Reports of the National Center for Science Education

Equal Time for the Origin of Granite


Creationists continue to push for equal time in science classrooms to teach that the Genesis stories in the Bible are valid scientific interpretations of earth history. Equal time for creationists' interpretations is not likely to occur in secular universities and schools, but if the creationists are serious about equal time, then they should be open to granting equal time in their private Christian schools for presentations of both sides of a scientific issue — a literalist biblical view and the modern science view. The origin, age, and other characteristic features of granite are such issues deserving equal time.

The Bible says that the dry land was created on Day 3 of the Genesis Week (Genesis 1:9-10), and presumably this is the time during which granite in continental masses was formed. However, Gentry (1988, p 129-3, 184-5) says that granite was formed both on Day 1 and Day 3 and that granite from both days can be mixed. He also claims that after Day 3, granite magmas must crystallize as rhyolite (the fine-grained volcanic equivalent of granite), rather than coarse-grained granite, and that granites penetrating the Flood deposits result from upheavals of solids but not magma.

Austin (1994) states that the majority of conservative Christian scholars, including Henry Morris, believe that the earliest rocks formed on Day 1. He interprets these to include the Vishnu schists of the Grand Canyon into which the Proterozoic Zoroaster granites were intruded on Day 3, when land and sea were separated. If I were given equal time in a science classroom at a private, fundamentalist, Christian college or secondary school which advocated young-earth creationist views, I would provide the following material and information regarding the formation of granite. This would allow students to compare a modern scientific interpretation of granite with the corresponding creationist biblical interpretation of granite being formed primarily in the Genesis Week.

Modern science's interpretation of granite

Origin. Geologists recognize several possible origins for rocks we classiify as granite(s) which depend upon the processes that operate on the rock systems. However, geologists agree that all granites form below the earth's surface. Some granites form (1) by magmatic processes — a crystallization of magma (melted silicate rock) — with the final form dependent upon crystal settling and the order of crystallization of minerals, (2) by melting of sedimentary rocks whose chemical composition is the same as that in granite, (3) by partial melting of rocks in which the first minerals to melt have the composition of granite; and finally, (4) by chemical replacement processes (Hyndman 1985; Clarke 1992; Collins 1988; Hunt and others 1992). Discussion of these different origins could be expanded here, but it is sufficient to say that modern scientific studies show that granite is formed in many different ways, and these ways contrast with the creationists' model in which granite has a single origin, being created nearly instantly by "fiat" (for example, Gentry 1988).

Mineral and chemical composition. In a general sense "granitic rocks" range in composition from true granite that is rich in potassium and silica to other coarse-grained igneous rocks, such as granodiorite, quartz monzonite, diorite, tonalite, and even gabbro, which are progressively less rich in potassium and silica and richer in iron, calcium, and magnesium (Hyndman 1985). This range in composition is recognized by Gentry (1988), but his emphasis is on biotite-bearing granite that contains Polonium (Po) halos, and, therefore, the same emphasis will be used in this article. For a discussion of Po halos, see also Collins (1988), Hunt and others (1992), and Nevertheless, the reader can substitute the broader term "granitic rocks" that include the above compositional range in most places in this article where granite is mentioned without being in conflict with Gentry (1988).

True granite is not a pure substance but is a mixture of several different silicate minerals and oxides (Clarke 1992). In the true sense it commonly consists of about one-third quartz, one-third potassium feldspar, one-third plagioclase feldspar, minor amounts of iron- and magnesium-bearing biotite (black mica), and traces of various accessory minerals, including zircon (mentioned later). In addition to biotite, other varieties of true granite may contain small amounts of other iron- and magnesium-bearing silicates or muscovite mica, but biotite granite is the most common variety. In all true granites, however, quartz and feldspars are the dominant mineral species, making the rock white, light cream, or pink, but speckled with one or more of the dark iron-bearing minerals.

