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Sand dunes of the Sahara: How should we relate Scripture to earth science questions ?

A Christian scientist, while accepting the testimony of Scripture about God’s past intervention in Earth’s history, can still keep an open mind toward aspects of the geologic record that are unusual and different.

The Sahara is an immense region of northern Africa characterized by a hyper-arid climate. Apart from its iconic, historical, and ecological significance, the Sahara is also an object of great interest for Earth-science studies. Hidden among its grains of sand lies a wealth of information on geologic processes, landscape transformation, and environmental change. In addition, this vast desert environment could represent a modern analogue for the interpretation of parts of the rock record.

In this article, the Sahara Desert will be used to illustrate the type of questions and challenges inherent to the practice of Earth sciences, and suggest a general approach on how to relate knowledge about Earth history derived from biblical and scientific sources.

THE SAHARAN SAND1

Although the popular conception of the Sahara is probably one of a vast and continuous sea of sand, the reality is that sand covers only ~25 percent of the Sahara region. The remaining 75 percent mostly consists of barren terrain, from which fine-grained sediment has been blown away by the wind; and highlands with mountain massifs higher than 3,000 meters. About 30 distinct sand seas (named “ergs”) occur in the Sahara Desert, with an areal extent varying from several tens to a few hundred thousands of square kilometers. These ergs are usually located in topographically depressed areas downwind of mountainous regions. Published data on the thickness of sand cover in the sand fields are relatively sparse but suggest high variability, ranging from very thin, less-than-one-meter sand sheets to giant composite dunes up to 450 meters thick.2 Predominant wind directions in the Sahara region are controlled by patterns of atmospheric circulation and are generally consistent with an approximately N-S orientation in the eastern Sahara, bending clockwise to an ENE-WSW orientation in the western Sahara.

EARTH SCIENCE QUESTIONS AND SAHARAN SAND SEAS

Saharan sand seas provide an excellent illustration of the type of questions and challenges encountered in Earth-sciences research.

  • PROCESS QUESTIONS. A first set of questions has to do with process. How did these sand accumulations form? Where does the sand come from? What controls its distribution and the type of structures in which it is arranged?

    The first essential step in tackling process questions is a careful description of the object under investigation. Challenges at this stage arise from limitations intrinsic to the data-acquisition process and the complexity of the system under study. For example, sand deposits of the Sahara can be investigated at a variety of scales, from scanning electron microscope imaging of the surface of individual sand grains to satellite imaging of vast areas of the desert. At all scales, there is a risk of overlooking or misrepresenting important details. Once enough information has been collected, models can be developed to test a specific hypothesis. Models have their own limitations and assumptions, and their outcome often requires verification in the field.

    The consensus regarding the Sahara is that its sand comes mostly from the reworking of older alluvial sediments deposited by water, which were formed before the establishment of the current arid conditions. Therefore, the generation of sand granules and their accumulation by wind in large sand seas were distinct processes, happening in two separate phases.3 The size and distribution of the ergs are thought to be controlled by the location of uplands and topographic depressions, which are in turn a function of geological structures affecting the crust of the African continent.4 These conclusions are, however, still relatively generic and need significant refinement.

  • TIME QUESTIONS. The second set of questions typical of Earth-science research have to do with time. In the case of Saharan sand seas, one might want to know when they formed, how long it took, whether their formation was abrupt or gradual, and if it consisted of a series of distinct events or one single major event.

    Time issues are usually tackled using two main approaches, known as relative and absolute dating. Relative dating tries to establish a sequence of events, placing them in relative order (i.e., which event came first, which came after) but without assigning them a specific age. Absolute dating aims at attributing a specific age to the identified events (i.e., this event happened x years before the present).

    An example of relative dating in the Sahara is based on the occurrence of large, parallel linear dunes, upon which are superimposed smaller dunes with a consistently different orientation.5 Because the smaller dunes are atop the larger ones, this suggests they formed subsequently under a different wind regime. However, scientists are interested in knowing when exactly each generation of dunes formed. To accomplish this absolute dating, they must rely on some type of dating technique, each of which comes with its own assumptions and methodological limitations. Optically stimulated luminescence performed on sand grains is probably the only technique that can be applied directly to Sahara sand dunes to obtain numerical ages.6 More commonly, minimum and maximum age constraints can be obtained by applying radiometric dating to suitable material not found in the sands themselves but in other units in contact with them.

