Based on his expertise on ancient documents and biblical genealogies, the Irish Archbishop James Ussher (1581–1656) estimated that our planet was created in the morning of October 23, 4004 BC. Our understanding of world chronology has come a long way since Ussher’s times, thanks to many of the clever dating methods we have developed.

10Linguistic Dating

As time goes by, two geographically isolated communities that speak the same language will display differences in the way they talk. After a few generations, language change becomes more significant. After thousands of years, we’re most likely faced with two related but totally independent languages.

Linguistics can date text on documents, pottery, building walls, and numerous other surfaces. Many important ancient texts have been dated on the basis of linguistic comparison, such as the Zoroastrian Avesta, which is believed to have been written somewhere between 1200–1500 BC based on linguistic similarities with the Indian Vedas.

9Tree-Ring Dating (Dendrochronology)

Most tree species produce new wood each year, resulting in rings of growth that can be easily detected in a cross-section of its trunk. By matching ring sequences from living trees of different ages, it is possible to create a long tree-ring sequence for hundreds, sometimes even thousands of years back in time.

In Alchester, north of Oxford in England, the remains of a Roman fort was uncovered by archaeologists. Thanks to the soil conditions, two large timbers that supported the gate structure survived. Dendrochronological analysis established that both trees were cut between October in the year 44 and March in the year 45, a date consistent with historical data, since the Roman conquest of Britain dates to AD 43.

8Seriation Dating

Many of us can mentally arrange most human creations in a chronological sequence. Archaeologists can do the same with past artifacts. Creations coming from a particular place and time display a distinctive style.

Pottery styles seriation is the foundation of many chronological sequences. Most human cultures later than 8000 BC possess a distinctive ceramic style. In Greece, for example, the Black Figure pottery style (black figures on red background) was dominant from 625 BC until 530 BC, when it became replaced by the Red Figure pottery (red figures on black background). A fragment of Greek Black Figure pottery found in an archaeological context may indicate that the context is no earlier than 625-530 BC.

7Thermoluminescence

Thermoluminescence (TL) can be applied to crystalline materials buried in the ground that have been previously exposed to fire, such as pottery. During a TL test, pottery is heated up, releasing trapped energy in the form of light. This light is measured, revealing the amount of time since the formation of the crystal structure.

From the moment the vessel was fired until the moment it is analyzed, the vessel had been absorbing radiation from the nearby environment. This energy is trapped and accumulated in the pottery’s mineral structure. For an accurate reading, archaeologists have to measure the radiation level at the exact place where the sample was found in the soil. This radiation level is not representative of the radiation level to which the sample was exposed prior to being buried, which is why TL dating has a precision of plus or minus 10 percent and it is often cross referenced with other dating methods.

6Electron Spin Resonance

Like TL, Electron Spin Resonance (ESR) also measures trapped energy. Unlike TL, the ESR test does not heat up the sample, which makes it suitable for materials that decompose when exposed to high temperatures.

ESR is typically used to date tooth samples. Once buried, tooth enamel begins to accumulate energy derived from background radiation. The precision of ESR dating is plus or minus 10–20 percent. Although this figure might seem inaccurate, ESR can provide valuable results for the study of early humans, where we often deal with figures of hundreds of thousands of years.

5Chronologies And Calendars

The dating of the most recent human past used to be largely based on historical chronologies, records and calendars left behind by past civilizations. But ancient calendars tend to run based on a local timekeeping system, normally aligned to a succession of local kings or ruling dynasties. The only way to make these calendars meaningful is to link them with our own calendar.

When two or more of these societies become in touch, we can sometimes find the same events recorded in two independent timekeeping systems, which allows us to align these different calendars. Alexander’s conquest of Egypt in 332 BC, for example, aligns Egyptian and Greek timekeeping systems.

4Cross-Dating

Before modern dating scientific techniques were developed, cross-dating was applied when artifacts from a known sequence coming from a historically dated region was found in areas for which we did not have any reliable chronological information.

While excavating the Palace of Knossos in the Greek island of Crete, several imported Egyptians items dated to 1500 BC were retrieved. This, combined with several examples of Cretan pottery found in Egyptian archaeological contexts of around 1900 BC, allowed archaeologists to extend Egyptian chronology into Crete.

3Radiocarbon Dating

Although the atom of carbon normally has six neutrons in its nucleus (carbon-12), we are surrounded by a small quantity of carbon containing eight neutrons (carbon-14). Carbon-14 is a high energy, unstable atom and tends to decay. The amount of carbon-14 in a given sample will be reduced to half (this is known as half-life) approximately every 5,700 years.

