The dating system used in the Signposts is usually the same as that we use today (in early 21st century USAmerica), in order to make the chronology clearer to readers. However, the actual calendaring system used by future peoples may be radically different, for a multitude of reasons. The seachanges in regard to religious beliefs may move our present system based on the life of Christ (BC, AD) to another framework entirely, for example. Our exodus from Realtime to virtual time may also bring about big changes in our calendaring methods (as one virtual year might be equivalent to a hundred or thousand Realtime years). If exotic and fanciful technologies like relativistic-effect drives and/or time travel become realized and put to active use by civilization, those too could change date reference systems in a big way.
Another date issue is the lack of precise dates given here for some developments or events. Though I have attempted to provide 'hard' dates where possible, many items simply cannot be quantified that way, due to the huge number of variables involved. Ergo, the heavy use of time 'ranges' rather than precise years.
So what about more details on the mainstream dating system itself? Glad you asked! It's surprisingly convoluted in some ways, as well as driven by one particular world religion (since western nations have dominated world history for the last few millennia).
Dates given with the acronym BC mean Before Christ, while those with AD refer to the Latin "Anno Domini", meaning after Christ.
Here's an example of usage: Say we're writing about some event during the Ice Age, some 19,000 years ago. If the present year is 2000 AD, then you must subtract 2000 years from 19,000 to get the BC date, which would be 17,000 BC.
Also, BC dates run backwards, like the countdown to a rocket launch, while AD dates run forward, like more typical counting procedures. That is, 10,000 BC is actually later than 11,000 BC.
To add to the acronyms, some scholars use B.C.E., which means Before the Common Era, rather than BC, and C.E. (Common Era) for AD.
But don't think the acronyms end there. B.P. was added to the mix in the 1950s by some researchers as a reference related to early carbon dating of fossils and artifacts. B.P. stands for Before Present, where the present is, logically enough, 1950. Huh? Yeah, 1950. That's no typo. So 50 BP is actually 1900 AD. Are things getting weird enough for you yet? Just wait. it gets worse.
[jump off sources include...Outdated? B.C., A.D. are history By Maria Titze, Deseret News staff writer, February 04, 2000]
Of course, BC, BCE, and BP don't matter in the future history portions of the timeline-- but they do in the sections dealing with the past. BC and BCE are interchangeable, but BP, as you may have noticed above, can really throw dates into chaos. Fortunately for you, you won't encounter BP very often in literature. Unfortunately for me, on rare occasion I do. And for a while I was off-base on the exact meaning of BP when I was referencing dates. This wasn't entirely my fault, as an amazing number and variety of dictionaries and scientific reference books don't even list or fully define B.P. in their pages. I know, for I looked. I also don't recall BP being explained to me at any time during my high school or college educations. Of course, it is a somewhat arcane convention, after all.
After consulting somewhere between a half dozen and a dozen reference books on the subject and finding no adequate separate definition or formula for BP, I concluded (erroneously) that it too was equivalent to BC or BCE, or else close to it.
For this reason there may be a handful of dates in those sections of the Signposts dealing with the past where I mistakenly treated BP and BC as interchangeable. This means there may be something like a half dozen past dates in the Signposts which are off by some number of centuries. Luckily, this represents only a tiny fraction of one percent of dates in the Signposts (since I rarely encountered BP in past research), and will likely be entirely corrected over time as I update the material with fresh citations and estimates. I can't simply go back and adjust the dates because I no longer have copies of the original articles to which to refer. Too, as I usually mistakenly adjusted the acronym from BP to BC for consistency's sake, I don't know which specific half dozen citations originally hosted BP dating.
So I'll just correct these over time in general, with further research. In the meantime though, I badly need to pin down the definition of BP to make sure such errors never mount to significant proportions in the future.
I finally found some information regarding BP on the net-- but darn if it didn't raise more questions than it answered. First off, the radiocarbon dating on which BP is based is usually only a fuzzy estimate of a date, rather than a concrete number. So the actual date might be a few centuries or so different from the time indicated by the radiocarbon technique from which BP springs. Overall, the older the actual age of an object, the greater the error that might accrue in the carbon-dating of same.
Radiocarbon dating accuracy has been increased in recent decades with calibration based on tree ring data and deep sea coral, which helps compensate for the errors that solar and magnetic fluctuation over millennia brings to the count.
As calibration significantly increases the accuracy of carbon dating, scientists have taken to using the acronyms BC/AD and BP as a way of distinguishing between calibrated and non-calibrated carbon dates. If a date is calibrated, BC or AD is used as appropriate. If it is not calibrated (and therefore likely less accurate), BP is used. A less often used alternative to mark uncalibrated dates is to refer to them as "historic" years bc or ad (lowercase letters) with calibrated dates using uppercase (BC and AD).
Too, radiocarbon dating doesn't work well for ages less than around 300 years, for several reasons, including large fluctuations in solar activity in the 17th century, massive human burning of fossil fuels during the 19th century, and numerous nuclear explosions in the latter half of the 20th century, which all affected the carbon-14 in the biosphere on which radiocarbon dating depends.
The techniques of radiocarbon dating work more or less reliably for at least as far in the past as 40,000-50,000 years, and may eventually do so for twice that far. Alternate dating techniques such as Potassium-Argon and Fission-Track dating, Thermoluminescence, and others, are available for cases where radiocarbon dating is inadequate.
[jump off sources include...Dating techniques in archaeology]
Frustratingly, my research gave me no easy and straightforward way to convert raw BP dates into accurate BC or AD numbers. Indeed, it appears that often only the researchers in possession of all related raw data may do so, rather than a remote reader of their usually incomplete abstracts, like me.
But then again, a general rule of thumb regarding the conversion of BP dates to BC or AD might be derived. The resulting dates may be off by decades or even centuries at times, but since we'll typically only be using BP-based numbers for dates of 10,000 BC or before, the margin of error will be acceptable for most purposes. Here's my rule of thumb procedure for the Signposts in this regard:
#1: Add the number required to update the BP number. For instance, if the current year is 2000, subtract 1950 from 2000 to get 50. Then add 50 to the BP number to get a more accurate absolute number of years from the present.
#2: Now, is the resulting number from above greater than the current year being reported in your computer's date/time functions? If greater, then you'll want to use BC. If it's less, you'll want AD.
Example A: Assume you have 15,000 BP after the adjustments described above. It's greater than the current year of 2000. So you'll want BC. Subtract the current year from the adjusted BP number (in this example you get 13,000). Tack on BC. And viola! 13,000 BC!
Example B: Assume you have 450 BP after the adjustments described in rule #1 above. It's less than the current year of 2000. So you'll want AD. Subtract the adjusted BP number from the current year (in this example you get 1550). And you end up with 1550 AD.
#3: Lastly, always preface the final date you with the word "approximately". Because that's what BP is.
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