Dating carbon 14 dating
Scientists have calculated the age of our planet to be approximately 4.5
billion years. But how did scientists determine that age? The answer is
complicated: It involves everything from observation to complicated
mathematics to understanding the elements that make up our planet. In the
1800s, as scientists sought to determine the age of the planet, they made a
few missteps. In 1862, a famous Irish physicist and mathematician, Lord
Kelvin, estimated that Earth was between 20-million and 400-million years
old. While that is an enormous span of time, even an age of 400 million
years would make the planet quite young in relation to the rest of the
universe. Lord Kelvin based his conclusion on a calculation of how long it
would have taken Earth to cool if it had begun as a molten mass. While his
estimate was wrong by a significant margin, his technique of drawing
conclusions based on observations and calculations was an accurate
scientific method.
Scientists also tried to use relative dating techniques to determine the
age of the planet. *Stratigraphy *compares the configuration of layers of
rock or sediment in order to determine how old each layer is in relation to
one another. This technique can reveal which layers are older or which
events happened before others if the layers of sediment have remained in
sequential order. Layers can be rearranged, bent, or contain
inconsistencies. However, stratigraphy yields no exact age for those layers
or events. Nonetheless, even though this technique did not give scientists
the precise number they were looking for, it did suggest that Earth was
most likely billions of years old, and not just millions as was previously
thought.
As advances in chemistry, geology, and physics continued, scientists
found a method by which the absolute age—an actual number of years—of a
rock or mineral sample could be determined. This method is *called
radiometric dating*, and it involves the decay, or breakdown, of
radioactive elements. Using radiometric dating techniques, it became
possible to determine the actual age of a sample.
Radiometric dating requires an understanding of isotopes. *Isotopes *are
variations of an element differentiated by the number of neutrons in their
nuclei. The isotopes of unstable radioactive elements—known as parent
isotopes—eventually decay into other, more stable elements—*known as
daughter isotopes*—in a predictable manner, and in a precise amount of time
called a half-life. The half-life of an element is the amount of time
required for exactly half of a quantity of that element to decay. The age
of a sample can be determined based on the ratio of parent to daughter
isotopes within the sample.
One problem with this approach to dating rocks and minerals on
Earth is the presence of the rock cycle. During the rock cycle, rocks are
constantly changing between forms, going back and forth from igneous to
metamorphic to sedimentary. Old rocks may even be destroyed as they slide
back into Earth’s mantle, to be replaced by newer rocks formed by
solidified lava. This makes finding an exact age for Earth difficult,
because the original rocks that formed on the planet at the earliest stages
of its creation are no longer here. The oldest rocks that have been found
are about 3.8-billion years old, though some tiny minerals have been dated
at 4.2 billion years. To get around the difficulty presented by the rock
cycle, scientists have looked elsewhere in the solar system for even older
rock samples. They have examined rocks from the moon and from meteorites,
neither of which have been altered by the rock cycle. {KR However how is
one sure rock in space also do not change?} The same techniques of
radiometric dating have been used on those rocks. All the data from Earth
and beyond has led to the estimated age of 4.5 billion years for our planet.
Why can't we carbon date after 1950?
The spike in atmospheric carbon-14 levels during the 1950s and early 1960s
makes this approach possible, but it also means it will have a limited
period of utility because the amount of carbon-14 in the atmosphere is
slowly returning to its natural level. Carbon dating is used now for almost
everything old that people want to date. It is taken as fact and used as
evidence to gather information on the world and past civilizations.
However, Carbon dating is at best a good theory, and that is all it is, a
theory. Too many people forget the definition of a theory. Because of the
short length of the carbon-14 half-life, carbon dating is only accurate for
items that are thousands to tens of thousands of years old. Most rocks of
interest are much older than this. Geologists must therefore use elements
with longer half-lives. Carbon-14 has a half life of about 5730 years. We
can use the estimated ratio of carbon-12 to carbon-14 during a specific
time period and compare it to the measured ratio. By doing this we can see
how old a specimen is. This is highly accurate, until you start getting
into the tens of thousands of years old. What can be dated? For radiocarbon
dating to be possible, the material must once have been part of a living
organism. This means that things like stone, metal and pottery cannot
usually be directly dated by this means unless there is some organic
material embedded or left as a residue.
What are the problems with fossil dating methods?
A common problem with any dating method is that a sample may be
contaminated with older or younger material and give a false age. This
problem is now reduced by the careful collection of samples, rigorous
crosschecking and the use of newer techniques that can date minute
samples.
