Love in Your Later Years: 100 Sex and Dating Tips for Seniors
October 29, 2008
Dating among the senior set is becoming more popular thanks to online dating sites for retirees and a more liberal acceptance of senior sexuality. Seniors may have a lot of experience under their belts, but they’re also up for new adventures and relationships. This list of 100 sex and dating tips is just for seniors, from the casual dating crowd to grandmas looking for love.
Getting Back in the Game
Dating again after a divorce, death or just a long slump can be overwhelming. There are new rules to the game, but that doesn’t mean you have to be left out. Check here for tips on getting back on your feet.
No excuses . Don’t cheat yourself of love in your later years by telling yourself that you’re too old or too out-of-date to have a good time. You don’t have to be the cutting edge serial dater you were in your 20s, but that doesn’t mean you don’t have the right to find someone who makes you happy.
Remember how much fun you used to have . Get out of the house and surround yourself with friends and contemporaries when you’re feeling low.
Start off slow . Ease yourself back into dating by attending group events at community centers you’re familiar with.
Don’t overdo it . Staying out all night or all weekend may have been easy back in the day, but keep yourself in check when you’re first starting to date again.
Dating After Loss of a Spouse . Read Elaine Williams’ blog entry about grieving for a spouse and understanding when you’re ready to move on.
Be open minded . The rules may have changed a bit since you were dating, so be open minded about modern dating etiquette .
Stay true to yourself . You’ve kept your morals and your opinions this long, so don’t sacrifice everything you know for a new beau.
Don’t abandon your past . If you’re afraid that a new boyfriend or girlfriend will make you forget your family or past relationships, have a discussion with that person to let them know that you’ll always remain close to your past and that a new relationship doesn’t entail leaving them behind.
Don’t take it so seriously . Getting back in the game can be nerve wracking at first, but just remember to have fun, explore your options and stay true to yourself.
Moving On After a Relationship Break-Up . This article offers more tips for moving on to another relationship after a break-up, divorce or even the death of a loved one.
The Internet is a place many modern singles turn to find dates, including seniors. Read below for safety tips, advice on creating your own profile and more.
100 Top Dating Sites . Find reviews of many different online dating sites here.
Online Dating Safety Tips . Before you create your online profile, consider these safety tips.
Tips to Increase Your Online Dating Success . You’ll find helpful tips in this article, which explains how to set up your profile, picking a photo and more.
SeniorFriendFinder . Consider joining a network like this one, which caters to the over 50 set.
Tips for Writing Your Personal Online Dating Profile . From picking a username to knowing how to flatter yourself, this guide can be very useful when starting an online dating profile.
A Match Made on the Web? . If you’re still not convinced, read this CBS News article about how single seniors are turning to online dating to meet new friends.
Skype . Skype, a video and online telephone service, can keep you connected to your friends and partners around the world. Skype can also be a great tool for getting to know someone you met online without having to commit to a real date.
Meebo . Meebo is another great tool for socializing online with long-distance partners. Meebo is free to use and lets you chat from any computer through your instant message client.
Meetup . Join this social networking group to find out about events and clubs in your area. You can browse by city and/or interest area.
Get a webcam . Sneak a peek at what your online friends really look like when you chat via webcam .
Dating in the 21st Century
Learn all about modern dating rules and etiquette here. Don’t worry, though: not everything’s changed.
What’s a Modern Girl to Do? . Maureen Dowd considers the evolution of courtship and how modern women view relationships in this New York Times article.
The Modern Guy’s Guide to Dating Etiquette . Do single women still like the man to pay for everything or not? Find out how rules like this one have been brought up to date here.
Seniors learning the modern dating game . Seniors can get tips on meeting dates and more in this article.
Dating Etiquette: When to Whip Out Your Wallet . This article considers "old fashion ideas" and new rules for "when it comes to men and money."
Modern Dating Made Easy . This article has tips for identifying red flags and avoiding people who take up too much of your time.
8 Rules for Casual Dating . Are you into the modern idea of casual dating? Find out here.
Places to Meet
At a loss for where to scope out your next date? Read below for our suggestions.
Community center . If you live in an assisted living facility but always stay in your room, venture out into the community center for social interaction.
The gym . The gym is a hot spot for meeting singles, and seniors are no exception. Get to know the people in your swimming or aerobics class to find out if there are any potential matches.
