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Sating of mocksy Richard J ottomley

ew things on earth are so underrated as rocks. They seem sodull. Yet from rocks we create the metals and materials used forhorne and industry. Rock is the source of petroleum, which makes

modern transportation and plastics possible, and the dominant factor in theshape of the natural world around us. But more fasci-nating than any of these insights is the fact that rocks canspeak to us-not in the English language, of course, butthey speak nonetheless. Every rock is like a miniature black-boxflight recorder that can be examined in a lab. There it can reveal suchthings as what temperatures and pressures it has seen, the direction of thenorth pole when it was formed, often the climate in which it was createdand, most surprisingly, how old it is.

Let's consider why rocks have different ages. Why don't they all haveone age that reflects the time of their creation? The answer to this is thatnatural processes like wind and water eat away at rock and reduce it to sandand mud, which eventually drain to the sea. There they become depositedand glued together again into new rocks called sandstone and shale. Newcarbonate rock such as limestone can also be created by reef-buildingorganisms in the sea. Other processes such as metamorphism and volcanismalso create new rock. This new rock often remembers only the age of itslatest reincarnation.

I would like to explain how simple it is to date a rock. This techniqueis not cloaked in mystery. The fact that we can do this is a result of God'snatural laws, the master plan by which he structured the universe. Every-thing we can see in the earth or universe can be described by four basicforces. You are already quite familiar with the gravitational force, whichholds you down, and the electromagnetic force shown in phenomena such aslight and chemistry. The other two forces, the strong and weak nuclearforces, are not as easily observed in everyday life. The sun is an example ofan environment where strong and weak forces predominate. t is an as-tounding and yet humbling thought that with these four forces, the wholeuniverse as we know it can be described-clearly a tribute to the creativegenius of God.

One of the results of the interactions of these forces is the periodictable (Fig. 1 we all remember from high school chemistry that describeshow the different elements relate to each other. You will remember that an

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2 3 5 6 7 9 . 11 12 13 ,. 15 ,. 17 ---d ;-, ,H He:(7) , , .=..,.., - - "'- - -atom is a dense central coremade up of particles calledneutrons and protons, and that acloud of electrons circles thenucleus. The number of elec-trons equals the number ofprotons for anyone species ofatom. The periodic table is amanifestation of the basicstructure of matter. Start withhydrogen, the lightest element,then keep adding protons andneutrons to make up successivelyheavier atoms. For the momentlet's ignore neutrons. If you addone proton to hydrogen you gethelium. You can keep addingprotons until you have a nucleuswith eighty-three protons. This

3 , .tornlenumbGr , . , . ,Li Be element symbol B C N 0 F Ne9012182(3) 1991-..;0 "",,,,,_m"" 101\11 Il.OH ? \.0IlE7 ,,- ,,-- ....... ,.,.. "" - - 13Na Mg AI Si P S CI Ar

,.,..;; 3097376' n ,- - - _. - ":' - - .... . . . . . . " - N - "'i.'.. '" 30 35K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr, 50.9415(1) 5 '_ ' l f rJ --.. MO .. .- , n '" n n , a- "';;" - ... ,- ': - - .... , -7Rb Sr Y Zr Nb Mo Tc Ru Rh Pd f:-g Cd In Sn Sb Te I Xe . =' 10107(2) ,OIU 1 U.81 1'871 121.7 , ' 121 190447-- - ..... ...... .., - --s 5770Cs Ba * Lu Hf Ta W Re Os Ir Pt Au ,ttg TI Pb Bi Po At Rn'u 137.m 118. ,80\1011 ' n8411) l 1 m 11iS01 a 207.21 =- --- - - - 7 89-102 ' 04 '" 70 ' . OS ' ' ' ' 'Fr Ra ** Lr Rf Db Sg Bh Hs Mt Uun Uuu Uub Uuq Uuh Uuo., "''' 12e3.11 15 "'"'''' "'" "'" "'" "'" L---: --- L l-=---- - -- - -- -- - 758 59 63 58 67 59*Ianthanides La Ce Pr Nd Pm Sm Eu Gd Tb Ho Er Tm Yb'"'''''''' ':;:' = """ ' ' ' .912 ' I '572 ,e.t\I3032 ' ..,.. ., "';Z"" - - - ,........ - .. 67 .. ' ' '**actinides Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No