When an organism dies, the exchange of energy and matter stops, and it can no longer incorporate carbon-14 in its tissue. As time goes by, the amount of carbon-14 is reduced, and because we know the rate at which this loss takes place, we can estimate the time elapsed based on the reading of carbon-14 concentration.

This technique can be applied to almost any organic material (human remains, charcoal, plant remains, etc.). One limitation is the age of the sample: Material older than 70,000 years old do not have enough carbon-14 concentration to allow a precise reading. The same happens with samples that are too recent because the concentration of carbon-14 might be too high.

2Potassium-Argon Dating

Radiocarbon dating applied to East African hominin fossils did not produce any results, which suggested the remains of the earliest members of our human evolutionary tree were older than 70,000 years old. Archaeologists sought the help of geologists and a dating method known as Potassium-Argon dating.

Potassium-40 is a radioactive isotope that decays into argon-40, an inert gas. When new volcanic rock is formed, its content of argon-40 is emptied as the gas escapes. Its half-life is about 1.3 billion years. A reading of the relative number of potassium-40 and argon-40 atoms in a volcanic rock sample can be translated into the amount of time elapsed since the formation of the rock.

Many important archaeological sites where early hominins were found are located in areas abundant in volcanic rock. Sometimes, hominin remains are found within a geological layer that can be dated using the potassium-argon technique and some other times they are sandwiched between layers of volcanic rock that can be also dated with this dating method.

1Stratigraphy

As archaeologists conduct an excavation, they expose and study the stratification of the soil (the multiple layers of soil underneath the surface). If no evidence of either human or natural disturbance is found, it is assumed that the underlying layers were deposited prior to the overlying layers.

Stratification only tells us a relative chronological sequence from the earliest bottom layers to the newest archaeological deposits on the top. Some of the material we retrieve from these layers will be suitable for absolute dating. We may find organic material (e.g. bones) suitable for radiocarbon dating or maybe pottery fragments suitable for a Thermoluminescence test. In those cases, we can establish a date for all other items found in the same layer.

When you hear the word library, you probably imagine rows and rows of books. But did you know there are all kinds of libraries dedicated to lending things other than reading materials? From musical instruments to live human beings, you can borrow anything these days if you know where to look!

Related: 10 Lost Libraries And The Mysteries Of Their Contents

10 Tool Library

Ever needed a specific tool for just one project? Enter the tool library, where community members can borrow power drills, hedge trimmers, ladders, and even jackhammers. The first tool library was established in Columbus, OH, in 1976. Today, it lends over 4,800 tools to those who can’t or don’t want to fork out hundreds of dollars for expensive tools they only need once.

Since then, similar services have sprung up around the world to help neighbors share resources and get their projects done. So next time you need a drain snake or a reciprocating saw, try your local tool library!^[1]

Find your nearest tool library!

9 Toy Library

Kids grow up so fast and grow out of their toys even faster. That’s where toy libraries come in—to give old toys new life or even prevent them from being purchased in the first place. Often part of a larger traditional book library, toy libraries allow kids to borrow toys, saving parents cash and keeping a lot of plastic out of landfills.

The oldest continuously operating toy library is in LA County. It was started in 1935by a store owner who noticed kids stealing toys and decided to do something about it: lend them out for free. The program now serves 35,000 children each year, giving them access to the most vital childhood resource: play.^[2]

U.S. readers can find their local toy library or check out the International Toy Library Association.

8 Musical Instrument Library

Want to learn the ukulele? The Musical Instrument Lending Library in Brooklyn has eight you can borrow, along with guitars, cowbells, and steel drums. Another, the “M.I.Brary” in Lafayette, can even hook you up with an accordion! The latter was founded by Dr. Ryan Cazares, who wondered “if there’s a Grammy award winner sitting right here with us, but they don’t even know it because they don’t have the money to purchase an instrument.”

These public services offer anyone the chance to learn a musical instrument or even just try a few to see what sticks, helping make the world a more musical place.^[3]

Many community libraries also offer musical instruments for check-out.

7 Gear Library

Getting outdoors is great for all ages, but camping, hiking, and backpacking gear can add up to hundreds of dollars before you even leave the house. That’s why gear libraries exist to loan equipment to more casual adventurers.

Families in Nature runs one such library in Texas and can kit out at least 100 campers at a time in tents, sleeping pads, backpacks, and headlamps—everything they need to get outside and explore. The Mountaineers’ gear library in Washington even has winter sports equipment like skis. It aims to make outdoor recreation more accessible and inclusive, especially for struggling or underserved communities.^[4]

Gear libraries are a fantastic resource to help get communities outside and enjoy the environment as much as possible!