    The current consensus on some time questions relating to Sahara sand seas is as follows:

    1. The present Saharan configuration of a dry desert with vast sand seas appears to have been established relatively recently (in the order of few millennia ago), having being preceded by a time when the Sahara was a more verdant region.7 Evidence for this “green Sahara” phase includes remnants of extensive river networks and coast-lines of large lakes now buried under a sand cover but visible from satellite imaging and confirmed by field observations.8 Some studies indicate that this landscape transition might have been quite abrupt, with a duration in the order of tens to hundreds of years9;
    2. There might have been a series of fluctuations between humid and dry periods that affected the Sahara region. However, most scientists agree that the bulk of the sand ergs formed at the peak of the last glaciation and during the following deglaciation10; and
    3. It is difficult to precisely establish when the desertification trend in the Sahara region began. However, its onset is often considered coeval with the initiation of the Northern Hemisphere ice age11 developed over the most recent part of geological history.
  • ROCK RECORD QUESTIONS. A final goal in geology is the search for regularities that can help interpret general patterns in rock formations. The study of modern environments can be helpful in this search, assuming that physical processes acted in a similar way in the past. This approach, using the present to interpret the past, is called actualism. The Sahara Desert, for example, could represent a modern analogue useful for the interpretation of thick and widespread sandstone formations commonly considered as ancient examples of windblown sand seas. There are indeed many lessons applicable to rock formations that could be learned from the Sahara,12 but there seem to be enough significant differences to caution against a strict application of actualism.13

SCRIPTURE AND EARTH SCIENCES: CHALLENGES AND OPPORTUNITIES

Christian scholars are interested in understanding the relationship between the knowledge they derive from Scripture and the study of nature. While asking Earth-science questions, for example, Christian geologists ponder the role biblical information should play in their quest for answers. This interaction presents both benefits and challenges.

When evaluating process-related questions, for example, there is a fundamental difference between the biblical worldview, where God the Creator is active in history, and naturalistic explanations of origins that by definition exclude any type of divine activity. Being open to the notion of God’s involvement in nature implies that God may have acted in the past causing effects different from what we see today. Some passages of the Bible make explicit mention of this type of divine action (e.g., 2 Peter 3:3‒6). However, the genesis of many aspects of the geologic record, including sand dunes of the Sahara, is not directly addressed in Scripture. The Bible does not preclude the possibility that many of these geological objects are the result of the regular laws and processes through which God sustains the universe.

Time-related questions pose a different type of challenge. An area of current tension between the biblical and naturalistic models of Earth history has to do with absolute ages obtained through radiometric dating, which are in conflict with the short chronology of life on Earth based on biblical genealogies.14 In the case of the Sahara sand seas, the conflict is not as strident, given that conventional ages for these sand accumulations range in the thousands rather than hundreds of thousands of years. However, progressive aridification of the Sahara region is indeed commonly presented as a process that developed over a longer timescale (a few million years).

If challenges remain in the area of absolute dating, the Bible does provide a nice canvas that could act as a background for the relative sequence of more-detailed events seen in the geologic record. Creation, the Fall, and the Flood are a succession of mileposts provided in Scripture that help us organize different phases of Earth history. In the case of the Sahara sand seas, it is likely that their formation took place in the post-Flood era, because of their position in the very top part of the geologic column and their inferred relationship to the last ice age.

Finally, a Christian scientist accepting the testimony of Scripture about God’s past intervention in Earth history should keep an open mind toward aspects of the geologic record that are unusual and different.15 Modern processes and environments can still be considered valuable to define a baseline for comparison, but an overconfident application of actualistic principles should be avoided.

SCRIPTURE AND EARTH SCIENCES: A VALUABLE INTERACTION

When considering the wealth of information and detail that can be extracted from the study of the rock record, Christian scientists cannot but read it as a divine invitation to explore and study the complexity of a world that was created from the beginning by a God who gives with abundance.

We venture into this journey making use of the capacity for reasoning with which God endowed humans, but maintaining as foundational the historical canvas provided by biblical revelation. We acknowledge that Scripture does not address many details of Earth history and of the workings of the physical world. Nevertheless, we believe that one of the intentions of biblical authors was to provide factual and accurate information about the origin and history of humans and our world. The Bible does not specify when and how the Sahara sand seas formed, but it does tell of a recent six-day creation and a subsequent universal flood.