mm n ... =0,.,,, Uoe,4 " m. - Il.1011Fig. 1. The Periodic Table of Elements

is the element bismuth. If you add one more proton,something rather surpri sing happens. The element youform with atomic number eighty-four (polonium) isradioactive I t doesn't want to stick together. If youleave it long enough it will decay into other nonradioac-tive elements. It is unstable--the nuclear glue is nolonger strong enough to hold the nucleus together andthus it decays. This explains why there isn't an infinitenumber of chemical elements. All nine natural elementsheavier than bismuth are also radioactive and decay.Humans have tried for over forty years to glue heavierelements together, but each one is radioactive andeventually decays to lighter elements. Thus we see thatradioactivity is a natural phenomenon tied to the funda-mental structure of matter. I t is related to the strongand weak nuclear forces and is not an independentphysical quantity that can be varied at will; it comesabout when the nuclear glue is no longer strong enoughto hold a particular nucleus together. Because it is anuclear process, virtually nothing we can do externallycan affect the process. Heat, pressure, electricity, andexplosions all involve the electrons of an atom, not thenucleus.

In a simple radioactive decay, we call the radioac-tive atom the "parent atom" and the stable atom thatresults the "daughter atom." The rate of transformationfrom parent to daughter is constant for any particularradioactive nucleus. Every radioactive atom has a charac-teristic half-life. The half-life is simply how long it takesfor one-half the radioactive atoms to decay Someradioactive atoms have half-lives of billionths of asecond while others have half-lives of billions of years.

The term "decay constant" is related to half-life and issimply a measure of the probability that an atom willdisintegrate in a unit of time.

Because the decay rate of radioactive atoms isconstant, we can use it to tell time in the same way thatthe constant movement of hands of a clock enables usto tell time. Even a small piece of rock contains trillionsof atoms, some of which are naturally radioactive.Throughout the life of this rock these radioactive parentatoms decay into daughter isotopes at a steady, predict-able rate. If we count the parent and daughter atoms, wecan tell how old the rock is.

Let's demonstrate how this can be done. Think ofa rock as a box made up of golf balls of different colors,each color representing a different type of atom such asiron or silicon. Assume that the box contains onehundred radioactive white golf balls and that they decayat a rate of one ball per year. Every time one decays itturns green. I can come back anytime during the nexthundred years and tell how much time has passed simplyby noting how many golf balls have turned green. Ifthere are seventy-five white balls and twenty-five greenballs, we know that twenty-five years have passed. Inthis simple situation we could tell the amount of timethat passed by looking solely at the white balls (100 - 75=25 years) or just at the green balls (25 years). This isbecause we knew how many balls there were at zerotime. In a real rock we don't know how many radioactiveatoms there are to begin, so we must count both theparent and the daughter atoms because the total numberof white balls plus the total number of green balls addup to the original number of white balls before the

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decay process started. Rock dating is basically thatsimple. The machine used to measure the atoms is calleda mass spectrometer, and it allows one to count therelative number of each type of atom in a rock. Thepeople who make these measurements are called geo-chronologists.

Now we can think of three problems that mayinterfere with the accuracy of this process:

1 Radioactive decay constants change with time.2. Someone steals balls from the box or puts extra

balls into the box while we're away.3. There are extra green balls in the box before we start.

Radioactive Decay Constants ChangeAs we have seen, decay constants are a natural

function of the nuclear glue that holds the universetogether. You can't change them at random withoutdestroying everything around us What would be theresult of weakening the nuclear force enough to com-press the radiometric ages into a short time scale? First,many atoms that are stable now would decay intodifferent atoms. All life, which is dependent on complexmolecules such as DNA, enzymes, and proteins, wouldcease as the delicate binding and shape of these mol-ecules became totally disrupted by atoms turning intodifferent atoms.

Second, increased radiation from decay would belethal to life. Third, the amount of energy given offduring decay would probably be enough to totally meltthe surface of the earth. Radioactive decay even at itspresent slow rate is a major reason that the core of theearth is presently molten. Lastly, if this had happened inthe recent past, we would still find naturally occurringsimple radioactive elements with short half-lives (lessthan ten thousand years) not related to the decay of thelonger-lived isotopes, but this is not observed in nature.Changing the nuclear force by enough to make the datesfit a six- thousand-year chronology would be equivalentto making gravity a million times weaker in the past. Inshort, any change of this magnitude in nuclear forces isbound to leave behind evidence that we could see today.

Extra Balls Added to the BoxIn some rocks, atoms can be added or subtracted

by natural processes such as water percolating throughpore spaces. Geochronologists avoid this problem bychoosing minerals that are known to resist these pro-

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cesses and keep the parent and daughter populationlocked in. In addition, certain laboratory procedures canhelp identify whether loss has indeed happened.