Liquid characteristics. In the field, granite can be seen to intrude into other rocks and in some places to exhibit flow banding, both of which are characteristic of moving liquids or plastic solids. Furthermore, in many places fragments of older rock along the walls of a granite body are broken off and enclosed in the granite as inclusions of large or small size, adding further evidence for the liquid origin of the granite body when it was first formed. Finally, if a granite body has a liquid origin, it should have the capability of mixing with other liquids, such as basalt magma, and this mixing is evident, for example, in Maine (Wiebe 1996) and in other parts of the world (cited in Wiebe 1996). Gentry (1988, p 185) also allows for mixing of magma but disregards the physical characteristics of magma, such as its heat capacity and cooling rates that are discussed in a later section.

Order of crystallization. Experimental work in which natural granites are melted in the laboratory shows that a granite in a liquid state would be a water-bearing silicate melt (magma) at temperatures as high or higher than 900°C (Huang and Wyllie 1981). When this silicate melt is cooled and crystallized to become granite, not all of its various minerals crystallize at the same time, but each forms in a specific range of temperatures and in a definite order. The iron-, magnesium-, and titanium-bearing silicates and oxides crystallize at relatively high temperatures whereas the feldspars form at lower temperatures, and quartz is the last to crystallize near 550-650°C, depending upon pressure and other components. This order of crystallization is consistent world-wide regardless of whether the granite is Precambrian in age or younger or whether the granite is attributed to be formed on Day 1 or Day 3.

Evidence for high temperatures of natural granites. Geologists find evidence for the high-temperature crystallization of a granite body by using what are called "geologic thermometers". For example, in an experiment, biotite mica and garnet are crystallized simultaneously from melts. The results show that iron and magnesium atoms are partitioned from the melt into these 2 minerals in different ratios and that these ratios will differ depending on temperature and pressure conditions (Ferry and Spear 1978). By measuring these ratios in biotite and garnet found together in natural granites and comparing them with ratios obtained at different temperatures and pressures in the experimental work, geologists find that the temperatures for the final crystallization of these two minerals in natural granites are commonly higher than 700°C — the presence of certain minerals or combinations of minerals provides a standard or scale for measuring temperature, that is, a sort of geological thermometer. Garnet is not common in granite, but "two-feldspar" and "magnetite-ilmenite" are 2 other common "geologic thermometers" used to measure temperatures in granites. These thermometers also have experimental support, and both mineral pairs give similar high temperature values for the crystallization of granite (Bohlen and Lindsley 1987; Hyndman 1985).

Further evidence of the high-temperature origin of granite is the contact metamorphic aureole that occurs in sedimentary rocks where they are intruded by granite magma. The minerals found in sediments are generally stable near 25°C and one atmosphere of pressure and result from weathering processes at the earth's surface. When these minerals are heated to temperatures approaching those of an adjacent hot granite magma, some (such as quartz) will remain as the same mineral but will recrystallize and increase in size while others will form new minerals that are stable at higher temperatures and pressures. For example, fine-grained fossil-bearing limestones that consist of calcite (calcium carbonate), which are intruded by granite magma, commonly recrystallize as coarse-grained calcite marbles; in this process the fossils are destroyed as the tiny calcite crystals in the fossils grow in size.

On the other hand, sedimentary shales, consisting mostly of aluminum-rich clay, are recrystallized to form other aluminum-rich minerals, some of which are stable at the highest temperatures closest to the granite contact; others are stable at intermediate temperatures at greater distances away; and still others are stable at lower temperatures at even farther distances from the contact (for example, Pitcher and Berger 1972; Holtta 1995). Such features of high-temperature contact-metamorphism of sedimentary wall rocks, called aureoles, are found world-wide around most granite bodies of large size and range from a few to a thousand meters wide or more. Their existence supports the concept that these granite bodies were intruded as a very hot magma. If Gentry (1988, p 185) wishes to have the metamorphic aureole be formed by hot fluids associated with solidified granite, then these hot fluids should also have caused the granite to produce lower-temperature minerals like that found in the aureole, and that is not the case.

Age of Granites. The field evidence supports the concept that not all granites are formed at the same time as other rocks with which they may be adjacent and that some granite bodies are younger in age than other granites. The fact that granite bodies intrude other rocks (by filling in cracks, for example, to form dikes) indicates that the other rocks are older in age than the granite. The intruded rocks have to be there first before the granite can cut through them. In some places granite masses of one type cut across other granite bodies, which also shows that some granites are younger than others. The fact that granites also have several possible different origins, as described earlier, also implies different ages for granite.

