead of using
changes in salt concentrations over time as suggested by Halley,
Reade used estimates for the amount of salts added by erosion.
Reade knew the estimated amounts of chloride and sulfate salts
added to the oceans from the major rivers of the world. He
used this data to determine how long it would take the ocean
to reach its present salt concentrations. His estimate was
25 million years for sulfates and 200 million years for chlorides
(Dalyrumple 1991, p. 53). Reade called his salt clock model “chemical
denundation”. John Joly (1857-1933) an English geologist
would refine Reade’s model. Jolly used sodium concentrations
as his salt clock because he believed that sodium is added,
but not withdrawn from the oceans. Jolly’s estimate for
Earth’s age was 90 to 100 million years. Today we know
that the salts are not only added but also removed from the
ocean. Salt accumulation in the oceans was abandoned as a way
to determine Earth’s age.
Eccentricity
of Mercury’s
Orbit
In 1918 Harold Jeffreys (1891-1989), British Astronomer and Geophysicist,
used the changing eccentricity of Mercury's orbit
over time to estimate the age of our solar system to be 3 billion
years (Dalrymple, 1991, p. 17). All of the above methods would
become obsolete with the discovery of radioactivity.
Bibliography:
Bachcall, J.N. (2000). How the Sun Shines. Published on Nobelprize.org. see http://nobelprize.org/nobel_prizes/physics/articles/fusion/index.html
Burchfield, J.D. (1990). Lord Kelvin and the Age of the Earth. Chicago: The University of Chicago Press.
Dalrymple, G. B. (1991). The Age of the Earth. Stanford California: Stanford University Press.
Darwin, C. (2004). The Origin of Species. New York: Fine Creative Media. (Originally published in 1859).
Geology of the Weald printed on Highweald.org see: http://www.highweald.org/text.asp?PageId=256
Thompson, T. (1999). The Recession of the Moon and the Age of
the Earth-Moon System. The TalkOrigin Archieves see: http://www.talkorigins.org/faqs/moonrec.html
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