Grandkid’s recital . The next time you attend one of your grandchildren’s recitals or baseball games, check out the other grandparents in attendance. Anyone who’s there will share your passion for family.
Volunteering . This website can help you find a volunteer project in your area to occupy your extra time and connect you to other caring individuals.
Church or temple . Many churches and religious centers sponsor social groups for singles and/or seniors. Sign up to get on their mailing list and attend the next party or trip.
Continuing education class . Learn a new skill like cooking or review a math class you took in college to challenge yourself and meet someone new .
Dance class . From salsa to country western dancing to ballroom, dance class is a great place for people of all ages to get together.
Book club . Start a book club or join an existing one to broaden your social circle and find someone who can satisfy your intellectual curiosity.
Once you’ve found your date, take advantage of senior discounts and other advantages that will open up a new world of dating.
10 Great First Date Ideas . About. com’s Sharon O’Brien lists picnics, dancing and gallery hopping as great first date ideas for seniors.
The theater . It’s well air-conditioned, quiet, and usually offers comfortable seating. You may also be able to afford better seats now than you could in your younger years.
The movies . It sounds cliche, but you probably have way more time for movie dates now than you did when you had to find babysitters and work overtime.
Take a walk . Taking a walk with a date allows you time for conversation, and it gives you the opportunity to fit in a little exercise, too.
Daytime activities . If you like to be in bed early or you have trouble driving in the dark, turn date nights into all-day affairs. You’ll find that museums and movie theaters often offer cheaper rates for daytime visitors, and you can head to popular date locations without the crowds.
Senior citizen vacation . For convenience and safety’s sake, consider taking a vacation with a group of senior citizens. Packages range from the Greek islands to African safaris to weekend getaways in the country.
Romantic Getaway Ideas
As a senior citizen in 2008, you may be the last group of seniors to actually be able to enjoy your retirement and retrieve your Social Security. Take a vacation with your partner a deux or with a whole other group of adventurous retirees.
Caravan Tours . Caravan offers fully escorted tours to places like Costa Rica, New England and the Grand Canyon.
Greek-Holidays. net . Browse this site for special honeymoon packages and golfing vacations in Greece.
SeniorTraveler. com . Learn about hotel, car rental and other vacation discounts for seniors on this website.
ElderTreks. com . The over-50 set can take adventurous "off-the-beaten-path" vacations together through this organization. Destinations include Mongolia, the Antarctic Peninsula, Patagonia and Tanzania.
Smarter Travel Senior Travel . Find travel tips, vacation ideas and more advice for vacationing seniors.
Myrtle Beach . This beach and golfing town is popular with seniors who want to get away without overspending.
New Mexico . New Mexico has a lot to offer senior travelers: romantic sunsets, spas, golf vacations, museums and sightseeing, casinos, hiking and more.
Cruises . Sign up for a seniors-only cruise to explore exotic locations without having to organize everything yourself.
New England . New England Fall Foliage tours are immensely popular and can be a relatively stress-free way to escape.
Savvy Senior Travelers . Rick Steves shares his travel expertise with senior vacationers, from finding accommodating hotels, flights and travel insurance to figuring out where to go.
Sexual Health and Sexuality
Sex in your later years can still be a fulfilling, exiting experience; however, you’ll need to make sure you’re in overall good health to make the most of your sexuality.
The Taboo of Senior Sexuality . ThirdAge explores seniors’ attitudes towards sexuality.
Nine Health Issues That Can Impact Sexual Satisfaction . If you think your sex life is suffering, your overall health might not be in good order. Check these areas to find out.
Senior Sex . From senior sex therapy to Viagra, take a look at how senior sexuality is improving.
Have You Sworn off Dating? . Take this test "to find out just how healthy…your attitude toward dating is."
Sexy Senior Citizens . This piece explores why some seniors are happier with their sexuality than other generations.
Senior Sex: Tips for Older Men . This MSN article has tips for older male partners who want to regain control over their sexuality.
Sex and Aging . This piece encourages seniors to remain positive and research the sexual changes men and women experience as they get older.
HIV/AIDS Cases Growing in U. S. Adults Over 50 . Sexy seniors still need to remember to use protection in order to prevent STDs.