Concerning the age of the Earth, the Bible's genealogical records
combined with the Genesis 1 account of creation are used to estimate an age
for the Earth and universe of about 6000 years, with a bit of uncertainty
on the completeness of the genealogical records, allowing for a few
thousand years more. For example, Muslim
<https://www.britannica.com/topic/Islam> scholars note that the Qurʾān
<https://www.britannica.com/topic/Quran>, or Koran, hints that each of the
six days of creation <https://www.britannica.com/topic/creation-myth> presented
in the biblical book of Genesis
<https://www.britannica.com/topic/Genesis-Old-Testament> lasted somewhere
between 1,000 and 50,000 years, but there are few other references to
Earth’s age in Islamic tradition. According to some Hindu
<https://www.britannica.com/topic/Hinduism> texts, Earth has been around
for more than 150 trillion (with a *t*) years!
The invention of radiocarbon dating elegantly merged chemistry and
physics to develop a scientific method that can accurately determine *the
age of organic materials as old as approximately 60,000 years.*
It is based on the fact that living organisms—like trees, plants, people,
and animals—absorb carbon-14 into their tissue. When they die, the
carbon-14 starts to change into other atoms over time. Scientists can
estimate how long the organism has been dead by counting the remaining
carbon-14 atoms. The technique was developed in the late 1940s at the
University of Chicago by chemistry professor Willard Libby, who would later
receive the Nobel Prize for the work.
The breakthrough introduced a new scientific rigor to archaeology, allowing
archaeologists to put together a history of humans across the world, but it
had a significant effect in other fields, too. Carbon dating has helped us
reveal how our bodies work, to understand the climate of the Earth and
reconstruct its history, and to track the sun’s activity
<https://news.uchicago.edu/explainer/what-is-solar-wind> and the Earth’s
magnetic fields. Radiocarbon dating was also instrumental in the discovery
of human-caused climate change, as scientists used it to track the sources
of carbon in the atmosphere over time.
It starts with cosmic rays—subatomic particles of matter
that continuously rain upon Earth from all directions. When cosmic rays
reach Earth’s upper atmosphere, physical and chemical interactions form the
radioactive isotope carbon-14.
Living organisms absorb this carbon-14 into their tissue. Once they die,
the absorption stops, and the carbon-14 begins very slowly to change into
other atoms at a predictable rate. By measuring how much carbon-14 remains,
scientists can estimate how long a particular organic object has been dead.
>From there, the problem becomes how to measure the carbon-14. Libby and
fellow chemists at the University of Chicago and other institutions
developed techniques to purify a sample so that it emits no other type of
radiation except for carbon-14, and then run it through a detector
sensitive enough to accurately count the pings emitted by the decay of
single atoms. A newer, faster method developed in the 1970s works by using
a particle accelerator to count the atoms of carbon-14.
Radiocarbon dating can be used on any object that used to be alive. That
includes pieces of animals, people, and plants, but also paper that was
made from reeds, leather made from animal hides, logs that were used to
build houses, and so forth.
The various dating techniques all have limitations. Each works
best for different types of problems. Radiocarbon dating works on organic
materials up to about 60,000 years of age.
Conventional radiocarbon dating requires samples of 10 to 100 grams (0.35
to 3.5 ounces) of an object, depending on the material in question. Newer
forms of dating can use much smaller amounts, down to 20 to 50 milligrams
or 0.0007 to 0.0018 ounces. In both cases, the material is destroyed during
the test.
Radiocarbon samples are also easily contaminated, so to provide accurate
dates, they must be clean and well-preserved. Dirt and other matter must be
washed off with water, but chemical treatments and other cleaning
procedures are also often needed. This is because there are so few atoms to
count; even a little extra carbon from contamination will throw off the
results significantly. A million-year-old sample contaminated by only a
tiny amount of carbon could yield an invalid age of 40,000 years, for
example.
Other dating methods have different strengths. Dendrochronology, also known
as tree-ring dating, depends upon the preservation of certain tree species;
it can extend to about 12,500 years ago for oak trees and to 8,500 years
for bristlecone pine. Potassium-argon dating can date volcanic materials
ranging from less than 100,000 to more than 4 billion years old.
Rubidium-strontium dating can be used to determine the ages of items
ranging from a few million to a few billions of years old; it is widely
used to understand how the Earth and solar system formed and to trace human
migration and trade in archaeology.
Today, the amount of carbon dioxide humans are pumping into Earth’s
atmosphere is threatening to skew the accuracy of this technique for future
archaeologists looking at our own time. That’s because fossil fuels can
shift the radiocarbon age of new organic materials today, making them hard
to distinguish from ancient ones. Thankfully, research published yesterday
in the journal *Environmental Research Letters*
<http://iopscience.iop.org/article/10.1088/1748-9326/11/12/124016> offers a
way to save Libby’s work and revitalize this crucial dating technique:
simply look at another isotope of carbon.
K RAJARAM IRS 20 2 24
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