Methods of Dating The Past

There are four Major Methods of Dating the Past discovered so far that we use to establish a numerical, chronological scale to measure our time here on this planet.

These dating methods establish a chronology for events in the past (relative dates placing events on the timeline in order) as well as absolute dates (which give us quite accurate ages for certain objects, human remains, sites) which help us to further refine our understanding of the timeline.

All of these methods for dating the past have been discovered and applied in an attempt to unravel our own history, to understand the story of humanity. From the first member of our genus homo who emerged in Africa 2.5 Mya until the present, as well as back to the beginnings of life on Earth.

The major methods for dating the past are:

• Historical Records [Today – c.3000 BCE] —
• Dendrochronology [Today — 8000 BCE] —
• Radiocarbon Dating [c.1500 CE – 40,000 BCE] —
• Potassium Argon Dating [250 ka – Beginning] —

In additions there are a handful of other methods which are less developed, precise, and/or less widely applicable.

Dating With Historical Records [Present – c.3100 BCE]

Historical Records exist from c. 3100 BCE until the present. The actual written record of events is limited to the invention of writing and only those cultures who had employed the skill of writing.

The benefit of historical records is that they provide a wealth of detail. More intricate knowledge of human history than all of the other methods combined — by far. The difference between World History versus World Prehistory in this regard cannot be understated.

The downside of the historical record is that it only goes back so far. Writing was invented in Sumer around 3100 BCE, in the ancient city of Uruk, and in Ancient Egypt a few hundred kilometres away at around the same time. Yet it is a stretch to say that our historical record truly goes back this far. The earliest inscriptions that we do have contain quantities of grain, maybe a few names here and there — hardly information of any real historical value. It is probably closer to after 2500 BCE that history truly begins.

So on the one hand, historical records give us astronomically more information (especially in the modern age of social media where the opinions of nearly every human are available to read). On the other hand, this only covers the last 5000 years of history from the birth of the first cities, with the record only pertaining to literature cultures who were able to preserve their knowledge.

Dendrochronology: Tree-Ring Dating [Present – c.8000 BCE]

For each season that trees grow, growth rings form in the trunk, which can be seen in a cross-section of the trunk. One ring for each year, with the thickness of the ring, responding to factors like the quality of the growing seasons. In essence, you can count the tree-rings in a trunk to know a trees age. (The only downside is that you have to cut down the tree to count…)

Annual growth rings of long-lived trees (like sequoias, bristlecone, pines, and European oaks) can be used to date sites in the American southwest, Mediterranean, western Europe, Siberia, and other places. Dendrochronology — as tree-ring dating is formally known — is also used to calibrate radiocarbon dates using sequences of growth rings. [1]

Ancient people used these types of trees for construction, wherever they were available. This method was used originally in the American southwest on the Pueblo Indians. [1]

Radiocarbon Dating [1500 CE – 40,000 BCE]

Radiocarbon dating is a method that measures decay rates of atomic isotope C-14 (Carbon-14) in material, specifically the ratios of C-14, which decay at know rates. Therefore, since the rate of decay is known, depending on the quantity of Carbon-14 — the ratio left — an age can be derived.

C-14 exists in organic samples like wood, hair, charcoal, and bone. Other materials like ivory, paper, seeds grain, straw from mudbrick, and charred food trapped in ancient pottery have all been successfully dated with radiocarbon dating. [2]

When combined with accelerator mass spectrometry (AMS) dates can be produced from miniscule samples. Ideally these dates are then calibrated against tree-ring samples to give a (relatively) precise date in calendar years. [1]

Radiocarbon chronologies are used to date the majority of prehistory after about 40,000 BCE, and is even an excellent tool for refining our chronologies well into the historical era up to about 1500 CE.

Potassium Argon Dating [250 ka – Origins]

Potassium Argon Dating measures the decay rate of 40K atoms that are found in volcanic rocks. [1] Compared to other methods of dating the past (like historical records and dendrochronology) potassium argon dating is particularly useful for older periods.

As such, it helps us to establish a chronology going back from 250,000 years ago (250 ka) back hundreds of millions and billions of years back to the origins of life.

Potassium argon dating is especially useful in places with a high quantity of volcanic rock — such as in East Africa, where many hominin fossils are found in volcanic rock layers. [1]

Other Methods

In addition to Historical Records, Dendrochronology, Radiocarbon Dating, and Potassium Argon Dating there are a few other methods of dating the past which can be used in different circumstances, and in some cases, the technique is improving to the point where they are becoming ever more accurate and reliable. Such as:

• Obsidian Hydration
• Paleomagnetic Dating
• Thermoluminescence
• Uranium Thorium Dating

None of these methods are universally applicable (including the four major methods). Radiocarbon dating, for example, requires living, carbon-based matter situated at the right stratigraphic level under the right conditions to be applied.

Notes

Resources

1. Fagan, Brian M., & Durrani, Nadia. (2017). World Prehistory: A Brief Introduction (Ninth Edition). Routledge. pp. 26-27.
2. Wikipedia Editors. Radiocarbon dating. Wikipedia. <http://en.m.wikipedia.org/wiki/Radiocarbon_dating>. Accessed 10 Dec 2024.