Sex After Menopause . Learn about the changes your body will undergo after menopause and what you can do to stay sexual.
Top 5 Reasons Sex Can Get Better With Age . If you think you’re passed your prime, think again. This list shares the best things about sex in your later years.
Safety Issues for Senior Daters
Unfortunately, there are plenty of scams and gold diggers out there waiting to take advantage of seniors. Learn how to protect yourself here.
Beware of scams . Some dating services and individuals using them prey upon other members to scam them out of money, separate them from their families, or worse.
Gold diggers . Gold diggers work their way into your life through flattery and superficial affection, but all they’re interested in is your savings. Learn how to protect yourself by reading this guide .
Stay grounded . If you haven’t dated in a long time, a new relationship can be exhilarating, but don’t abandon your everyday commitments and responsibilities, like medication, family and paying your bills.
Don’t share personal information to quickly . Just because someone seems sweet, don’t invite him or her into your home or share financial information with them right away, especially if they contacted you for a date.
When you’ve fallen in love again, will you feel like getting remarried or just dating? Consider these tips and articles first.
Some Seniors "Shacking Up" Rather Than Remarrying . This article reports a new trend among seniors who choose not to get remarried because of financial issues.
Senior Marriages . Get an overview of marriage in your later years here.
Divorce and Remarriage . Law for Seniors shares information about how your finances could be affected if you remarry.
Prenuptial Agreements for Seniors . Would a prenup for your second marriage benefit you? Find out here.
Remarriage After Retirement . This article explains how adult children may view their parent’s decision to remarry.
Is It Better to Remarry or Just Live Together? . This article considers things like estate planning, long-term care, Social Security and alimony when making the decision to remarry.
Dating with Illness or Disability
Being in a wheelchair or having an illness doesn’t have to hinder you from dating in your golden years. Read below for tips on dating with a special condition.
Disabled World . This dating service is for disabled and senior citizen singles.
Wheelchair Friendly Holidays . When planning a vacation with your partner, take these tips into consideration if one or both of you will need a wheelchair.
Dating with Breast Cancer . This piece may help you clear up your feelings about dating with a terminal illness.
Disability Sexuality and Dating . If you aren’t used to getting intimate since your disability, read these articles to understand your unique condition a little better.
Dating with Genital Herpes . Even seniors need to use protection: find out what it’s like to date with genital herpes if you don’t.
Talking to Your Family
Help your family get used to the idea of your dating or decision to remarry by considering the following points.
Take it slow . Don’t pressure your new partner and your children to be best friends right away: take the relationship slowly if you notice tension.
Talk to your family . If your family isn’t thrilled with your decision to date again, talk them through the process and help them understand why you’d like to meet new people. Listen to their feelings as well.
Understand that your family might be upset . Your adult children may find it difficult to get used to the idea of your remarrying, especially if your first husband or wife passed away.
How to Get Your Adult Children to Welcome (or even love) Your New Spouse . If you need advice on introducing your adult children to a new boyfriend or girlfriend, read this article.
Dating is always a risk, so don’t ever lose your sense of humor.
Keep yours . Dating as a senior can be nerve racking and full of surprises. Remember to keep your perspective and a sense of humor to make it fun.
Senior Dating: Who Says We Can’t Have Fun? . Check out these jokes and real-life personal ads from seniors.
Senior Sites to Visit
Head to these sites that are full of information and ideas for fun senior living.
Silver Citizen . Get dating tips, as well as plenty of advice and help for decorating, using computers, and more.
Senior Datefinder . If your social circle is small, log on to this site to find a date.
Senior Passions . Senior Passions is another dating site for seniors.
SeniorMatch. com . Singles who are over 50 can log on to this dating website.
AARP Leisure . You can find great vacation and date ideas on this site.
Senior Magazine . The website for this magazine features stories, news and articles about senior law, travel, computer tips, finances and more.
Senior. com . Senior. com is "your Internet community," and you’ll find plenty of ideas for growing relationships, travel and recreation and more.
Education, Jobs and Volunteerism for Seniors . Visit the links on this site to plan out a date or find a way to meet more singles.
Travel and Recreation for Seniors . This government site has tips on traveling and finding discounts.
Articles and Guides
Read these articles and guides for even more tips on romance and sexuality.
Seniors Dating . Learn about health issues, dating services and other seniors dating issues here.