For example, if some granites are derived by melting of sediments, erosion of a continental land mass must occur first to produce the sediments. Then, the sediments must be deeply buried, and a strong heat source must be found before the granite can be formed from them. Although Gentry (1988, p 133, 184-5) allows for granite to be formed both on Day 1 and Day 3, the field evidence shows that the mixing of granites of 2 different ages is not by faulting or intrusion of solid rock into solid rock during earth upheavals but only by mixing of 2 "granitic" liquids or by penetration of a "granitic" liquid into a solid. As indicated in the previous sections, this liquid must be in the form of hot magma.

Furthermore, additional age and hot-liquid-origin relationships can be seen for granites that are supposedly formed in Day 3 but cut the Noachian Flood deposits and, therefore, are younger than Day 3. For example, Precambrian granite bodies in the bottom of the Grand Canyon in Colorado have an erosion surface on which the horizontal, Paleozoic, fossil-bearing sediments are deposited, with the Cambrian Tapeats sandstone at the bottom and the Permian Kaibab limestone at the top (Elders 1998). The eroded surface indicates that these granites are older than these sediments, the so-called "Noachian Flood deposits." On the other hand, the Donegal granites in northwest Ireland intrude and enclose inclusions of sedimentary rocks of Cambrian age, illustrating that the granites are younger than the Cambrian deposits, whose contacts with the granites have a high-temperature metamorphic aureole (Pitcher and Berger 1972). This field evidence shows that the sedimentary rocks are not faulted into the solid granites but enclosed in the granites when the granites were hot magma.

The same kinds of metamorphic contact-relationships are found in the granites that intrude fossil-bearing sediments in Maine, Connecticut, and Rhode Island (Harrison and others 1983). The Narragansett Pier granite in Rhode Island surrounds inclusions of Pennsylvanian metamorphosed sediments containing flora fossils, Annularia stellata (Brown and others1978). The flora fossils are now totally carbonized as graphite, indicating the high temperature of the granite body that metamorphosed the sedimentary inclusions. The fact that the granite contains inclusions of these fossil-bearing sediments makes the granite younger than these supposed "Flood" sediments.

The Sierra Nevada granite intrusions in California also have intruded and metamorphosed supposed "Flood sediments" in roof pendants containing Ordovician graptolite fossils (Frazier and others 1986) and Pennsylvanian brachiopod fossils (Rinehart and Ross 1964; Rinehart and others 1959). In other places, the Sierran granites have intruded and metamorphosed "Flood sediments" containing Triassic ammonites (coiled cephalopods; Smith 1927). A granite in the Mojave desert in California near Cadiz intrudes Cambrian limestone containing stromatolite fossils. At the contact, this limestone is converted to marble with high-temperature metamorphic minerals, but remnants of the stromatolites can still be found (Richard Squires, oral communication 1998). Thus, it is very clear from the above examples that some granite masses are the same age as or even younger than the "Noachian Flood deposits".

Absolute ages of granite bodies, rather than relative ages, can be obtained by using various radioactive isotopes; that is, uranium-lead (U/Pb), potassium-argon (K/Ar), and rubidium-strontium (Rb/Sr) age-dating techniques (Dalrymple 1991). For example, trace amounts of uranium and lead are dissolved in the granite melts. Uranium and lead ions have entirely different chemical characteristics, and they normally crystallize in entirely different minerals. Because the uranium ion is about the same size as the zirconium ion, uranium will substitute for zirconium and crystallize in zircon, but the lead ion goes elsewhere, commonly in potassium feldspar, as the granite magma crystallizes. But the isotope of uranium (238U) is radioactive and eventually decays to form lead (206Pb). When the granite first crystallizes and the radioactive uranium enters the zircon crystal (devoid of 206Pb), the clock is set and "ticking," and the uranium is constantly breaking down, eventually to produce new lead (206Pb) atoms trapped in the zircon crystals.