Extra Green Balls Before e StartThe most interesting problem occurs when there

are already daughter elements present when the clockbegins to tick. This happens if the daughter element iscommonly available from nonradioactive sources.Luckily nature comes to our rescue here. It turns outthat because of the neutron, several different forms ofeach element exist. They differ only in their mass. Forinstance, there are four types of sulfur and three typesof silicon. These are called isotopes. In nonradioactiverocks, the ratio of these isotopes is the same everywhereon earth. By measuring these isotopes, we can formulateratios that represent the amount of contaminatingisotope at zero time. The calculated amount of contami-nating isotope can now be subtracted from the total inthe rock we are attempting to age.

The idea is much easier to understand in terms ofgolf balls. Let 's consider a box of one hundred whiteballs, with six green balls and two red balls alreadypresent. If we didn't account for the green balls, wewould estimate that the box was already six years oldbefore the clock even started. But if we know that innonradioactive rocks there are three green balls forevery red ball, we know that when we find the two redballs we have to subtract the six green balls before wecalculate any age. For instance, suppose we came backsome years later and found thirty-one green balls andtwo red balls. We subtract three green balls for each redball we find. Thus we have 31 - 6 =25 green balls due toradioactive decay, and we know the box is twenty-fiveyears old.

But what about the scientists who do the dating?Aren t they atheists who will hide any six-thou sand-yeardates and only publish the ones that are hundreds ofmillions of years old? Surprisingly, most scientistswhom I have met over the years have a belief in Godand are not out to prove that he doesn't exist. Physicalscientists are quite honest and forthright in their publi-cations for two very good reasons. First, the purpose ofpublishing is to let everyone know what you've discov-ered by your research. These results are almost alwayschecked by someone else sooner or later. If you lie orcheat, you will be caught and your career ruined. Second,as one geochronologist (who is an avowed atheist) oncetold me, I would love to prove the earth is six thousand

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Plot of Radiometric Ages vs Stratigraphic Sequence200 250 300 350 400

AhlNo, Trern iaLad sI:Zl .- AnScy0Cl( D TatZ pK8Z-Ufj Kun mS Art( D SakAI:lSte lrWas bNi frn fVis ,Tou Mp sozoic Pp rmian DevonianFam 200 250 300 350 400

Age Before Present (Ivlillion Years)years old if I could." What he meant was this: e wouldbe world famous and be remembered as the man who madea really significant discovery in earth science--the equiva-lent to finding a cure for all heart attacks in medicine.

So it is basically simple to get a rock to tell youhow old it is. Even potential problems that mightinterfere with this radioactive clock can be solved, andthe method is constantly being improved and refined.Many rocks can also be dated by two or more separateand independent methods. This gives us confidence thatthe ages we get from rocks are reliable, and, as youalready know, many of them are extremely ancient.They must be saying something important about theage of the earth.

Significance of Radiometric Datesto the History of Life

From a Christian point of view, the most startlingaspect of radiometric dating is the relationship betweenages and fossils in rocks. The different layers in rocksimply a sequence--the bottom rock being laid downbefore the younger rock, which is on top of it. But wealso observe a sequence of "critters" in these rocks.Certain critters are only found in young rocks andothers only in old rocks.

When the rocks on earth are classified into groupson the basis of distinctive critters they contain, we calleach of these units a "stage." Stages are defined strictlyby fossils and relative stratigraphy, and stage bound-

aries are usually marked by a arstinctive change incritter morphology or population. They represent asequence of younger to older rocks, but without furtherinformation we don't know whether this sequencerepresents one year or a billion. It is possible, however,to radiometrically date rocks that are associated witheach stage. As expected, we find that stages at the top ofa series are younger than stages at the bottom. But whatis really surprising is that the dates spread over hun-dreds of millions of years Even more amazing is theconsistency of the dates. Rocks containing a certain typeof critter only give a small range of ages for that critter.

Each stage, then, appears to be associated withrocks of a certain age range. This is really astoundingbecause stages are defined by fossils in rocks and strati-graphic relationships while ages are totally independent.Radiometric ages, as we have seen, are dependent onnuclear processes, not geology or critters. Yet, clearly,certain critters and certain ages are always correlated.The simplest explanation of this link is that the stagesreally do represent long intervals of time and that therocks involved could not have been deposited over ashort period of time. Any model we propose to describeearly earth history will have to satisfactorily explainresults such as these.

Richard Bottomley graduated from Atlantic Union Collegewith a degree in religion. After obtaining a doctorate inphysics he worked for Shell Oil in their exploration andresearch divisions. He teaches at the college level.bottomley@cnnet.comCREATION 47