Senior Dating . Suite 101 writer Cherie Burbach has great tips for "finding love after 50."
Suddenly Single Seniors and Dating . This article helps seniors get used to modern dating strategies like creating online profiles.
Ask April Advice for Retirees, Boomers, Seniors . April dishes up lots of dating tips and etiquette here.
How to Overcome First Date Anxiety . This helpful article is targeted at senior daters.
Senior Romance: Finding Love in Your Later Years . Get tips for planning a stress-free first date, finding singles and more from this piece.
Seniors and Sex . Learn about senior sexual oppression and how it hurts our aging population.
Senior Sex: Romance, Act Two . Canada. com’s article shares tips for spicing up your sex life despite the unique intimacy challenges you may face as you age.
Back in the Game: Smart Senior Dating Tips . You’ll find very helpful tips for figuring out what you want out of dating, managing a dating service account and more.
Senior Dating Interview: Dr. Helen Fisher . Dr. Helen Fisher, a biological anthropologist and member of the anthropology department of Rutgers University, discusses how the concept of senior dating has changed and doles out advice to seniors interested in dating again.
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Age of the Earth
The age of the Earth is 4.54 ± 0.05 billion years (4.54 ? 10 9 years ± 1%). [ 1 ] [ 2 ] [ 3 ] This age is based on evidence from radiometric age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples .
Following the scientific revolution and the development of radiometric age dating, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. [ 4 ] The oldest such minerals analyzed to date – small crystals of zircon from the Jack Hills of Western Australia – are at least 4.404 billion years old. [ 5 ] [ 6 ] [ 7 ] Comparing the mass and luminosity of the Sun to those of other stars. it appears that the solar system cannot be much older than those rocks. Calcium-aluminium-rich inclusions – the oldest known solid constituents within meteorites that are formed within the solar system – are 4.567 billion years old, [ 8 ] [ 9 ] giving an age for the solar system and an upper limit for the age of Earth .
It is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites. Because the exact amount of time this accretion process took is not yet known, and the predictions from different accretion models range from a few millions up to about 100 million years, the exact age of Earth is difficult to determine. It is also difficult to determine the exact age of the oldest rocks on Earth, exposed at the surface, as they are aggregates of minerals of possibly different ages.
Radiocarbon dating
From Wikipedia, the free encyclopedia
Radiocarbon dating is a method of determining the age of an object by using the properties of radiocarbon. a radioactive isotope of carbon. The method was invented by Willard Libby in the late 1940s and soon became a standard tool for archaeologists. It depends on the fact that radiocarbon, often abbreviated as 14
C. is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide. This is then incorporated into plants by photosynthesis. and animals acquire 14
C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and from that point the amount of 14
C it contains begins to reduce as the 14
C undergoes radioactive decay. Measuring the amount of 14
C in a sample from a dead plant or animal such as piece of old wood or a fragment of bone provides information that can be used to calculate when the animal or plant died. The oldest dates that can be reliably measured by radiocarbon dating are around 50,000 years ago, though special preparation methods occasionally permit dating of older samples.
While the idea behind radiocarbon dating is straightforward, years of additional work were required to develop the technique to the point where accurate dates could be obtained. Research has been going on since the 1960s to determine what the proportion of 14
C in the atmosphere has been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's actual calendar age. In addition to this curve, other corrections must be made to account for different proportions of 14
C in different types of organism (fractionation) and different 14
C levels in different parts of the biosphere (reservoir effects).
Measurement of radiocarbon was originally done by beta-counting devices, so called because they counted the amount of beta radiation emitted by decaying 14
C atoms in a sample. More recently, accelerator mass spectrometry has become the method of choice; it can be used with much smaller samples (as small as individual plant seeds), and gives results much more quickly.
The development of radiocarbon dating has had a profound impact on archaeology. In addition to permitting more accurate dating within archaeological sites than did methods previously in use, it also allows comparison of dates of events across great distances. Histories of archaeology often refer to the early impact of the new method as the “radiocarbon revolution”. Occasionally, the method is used for items of popular interest such as the Shroud of Turin. which is claimed to show an image of the body of Jesus Christ. A sample of linen from the shroud was tested in 1988 and found to date from the 1200s or 1300s, casting doubt on its authenticity.
