Michael Benton, Ph.D., is a vertebrate paleontologist with
particular interests in dinosaur origins and fossil.
Accuracy of Fossils and Dating
Methods
Michael Benton
An ActionBioscience.org original article
articlehighlights
Fossil dating is accurate since the method follows strict scientific guidelines:
 the age of rocks around a fossil can be considered
 mathematical calculations are used
 the state of decay, carbon-14, and isotopes figure in
calculations
 tree of life relationships often help sort the dates
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
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learn more
get involved
nuary 2001
Fossils provide a record of the history of life.
Our understanding of the shape and pattern of the history of life depends on the accuracy
of fossils and dating methods. Some critics, particularly religious fundamentalists, argue
that neither fossils nor dating can be trusted, and that their interpretations are better.
Other critics, perhaps more familiar with the data, question certain aspects of the quality
of the fossil record and of its dating. These skeptics do not provide scientific evidence for
their views. Current understanding of the history of life is probably close to the truth
because it is based on repeated and careful testing and consideration of data.
The rejection of the validity of fossils and of dating by religious fundamentalists creates a
problem for them:
Millions of fossils have been discovered.

They cannot deny that hundreds of millions of fossils reside in display cases and
drawers around the world. Perhaps some would argue that these specimens - huge
skeletons of dinosaurs, blocks from ancient shell beds containing hundreds of
specimens, delicately preserved fern fronds — have been manufactured by scientists to
confuse the public. This is clearly ludicrous.
Some skeptics believe that all fossils are the same age.

Otherwise, religious fundamentalists are forced to claim that all the fossils are of
the same age, somehow buried in the rocks by some extraordinary catastrophe,
perhaps Noah’s flood. How exactly they believe that all the dinosaurs, mammoths, early
humans, heavily-armored fishes, trilobites, ammonites, and the rest could all live
together has never been explained. Nor indeed why the marine creatures were
somehow ‘drowned’ by the flood.
Rejecting fossil data cannot be supported by proof.

The rejection of dating by religious fundamentalists is easier for them to make,
but harder for them to demonstrate. The fossils occur in regular sequences time after
time; radioactive decay happens, and repeated cross testing of radiometric dates
confirms their validity.
Fossils occur in sequences
Fossil sequences were recognized and established in their broad outlines long before
Charles Darwin had even thought of evolution. Early geologists, in the 1700s and 1800s,
noticed how fossils seemed to occur in sequences: certain assemblages of fossils were
always found below other assemblages. The first work was done in England and France.
Fossil hunting began by accident in England around 1800.

Around 1800, William Smith in England, who was a canal surveyor, noticed that
he could map out great tracts of rocks on the basis of their contained fossils. The
sequences he saw in one part of the country could be correlated (matched) precisely
with the sequences in another. He, and others at the time, had discovered the first
principles of stratigraphy — that older rocks lie below younger rocks and that fossils
occur in a particular, predictable order.
Stratigraphy, the study of rock layers, led to paleontology, the study of fossils.

Then, geologists began to build up the stratigraphic column, the familiar listing of
divisions of geological time — Jurassic, Cretaceous, Tertiary, and so on. Each time unit
was characterized by particular fossils. The scheme worked all round the world, without
fail.

From the 1830s onwards, geologists noted how fossils became more complex
through time. The oldest rocks contained no fossils, then came simple sea creatures,
then more complex ones like fishes, then came life on land, then reptiles, then
mammals, and finally humans. Clearly, there was some kind of ‘progress’ going on.

All became clear, of course, in 1859 when Charles Darwin published his “On the
origin of species”. The ‘progress’ shown by the fossils was a documentation of the grand
pattern of evolution through long spans of time.
Accuracy of the fossils
Fossils prove that humans did not exist alongside dinosaurs.
Since 1859, paleontologists, or fossil experts, have searched the world for fossils. In the
past 150 years they have not found any fossils that Darwin would not have expected.
New discoveries have filled in the gaps, and shown us in unimaginable detail the shape of
the great ‘tree of life’. Darwin and his contemporaries could never have imagined the
improvements in resolution of stratigraphy that have come since 1859, nor guessed what
fossils were to be found in the southern continents, nor predicted the huge increase in
the number of amateur and professional paleontologists worldwide. All these labors have
not led to a single unexpected finding such as a human fossil from the time of the
dinosaurs, or a Jurassic dinosaur in the same rocks as Silurian trilobites.
Scientists now use phylogeny, mathematics, and other computations to date
fossils.
Paleontologists now apply sophisticated mathematical techniques to assess the relative
quality of particular fossil successions, as well as the entire fossil record. These
demonstrate that, of course, we do not know everything (and clearly never will), but we
know enough. Today, innovative techniques provide further confirmation and
understanding of the history of life. Biologists actually have at their disposal several
independent ways of looking at the history of life - not only from the order of fossils in
the rocks, but also through phylogenetic trees.