Because this U/Pb decay-scheme is a constant, the ratio of uranium to lead in zircon populations in granite can be used to determine the age of a granite. World-wide the absolute ages of various granite bodies are consistent with the relative ages described above (Dalrymple 1991). For example, granites in the bottom of the Grand Canyon give Precambrian ages of 1740 — 1710 and 1700 — 1660 billion years, younger than 2 different units of Vishnu schist with ages of 1750 and 1742 billion-years-old (Ilg and others 1996), which the granites intrude, and older than the overlying "Noachian Flood deposits" of about 540 million years for the Cambrian Tapeats sandstone at the bottom to the 225-million-year-old Permian Kaibab limestone at the top. The Narragansett Pier granite that contains 300-million-year-old Pennsylvanian flora fossils (Brown and others 1978) indicates that this granite is younger than the sediments, and this is confirmed by the U/Pb age-date from zircon populations of 273 million years (Zartman and Hermes 1987). And granites in the Sierra Nevada give Jurassic and Cretaceous ages of 66 to 208 million years old that are younger than the rocks (about 230 million years old) containing upper Triassic ammonites, which these granites intrude.

Occasionally, some granites give apparently anomalous isotopic "ages," and some Cenozoic basalts give an age greater than the 4.5-billion-year-age of the earth (Hedge and Noble 1971). These facts are commonly harped on by creationists who are critical of isotopic age-dating methods (for example, Austin 1994). But in these places, logical explanations suggest reasons why the dates are unusual. Close examination generally shows that, where unusual age "dates" are obtained from granite samples, other processes have affected the granite to cause the anomalous dates. For example, the granite may have been deformed and fractured so that fluids have entered and altered the isotopic ratios. Where granites have been dated by the Rb/Sr age-dating method, anomalous measurements are not unusual because of the susceptibility of rubidium and strontium to be added or subtracted by the movement of introduced fluids through fractures and deformed crystals. (Collins 1988; Hunt and others 1992).

The K/Ar age-dating method can also give values that differ from U/Pb age measurements because heat generated from the intrusion of another nearby igneous mass has allowed some of the argon gas to leak. In each of these places, the unusual or unexpected age dates are not a failure of the dating method, but an indication that other events have occurred in the geologic history of these rocks. See also a discussion and explanation of the anomalous age dates of basalts in the Grand Canyon and the reporting of more recent age-dating that gives results consistent with the geologic terrane (Elders 1998, p 13-4).

Geologists realize that apparently inconsistent "dates" can occur and seek to find out why they occur, knowing that the isotopic age-dating technique, itself, is not at fault. Should we re-evaluate the usefulness of radiometric dating then? For example, the following analogy can be used. Water-proof wrist watches that can be worn by scuba divers generally keep good time, but occasionally these watches fail and give faulty time. When that happens, an examination of the watch shows that it has been damaged so that a crack in the holding case has occurred, and water has leaked into the clock mechanism. The faulty time is not because the watch is improperly designed but because water has corroded the gears in the clock. On that basis, a person does not throw out all clocks or watches or cease to buy them, but rejecting all radiometric dating is seriously suggested by creationists.

Likewise, when isotopic age-dating of granites or other igneous rocks produces unexpected or illogical age dates, one does not throw out the whole system of isotopic age-dating. In some disturbed and deformed rocks, the "clock timing mechanism" has been "upset" by "corrosion" or some other factor, and the faulty date is a clue to the geologist to look for the cause. The primary reason for accepting the isotopic age-dating methods is because, in many places, world-wide, where several different kinds of isotopic age-dating methods have been applied to the same rock, all age determinations were found to be about the same (Dalrymple 1991). This equality of measured dates gives confidence that the isotopic age-dating methods are valid scientific procedures. The vastly different half-lives of the radioactive isotopes in each age-dating method and the completely different chemical characteristics of the isotopes make the arrival at the same age dates not a purely coincidental. The age dates must be controlled by physical laws that are very dependable.