Contents
Background [ edit ]
History [ edit ]
In the early 1930s Willard Libby was a chemistry student at the University of Berkeley. receiving his Ph. D. in 1933. He remained there as an instructor until the end of the decade. In 1939 the Radiation Laboratory at Berkeley began experiments to determine if any of the elements common in organic matter had isotopes with half-lives long enough to be of value in biomedical research. It was soon discovered that 14
C 's half-life was far longer than had been previously thought, and in 1940 this was followed by proof that the interaction of slow neutrons with 14
N was the main pathway by which 14
C was created. It had previously been thought 14
C would be more likely to be created by deuterons interacting with 13
C. At about this time Libby read a paper by W. E. Danforth and S. A. Korff, published in 1939, which predicted the creation of 14
C in the atmosphere by neutrons from cosmic rays which had been slowed down by collisions with molecules of atmospheric gas. It was this paper that first gave Libby the idea that radiocarbon dating might be possible. [ 1 ]
In 1945, Libby moved to the University of Chicago. He published a paper in 1946 in which he proposed that the carbon in living matter might include 14
C as well as non-radioactive carbon. [ 2 ] [ 3 ] Libby and several collaborators proceeded to experiment with methane collected from sewage works in Baltimore, and after isotopically enriching their samples they were able to demonstrate that they contained radioactive 14
C. By contrast, methane created from petroleum had no radiocarbon activity. The results were summarized in a paper in Science in 1947, and the authors commented that their results implied it would be possible to date materials containing carbon of organic origin. [ 2 ] [ 4 ]
Libby and James Arnold proceeded to experiment with samples of wood of known age. For example, two wood samples taken from the tombs of two Egyptian kings, Zoser and Sneferu. independently dated to 2625 BC plus or minus 75 years, were dated by radiocarbon measurement to an average of 2800 BC plus or minus 250 years. These results were published in Science in 1949. [ 5 ] [ 6 ] In 1960, Libby was awarded the Nobel Prize in Chemistry for this work. [ 2 ]
Physical and chemical details [ edit ]
In nature, carbon exists as two stable, nonradioactive isotopes. carbon-12 ( 12
C ), and a radioactive isotope, carbon-14 ( 14
C ), also known as "radiocarbon". The half-life of 14
C (the time it takes for half of a given amount of 14
C to decay ) is about 5,730 years, so its concentration in the atmosphere might be expected to reduce over thousands of years. However, 14
C is constantly being produced in the lower stratosphere and upper troposphere by cosmic rays. which generate neutrons that in turn create 14
C when they strike nitrogen-14 ( 14
N ) atoms. [ 2 ] The 14
C creation process is described by the following nuclear reaction :
Once produced, the 14
C quickly combines with the oxygen in the atmosphere to form carbon dioxide ( CO
2 ). Carbon dioxide produced in this way diffuses in the atmosphere, is dissolved in the ocean, and is taken up by plants via photosynthesis. Animals eat the plants, and ultimately the radiocarbon is distributed throughout the biosphere. The ratio of 14
Principles [ edit ]
During its life, a plant or animal is exchanging carbon with its surroundings, so the carbon it contains will have the same proportion of 14
C as the biosphere and the carbon exchange reservoir. Once it dies, it ceases to acquire 14
C. but the 14
C within its biological material at that time will continue to decay, and so the ratio of 14
C to 12
C in its remains will gradually reduce. Because 14
C decays at a known rate, the proportion of radiocarbon can be used to determine how long it has been since a given sample stopped exchanging carbon—the older the sample, the less 14
C will be left. [ 8 ]
The equation governing the decay of a radioactive isotope is: [ 2 ]
where N 0 is the number of atoms of the isotope in the original sample (at time t = 0, when the organism from which the sample was taken died), and N is the number of atoms left after time t . [ 2 ] ? is a constant that depends on the particular isotope; for a given isotope it is equal to the reciprocal of the mean-life — i. e. the average or expected time a given atom will survive before undergoing radioactive decay. [ 2 ] The mean-life, denoted by ? . of 14
C is 8,267 years, so the equation above can be rewritten as: [ 11 ]
The sample is assumed to have originally had the same 14
C / 12
C ratio as the ratio in the biosphere, and since the size of the sample is known, the total number of atoms in the sample can be calculated, yielding N 0 . the number of 14
C atoms in the original sample. Measurement of N . the number of 14
C atoms currently in the sample, allows the calculation of t . the age of the sample, using the equation above. [ 8 ]
The half-life of a radioactive isotope (the time it takes for half of the sample to decay, usually denoted by t 1/2 ) is a more familiar concept than the mean-life, so although the equations above are expressed in terms of the mean-life, it is more usual to quote the value of 14
C 's half-life than its mean-life. [ note 1 ] The currently accepted value for the half-life of 14
C is 5,730 years. [ 2 ] This means that after 5,730 years, only half of the initial 14
C will have remained; a quarter will have remained after 11,460 years; an eighth after 17,190 years; and so on.