Phylogenetic trees are the family trees of particular groups of plants or animals,
showing how all the species relate to each other.

Phylogenetic trees are drawn up mathematically, using lists of morphological
(external form) or molecular (gene sequence) characters.

Modern phylogenetic trees have no input from stratigraphy, so they can be used
in a broad way to make comparisons between tree shape and stratigraphy.

The majority of test cases show good agreement, so the fossil record tells the
same story as the molecules enclosed in living organisms.
Accuracy of dating
Dating in geology may be relative or absolute. Relative dating is done by observing
fossils, as described above, and recording which fossil is younger, which is older. The
discovery of means for absolute dating in the early 1900s was a huge advance. The
methods are all based on radioactive decay:
Fossils may be dated by calculating the rate of decay of certain elements.

Certain naturally occurring elements are radioactive, and they decay, or break
down, at predictable rates.
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
Chemists measure the half-life of such elements, i.e., the time it takes for half of
the radioactive parent element to break down to the stable daughter element.
Sometimes, one isotope, or naturally occurring form, of an element decays into
another, more stable form of the same element.
By comparing the proportions of parent to daughter element in a rock sample,
and knowing the half-life, the age can be calculated.
Older fossils cannot be dated by carbon-14 methods and require radiometric
dating.
Scientists can use different chemicals for absolute dating:


The best-known absolute dating technique is carbon-14 dating, which
archaeologists prefer to use. However, the half-life of carbon-14 is only 5730 years, so
the method cannot be used for materials older than about 70,000 years.
Radiometric dating involves the use of isotope series, such as rubidium/strontium,
thorium/lead, potassium/argon, argon/argon, or uranium/lead, all of which have very
long half-lives, ranging from 0.7 to 48.6 billion years. Subtle differences in the relative
proportions of the two isotopes can give good dates for rocks of any age.
Scientists can check their accuracy by using different isotopes.
The first radiometric dates, generated about 1920, showed that the Earth was hundreds
of millions, or billions, of years old. Since then, geologists have made many tens of
thousands of radiometric age determinations, and they have refined the earlier
estimates. A key point is that it is no longer necessary simply to accept one chemical
determination of a rock’s age. Age estimates can be cross-tested by using different
isotope pairs. Results from different techniques, often measured in rival labs, continually
confirm each other.
There is only a 1% chance of error with current dating technology.
Every few years, new geologic time scales are published, providing the latest dates for
major time lines. Older dates may change by a few million years up and down, but
younger dates are stable. For example, it has been known since the 1960s that the
famous Cretaceous-Tertiary boundary, the line marking the end of the dinosaurs, was 65
million years old. Repeated recalibrations and retests, using ever more sophisticated
techniques and equipment, cannot shift that date. It is accurate to within a few thousand
years. With modern, extremely precise, methods, error bars are often only 1% or so.
Conclusion: The strict rules of the scientific method ensure the accuracy of fossil
dating.
Conclusion
The fossil record is fundamental to an understanding of evolution. Fossils document the
order of appearance of groups and they tell us about some of the amazing plants and
animals that died out long ago. Fossils can also show us how major crises, such as mass
extinctions, happened, and how life recovered after them. If the fossils, or the dating of
the fossils, could be shown to be inaccurate, all such information would have to be
rejected as unsafe. Geologists and paleontologists are highly self-critical, and they have
worried for decades about these issues. Repeated, and tough, regimes of testing have
confirmed the broad accuracy of the fossils and their dating, so we can read the history of
life from the rocks with confidence.
© 2001, American Institute of Biological Sciences. Educators have permission to reprint
articles for classroom use; other users, please contact editor@actionbioscience.org for
reprint permission. See reprint policy.
Michael Benton, Ph.D., is a vertebrate paleontologist with particular interests in
dinosaur origins and fossil history. Currently, he is studying certain basal dinosaurs from
the Late Triassic and the quality of different segments of the fossil record. He holds the
Chair in Vertebrate Paleontology at the University of Bristol, UK, in addition to chairing
the Masters program in paleobiology at the university. He has written some 30 books on
dinosaurs and paleobiology, ranging from professional tomes to popular kids’ books.
http://www.gly.bris.ac.uk/www/admin/personnel/MJB.html
Accuracy of Fossils and Dating
Methods
Fossils and evolution
Michael Benton wrote another article, Evidence of Evolutionary Transitions, for this
website which explains how fossils support the stages of evolutionary history.
http://www.actionbioscience.org/evolution/benton2.html
Stratigraphy and the succession of rocks
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» The geologic time scale — basics and history, and the latest standard time
scale.
http://pubs.usgs.gov/gip/geotime/contents.html
» The stratigraphic column: explanation and graphic illustration. The second link
provides a graphic explanation of a stratigraphic column of Iowa, USA.
http://www.priweb.org/ed/pgws/geology/stratigraphic_column.html
http://www.igwa.org/iowacol.asp
»
A
fun
kid’s
site
about
geologic
time.
http://www.zoomwhales.com/subjects/Geologictime.html
»
Learn
the
names
of
the
divisions
of
geologic
time.
http://www.ucmp.berkeley.edu/exhibit/geology.html
»
A
basic
outline
of
geological
time
and
links.
http://www.geo.ucalgary.ca/~macrae/timescale/timescale.html
http://www.es-designs.com/geol105/timescale/
Quality of the fossil record
Data bases and software for studying the quality
http://palaeo.gly.bris.ac.uk/cladestrat/cladestrat.html
of
the
fossil
record.
Radiometric dating methods and their quality


