Please reread pg. xxix in the textbook, beginning with the second paragraph.  You can see how difficult it is for historians and others to agree on the best, or even a common, method of measuring and identifying time.  But is certainly is important to try.

In this class we will use, for the most ancient times, the new term BP, which stands for "Before the Present Time" - actually 1950.  Then for the periods from the rise of human civilizations, we will use BCE and CE.  The text's authors discuss this in the fourth and fifth paragraphs on page xxix.

Of course we all know what a "year" is - or do we?  Humans have developed over time at least two types of "year":  one that is equal to the time that it takes the earth to revolve around the sun.  This we call a "solar" year, and is the one used in countries and societies in which Christianity has been dominant.  A second "year" is equal to the time that it takes the moon, observed from earth, to move through its "phases", that is from full moon to full moon, multiplied by 12.  This we call a "lunar" year, and is the one used in countries and societies located nearer the equator - and over time, those societies in which Judaism and Islam have been dominant.

Obviously these two years are different in terms of length.  The solar year is about 365 days long; the lunar year is about 354 days long..

Whichever of these years one uses in measuring the past will not be meaningful for that long period of the universe's history before the sun and the earth emerged.  But astronomers and scientific historians use "year", or more likely billions of "years" to identify long time spans in the distant past of the universe's history.

It is only in the very recent past that scientists and astronomers have been able to trace the early history of the universe, and they continue to push back its beginning, in what many call the "Big Bang", further and further BP.  Most, however, do agree now on the age of the earth in general terms, and on the historical period in which humans first appeared.

Before the invention of writing, and with it, the production of written sources which historians can use today in their research, it is very difficult to determine actual dates or even more generally time periods without using newly developed scientific methods.  One of the most useful is called "radio-carbon dating".  Jared Diamond, in his book Guns, Germs, and Steel, provides an excellent definition of this important scientific and historical tool.

For those of you who are interested in and knowledgeable about science, click on formulas for both Carbon 14 and K-Argon dating.  [note to designer - this link and the one above should appear in "b", upper right]

We will return to a discussion of "time" from time to time! during this course.