The above calculations make several assumptions, such as that the level of 14
C in the biosphere has remained constant over time. [ 2 ] In fact, the level of 14
C in the biosphere has varied significantly and as a result the values provided by the equation above have to be corrected by using data from other sources in the form of a calibration curve, which is described in more detail below. [ 12 ] For over a decade after Libby's initial work, the accepted value of the half-life for 14
C was 5,568 years; this was improved in the early 1960s to 5,730 years, which meant that many calculated dates in published papers were now incorrect (the error is about 3%). However, it is possible to incorporate a correction for the half-life value into the calibration curve, and so it has become standard practice to quote measured radiocarbon dates in "radiocarbon years", meaning that the dates are calculated using Libby's half-life value and have not been calibrated. [ 13 ] [ note 2 ] This approach has the advantage of maintaining consistency with the early papers, and also avoids the risk of a double correction for the Libby half-life value. [ 15 ]
Carbon exchange reservoir [ edit ]
Simplified version of the carbon exchange reservoir, showing proportions of carbon and relative activity of the 14
The different elements of the carbon exchange reservoir vary in how much carbon they store, and in how long it takes for the 14
C generated by cosmic rays to fully mix with them. [ 2 ] The atmosphere, which is where 14
C is generated, contains about 1.9% of the total carbon in the reservoirs, and the 14
C it contains mixes in less than seven years. [ 16 ] [ 17 ] The ratio of 14
C to 12
C in the atmosphere is taken as the baseline for the other reservoirs: if another reservoir has a lower ratio of 14
C to 12
C. it indicates that the carbon is older and hence that some of the 14
C has decayed. [ 12 ] The ocean surface is an example: it contains 2.4% of the carbon in the exchange reservoir, [ 16 ] but there is only about 95% as much 14
C as would be expected if the ratio were the same as in the atmosphere. [ 2 ] The time it takes for carbon from the atmosphere to mix with the surface ocean is only a few years, [ 18 ] but the surface waters also receive water from the deep ocean, which has over 90% of the carbon in the reservoir. [ 12 ] Water in the deep ocean takes about 1,000 years to circulate back through surface waters, and so the surface waters contain a combination of older water, with depleted 14
C. and water recently at the surface, with 14
C in equilibrium with the atmosphere. [ 12 ]
Creatures living at the ocean surface have the same 14
C ratios as the water they live in, and as a result of the reduced 14
C / 12
C ratio, the radiocarbon age of marine life is typically about 400 years. [ 19 ] [ note 4 ] Organisms on land, however, are in closer equilibrium with the atmosphere and have the same 14
C / 12
C ratio as the atmosphere. [ 2 ] These organisms contain about 1.3% of the carbon in the reservoir; sea organisms have a mass of less than 1% of those on land and are not shown on the diagram. [ 16 ] Accumulated dead organic matter, of both plants and animals, exceeds the mass of the biosphere by a factor of nearly 3, and since this matter is no longer exchanging carbon with its environment, it has a 14
C / 12
Dating considerations [ edit ]
The variation in the 14
C / 12
C ratio in different parts of the carbon exchange reservoir means that a straightforward calculation of the age of a sample based on the amount of 14
C it contains will often give an incorrect result. There are several other possible sources of error that need to be considered. The errors are of four general types:
variations in the 14
C / 12
C ratio in the atmosphere, both geographically and over time;
isotopic fractionation;
variations in the 14
C / 12
C ratio in different parts of the reservoir;
contamination.