Heat capacity of granite. Measurements can be made to determine the heat capacity of a block of granite at a given temperature and also to determine the rate of heat conduction as such a block cools from a higher to a lower temperature. Such laboratory measurements are commonly done by using a calorimeter, and they show that blocks of granite are very poor conductors of heat. If a body of granite magma had a surface area of 30 to 50 square kilometers and a depth of 20 to 35 kilometers (a typical size of a small granite body), the total amount of heat (calories) stored in such a granite mass at a temperature of 900°C is enormous. But, significantly, the heat conduction experiments show that the rate at which this heat is lost by conduction must be very slow. Calculations show that such a volume of granite magma would take several millions of years to cool down from 900°C to near 550-650°C, where it would totally crystallize, and then finally to cool to the 25°C temperature found at the earth's surface.

Pitcher (1993) estimates that a granite body, depending upon its size and depth of burial, cools no faster than 25 to 250°C per million years. This slow cooling is indicated by deeply buried granite magma still giving off heat in the Coso Range of east-central California, containing rhyolite flows (volcanic equivalent of granite); the residual heat is being utilized for steam generation and electrical energy (Bacon and others 1980). An even better example is the Kakkonda geothermal field in a Quaternary granite (younger than 1.1 million years old) that occurs in Japan. Drilling in this granite reveals temperatures of 500(C (Ikeuchi and others 1996). Finally, because many batholiths consist of multiple intrusions of different granitic bodies and because many of the earlier-intruded bodies have completely solidified before subsequent intrusions have occurred, their heat capacities and slow cooling rates imply millions of years for such large volumes of igneous rocks to be formed.

Although the heat capacity of granite is emphasized in this section, similar problems for young-earth creationists are created by the heat capacity of basalt and the cooling rates of large masses of basalt in the oceanic basins. If this basalt were all deposited during the Genesis Week and in the supposed subsequent few thousand years until the present, it should not yet be solidified (see Strahler 1987, p 213-4).

Literal biblical interpretation of granite

When creationists make a literal interpretation of the Genesis accounts for the origin of granite (for example, Gentry 1988), they seek new data to support their views, and ignore or explain away information that contradicts their views. The literalists accept the Genesis accounts as being accurate, only requiring "research" to support their interpretation. Again, creationists are selective in choosing only the scientific data that fit their model of creation and discarding everything else. This procedure is not characteristic of the scientific method.

The creationists' interpretation of granite, when applied to Genesis 1:9-10, is that all granite masses were formed on Day 3 and perhaps Day 1 of the Genesis Week (Gentry 1988, p 133, 184-5). Although Gentry suggests the possibility that the granite formed from melts, his suggested rate of crystallization is many, many times faster than natural laws would allow. Gentry (1988, p 130-1) says that after Day 3 granite magma would form rhyolites and not granite and that during the Flood, some of the granites formed in Day 1 and Day 3 were intruded into the Flood deposits by upheavals as solids. These interpretations are not supported by field evidence, microscopic studies, and experimental work, and they are clearly not accurate because some granite bodies must have been produced from magmas at different times later than Day 3 (either during or after the supposed Noachian Flood as indicated by the metamorphosed fossil-bearing enclaves).

Moreover, if Precambrian granite were produced nearly instantaneously during Day 1 or Day 3, all physical laws would have to be abandoned, and this granite must have been created by a miracle. Even if creationists were to acknowledge that some granite was produced during and after the Noachian Flood, and they cannot deny the evidence, then all physical laws for cooling rates and crystallization would also have to be ignored. Such granites could not be emplaced and solidified in less than one year and not even in 6000 to 10 000 years, if the physical laws governing crystallization and cooling rates are obeyed. Furthermore, if all the heat from the world-wide granite magmas that penetrated the supposed Flood sediments were released suddenly in one year's time to the Noachian Flood waters in order to crystallize the granite masses abruptly, the waters would be heated so hot that the oceans would be boiling and no marine life would survive. Isn't it odd that the chronicles of Noah never commented on this phenomenon! One can teach a rapid formation of granite, but it is not teaching science. The literalist interpretation has to be saying that all granite bodies are formed by miracles.


Equal time, when used to discuss the origin of granite, clearly shows that the creationists' literal interpretation of the Genesis stories in the Bible has no validity for presentation in the science classrooms at secular schools because it is not science. It may have a place in some Christian schools where science is taught as miracles.
By Lorence G Collins
This version might differ slightly from the print publication.