Scientist don't believe that man came from Christ but they still use the term B.c., even though they say they don't believe in Christ.

1. Nobody believes "that man came from Christ." That's not any sort of Christian position (although Mormons might believe something similar, as I understand the Mormon faith). And whether you think human evolution is true or not has little or nothing to do with the Christian understanding of the role of the Christ.

   I'm sorry I can't give references on an elementary-school level, but two good ones are

   • God After Darwin: a Theology of Evolution, by John Haught, attempts to enunciate a theology that takes both Christianity and evolution seriously.
   • Can a Darwinian be a Christian? by Michael Ruse. The author, a well-respected philosopher of biology and (so far as I know) an atheist, concludes that the answer is yes.

2. Whether you are Christian or not has nothing to do with whether Jesus of Nazareth was a real person. I can't see how any Christian could think he didn't exist, but atheism and other non-Christian beliefs do not, as such, deny the historical existance of Jesus. (What they deny is the Christian claim about who Jesus was.) See this MadSci answer for more. Jesus of Nazareth is, it would seem, as convenient a person as any to whom to refer dates.

3. Actually, Jesus of Nazareth is not a terribly convenient person to whom to refer dates, because his dates of birth and death cannot be established with precision. Furthermore, we refer dates to what we now know to be not the year of his birth--best current estimates are between 7 and 4 B.C.

   We do this because the common Western system of dating was established when the Christian Church was intellectually dominant in the West, and a respected historian of the time decided that Jesus was born in the 753d Year from the Founding of Rome. See this MadSci answer for more.

4. Many people, Christian or not, use A.D. (anno domini, "in the year of [our] Lord") and B.C. ("before Christ") for convenience, because dates have to be referred to something.

   In most historical disciplines and in most countries around the world, the Western system of dates is used because something has to be the default world dating system. But for the past half century or so it's often been called "the Common Era," and dates are called C.E. and B.C.E. ("before the Common Era") to remove the reference to Christ. See this MadSci answer for more.

   Astronomers use so-called Julian dates, which are days and fractions of days, numbered from Julian Day Zero: 12:00 noon GMT on January 1, 4713 B.C. This reference was presumably chosen so that all recorded astronomical observations would have a positive Julian Date.

   My daughter's next birthday (April 11, 2001) is Julian Day 2,452,011; she was born at about Julian Date 2,447,628.145. Here's a calculator which will convert Universal Time (GMT) into the Julian Date.

Anyway, who told you that scientists don't believe in Christ? The proportion of Christians among the general run of scientists is, in the United States at least, similar to, or only slightly lower than, the proportion of Christians among the population at large. See this MadSci answer for more.