Atmospheric variation [ edit ]
In the early years of using the technique, it was understood that it depended on the atmospheric 14
C / 12
C ratio having remained the same over the preceding few thousand years. To verify the accuracy of the method, several artefacts that were datable by other techniques were tested; the results of the testing were in reasonable agreement with the true ages of the objects. However, in 1958, Hessel de Vries was able to demonstrate that the 14
C / 12
C ratio had changed over time by testing wood samples of known ages and showing there was a significant deviation from the expected ratio. This discrepancy, often called the de Vries effect, was resolved by the study of tree rings. [ 20 ] [ 21 ] Comparison of overlapping series of tree rings allowed the construction of a continuous sequence of tree-ring data that spanned 8,000 years. [ 20 ] (Since that time the tree-ring data series has been extended to 13,900 years.) [ 22 ] Carbon-dating the wood from the tree rings themselves provided the check needed on the atmospheric 14
C / 12
C ratio: with a sample of known date, and a measurement of the value of N (the number of atoms of 14
C remaining in the sample), the carbon-dating equation allows the calculation of N 0 – the number of atoms of 14
C in the sample at the time the tree ring was formed – and hence the 14
C / 12
C ratio in the atmosphere at that time. [ 20 ] Armed with the results of carbon-dating the tree rings, it became possible to construct calibration curves designed to correct the errors caused by the variation over time in the 14
C / 12
C ratio. [ 23 ] These curves are described in more detail below .
Atmospheric 14
C. New Zealand [ 24 ] and Austria. [ 25 ] The New Zealand curve is representative of the Southern Hemisphere; the Austrian curve is representative of the Northern Hemisphere. Atmospheric nuclear weapon tests almost doubled the concentration of 14
C in the Northern Hemisphere. [ 9 ] The date that the Partial Test Ban Treaty (PTBT) went into effect is marked on the graph.
Coal and oil began to be burned in large quantities during the 1800s. Both coal and oil are sufficiently old that they contain little detectable 14
C and, as a result, the CO
2 released substantially diluted the atmospheric 14
C / 12
C ratio. Dating an object from the early 20th century hence gives an apparent date older than the true date. For the same reason, 14
C concentrations in the neighbourhood of large cities are lower than the atmospheric average. This fossil fuel effect (also known as the Suess effect, after Hans Suess. who first reported it in 1955) would only amount to a reduction of 0.2% in 14
C activity if the additional carbon from fossil fuels were distributed throughout the carbon exchange reservoir, but because of the long delay in mixing with the deep ocean, the actual effect is a 3% reduction. [ 20 ] [ 26 ]
A much larger effect comes from above-ground nuclear testing, which released large numbers of neutrons and created 14
C. From about 1950 until 1963, when atmospheric nuclear testing was banned, it is estimated that several tonnes of 14
C were created. If all this extra 14
C had immediately been spread across the entire carbon exchange reservoir, it would have led to an increase in the 14
C / 12
C ratio of only a few per cent, but the immediate effect was to almost double the amount of 14
C in the atmosphere, with the peak level occurring in about 1965. The level has since dropped, as the "bomb carbon" (as it is sometimes called) percolates into the rest of the reservoir. [ 20 ] [ 26 ] [ 27 ]
Isotopic fractionation [ edit ]
Photosynthesis is the primary process by which carbon moves from the atmosphere into living things. In both photosynthetic pathways (C3 and C4 ) 12
C is absorbed slightly more easily than 13
C. which in turn is more easily absorbed than 14
C ratios in plants that differ from the ratios in the atmosphere. This effect is known as isotopic fractionation. [ 28 ] [ 29 ]
To determine the degree of fractionation that takes place in a given plant, the amounts of both 12
C and 13
C isotopes are measured, and the resulting 13
C / 12
C ratio is then compared to a standard ratio known as PDB. [ note 5 ] The 13
C / 12
C ratio is used instead of 14
C / 12
C because the former is much easier to measure, and the latter can be easily derived: the depletion of 13
C relative to 12
C is proportional to the difference in the atomic masses of the two isotopes, so the depletion for 14
C is twice the depletion of 13
C. [ 12 ] The fractionation of 13
C. known as ? 13 C. is calculated as follows: [ 28 ]
where the ‰ sign indicates parts per thousand. [ 28 ] Because the PDB standard contains an unusually high proportion of 13
C. [ note 6 ] most measured ? 13 C values are negative.