6 Puzzle Library

If you’ve got a dusty old puzzle sitting in the cupboard, consider donating it to a puzzle library, where jigsaw enthusiasts get their fill. At the online Jigsaw Puzzle Swap Exchange, members have enjoyed over 6100 puzzle swaps. They are able to request specific puzzles or fill out their preferences to receive puzzles that match their interests.

Many puzzle libraries have grassroots origins, like the one Allegra Jabo started in Arlington. Her Douglas Park Little Free Puzzle Library started in her home entryway during the pandemic, where she lends out over 300 puzzles donated by neighbors. She is now looking for a permanent location to house the library. Others operate in private Facebook groups or out of community centers and are always thrilled to welcome new members!^[5]

5 Seed Library

A source of both education and nutrition, in a seed library, gardeners “borrow” seeds at planting time and save a portion of the seeds from the plants they grow to return for future gardeners to use. For many seed libraries, the goal is to preserve local biodiversity by collecting rare and heirloom varieties that are not widely available.

The Global Seed Vault in Svalbard uses thick rock and permafrost to preserve backups of over a million crop seeds varieties, safeguarding the world against the extinction of important food sources—but it is only accessed if disaster strikes. In the meantime, local seed libraries keep varieties in circulation, promoting ongoing evolution as varieties adapt to thrive in the area. Kids can learn where their food comes from, and avid gardeners can help maintain the plant diversity in their neighborhood.^[6]

See the list of seed libraries around the world!

4 Board Game Library

Another popular pandemic pastime, board game libraries provide communities with a fantastic social resource. There are too many games out there for any one family to own them all. Board game libraries can bring together players across different backgrounds and languages (with language-independent games like Qwirkle) to foster a sense of community and cooperation—or just so everyone can gang up on Nanna.

Some game libraries let you take the board games home, while others provide a pay-to-play program onsite and charge an hourly fee. Librarians are even getting clever with 3D printers to replace lost or missing pieces, so the games never have to end!^[7]

3 Sourdough Library

Calling all bakers! The Puratos Sourdough Library in Sankt Vith, Belgium, houses sourdough cultures from all over the world. More than a hundred bakers from over 23 countries contributed samples to this effort to preserve a slice of their heritage. An additional 2,501 starters are registered online, and lab tests of the cultures in Belgium have revealed over 1,400 strains of wild yeast and lactic bacteria!

It was started in 1989 by bakery supply company Puratos, and the collection has continued to rise—pun intended. All samples must come from a spontaneous fermentation (not a commercial starter). The sourdough cultures are kept in mason jars in a carefully controlled environment and refreshed with their original flour every two months to preserve this sourdough heritage for future generations. Dough librarian Karl De Smedt has described the bubbling concoctions as “nothing less than history.” There’s only one sourdough library so far, but you can tour some of the library’s collection virtually.^[8]

2 Human Library

“Don’t judge a book by its cover” has never been more true than at the Human Library or “Menneskebiblioteket” in Copenhagen, Denmark. There, the human “books” are volunteers who come from a stigmatized part of the community, like someone with autism, a naturist, or an extreme body modder. The not-for-profit library offers visitors the opportunity to sit down and dialogue with someone they might not understand. The library hopes to challenge prejudice and foster a more inclusive society.

Since it welcomed over a thousand visitors during its opening week in 2000, The Human Library has expanded activities in over 80 countries around the world. So next time you’re struggling to understand somebody’s perspective, why not borrow them and ask? They’re even developing an app!^[9]

1 Library of Things

Still haven’t found what you’re looking for? Then try a library of things. Part of a global movement to reduce waste and promote a sharing economy, a library of things will keep anything from party supplies to sewing machines.

Libraries of Things exist throughout the world, from the Sharing Depot in Ontario to the Leila in Berlin. Rebecca Trevalyan, the founder of one such library in London, said, “we were students in London, living in tiny houses without much spare space, and not a lot of disposable income… We didn’t need to buy and own sewing machines and drills and lawnmowers and sound systems, but we did need them now and then, and it would be great to be able to access them.”

In this way, libraries of things do more than just save people money: they build a sense of community by creating a pooled resource and letting neighbors share what they need, whether that’s a lawnmower or just a helping hand. These libraries also have an environmental impact, much like many others on this list. No wasted money, nor discarded or leftover items ending up in a landfill.^[10]

Libraries provide vital resources to the communities their serve, and not just in the form of books! Whether you need to borrow a ten-person tent, rainbow carrot seeds, or even a new perspective, there’s bound to be a library that can help you out. Have you visited any of these unusual libraries? Now that you know what’s out there, what will you borrow next?