»
The
basics.
http://pubs.usgs.gov/gip/geotime/radiometric.html
» Good overview with response to critiques by religious fundamentalists.
http://www.talkorigins.org/faqs/dating.html
Read a book
Michael Benton has written over 30 books on dinosaurs and paleobiology. Two suggested
readings are provided — the first for adults, the second for children:


» Vertebrate Palaeontology (Stanley Thornes Pub., 2000) traces the history of the
vertebrates for amateurs as well as professionals, and explains how research scientists
obtain paleobiological information.
» Dinosaur and Other Prehistoric Animal Factfinder (Kingfisher Books, 1998) is a
resource for youngsters who are serious about dinosaurs, with illustrations that are
detailed and colorful and hundreds of different creatures profiled in depth (written with
Ralph Orme).
getinvolved links
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learn more
references
top
Where to see dinosaurs
An
online
directory
of
dinosaur
exhibits
fro
http://www.dinodirectory.com/index.php?t=sub_pages&cat=8
around
the
world.
Dinosaur expeditions
Many natural history museums and universities worldwide offer public participation
programs in dinosaur events, such as fossil hunting or fossil cataloguing. No experience
needed in most cases! The list is too long to mention here, so a couple of examples are
provided to get you going on your search for programs in your area:


»
Dinosaur
Provincial
Park
in
Alberta,
Canada
http://www.cd.gov.ab.ca/enjoying_alberta/parks/featured/dinosaur/flashindex.asp
»
The
Museum
of
Western
Colorado
in
Grand
Junction
http://www.dinodigs.org/index.htm
Discovering fossils
Explore U.K. fossil collecting locations that are detailed on this site. Also includes info on
how fossils are formed, the “cleaning, preparing, & repairing” of fossils, and other useful
resources.
http://www.discoveringfossils.co.uk/
Educators: Classroom lessons
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»
Deep
Time
interactive
lesson
This lesson informs students about the dating methods that enable science to have a
high level of confidence in the geological ages of an old Earth. At the same time, it
discusses how pseudoscience can misrepresent geological dating. Also check out the link
to an online interactive tutorial on half-lives, Carbon 14 dating, and how isochron dating
is
done.
http://www.indiana.edu/~ensiweb/lessons/deep.les.html
»
Creating
a
stratigraphic
column
Grades 7-12 Earth Science activity “to enable students to construct a stratigraphic
column of an outcrop and understand sedimentary depositional processes.”
http://www.chipr.sunysb.edu/eserc/SummerEducationalInterns/Linda/index.html
»
Geological
Time:
What
Can
We
Learn
from
Fossils?
A complete unit where students analyze data and construct an age-depth plot. Grades
7-12;
from
Texas
A&M
University.
http://oceandrilling.coe.tamu.edu/curriculum/Geological_Time/Fossil_Data/presentation
.html
»
Fossil
Dating
and
the
Geological
Timeline
Several “activities and information about dating fossils and placing them in the context
of the history of life on Earth.” Includes background information for teachers. For grades
5-8,
but
activities
can
be
easily
modified
for
higher
grades.
http://www.acad.carleton.edu/curricular/BIOL/classes/bio302/Pages/TKpage2.html
articlereferences
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learn more
get involved
top
General references:

» Benton, M. J., Wills, M. and Hitchin, R. 2000. “Quality of the fossil record through time.”
Nature 403, 534-538.

» Benton, M.J., David A.J. Harper, and David Benton. 1997. Basic Paleontology. AddisonWesley Pub. Co.

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
» Jackson, Julia ed. 1997. Glossary of Geology, 4th ed. American Geological Institute.
» McClay, Ken. 1991. The Mapping of Geological Structures. John Wiley & Sons, Ltd.
» O’Brien, M.J. and R.L. Lyman. 1999. Seriation, Stratigraphy, and Index Fossils - The
Backbone of Archaeological Dating. Kluwer Academic Publishers.

» William Smith’s biography: http://www.ucmp.berkeley.edu/history/smith.html