In the Christian arena, it is possible to find differing views on what significance and how much weight to place on specific aspects of the biblical text. This implies that when we read Scripture, we have a choice to make on what value we will assign to the Word of God. Does it provide accurate historical information; are the events described real; can we trust the details of the account? I have found that when we respond in the affirmative, Scripture powerfully clarifies questions about our existence, the character of God, and His interaction with humans throughout history.

In the Bible, we can discover not only a theological foundation, but also a framework for organizing observations such as the evidence for design, complexity, and vastness of the physical world, our ability to reason and comprehend how this world works, and the complex archive of past history locked in the rock record. When working within this framework with wisdom and humility, it is possible to let science and Scripture respectfully coexist in our quest for knowledge and meaning, even when questions still remain. There is much we can learn from the study of nature, as exemplified by the sand dunes of the Sahara. Let us choose to nest this learning within the context of a vibrant relationship with God.

“How precious to me are your thoughts, God!

How vast is the sum of them!

Were I to count them, they would

outnumber the grains of sand—

when I awake, I am still with you.”

―Psalm 139:17, 18, NIV.16

Ronny Nalin (Ph.D., University of Padua, Padua, Italy) is an Associate Scientist at Geoscience Research Institute, Loma Linda, California, U.S.A. He is also an Adjunct Faculty member in the Earth and Biological Sciences Department of Loma Linda University, Loma Linda, California, U.S.A.

Recommended Citation

Ronny Nalin, "Sand dunes of the Sahara: How should we relate Scripture to earth science questions ?," Dialogue 30:2 (2018): 11-14

NOTES AND REFERENCES

  1. Mostly based on Arthur S. Goudie, Great Warm Deserts of the World: Landscapes and Evolution (New York: Oxford University Press, 2002).
  2. I. G. Wilson, “Ergs,” Sedimentary Geology 10:2 (1973): 88-91, 93, 103, 104.
  3. Ibid., 84, 85; F. El-Baz, “Sand Accumulation and Groundwater in the Eastern Sahara,” Episodes 21:3 (September 1998): 147-151; Gary Kocurek, “Limits on Extreme Eolian Systems: Sahara of Mauritania and Jurassic Navajo Sandstone Examples.” In Extreme Depositional Environments: Mega End Members in Geologic Time, Marjorie A. Chan and Allen W. Archer, eds. (Boulder: Geological Society of America Special Paper 370, 2003), 43‒52.
  4. Wilson, “Ergs,” Sedimentary Geology, 81‒84; M. Williams, “Geology.” In Key Environments: Sahara Desert, J. L. Cloudsley-Thompson, ed. (Oxford, U.K.: Pergamon Press, 1984), 31‒39; Goudie, Great Warm Deserts of the World, 105, 106.
  5. Nicholas Lancaster et al., “Late Pleistocene and Holocene Dune Activity and Wind Regimes in the Western Sahara Desert of Mauritania,” Geology 30:11 (November 2002): 991‒994.
  6. Juan Pedro Rodríguez-López et al., “Archean to Recent Aeolian Sand Systems and Their Sedimentary Record: Current Understandings and Future Prospects,” Sedimentology 61:6 (April 2014): 1,518.
  7. Anne-Marie Lézine et al., “Sahara and Sahel Vulnerability to Climate Changes, Lessons From Holocene Hydrological Data,” Quaternary Science Reviews 30 (2011): 3,001‒3,012.
  8. Marc J. Leblanc et al., “Evidence for Megalake Chad, North-Central Africa, During the Late Quaternary From Satellite Data,” Palaeogeography, Palaeoclimatology, Palaeoecology 230 (2006): 230‒242.
  9. Peter deMenocal et al., “Abrupt Onset and Termination of the African Humid Period: Rapid Climate Responses to Gradual Insolation Forcing,” Quaternary Science Reviews 19:1‒5 (2000): 347‒361.
  10. C. Swezey, “Eolian Sediment Responses to Late Quaternary Climate Changes: Temporal and Spatial Patterns in the Sahara,” Paleogeography, Palaeoclimatology, Palaeoecology 167:1‒2 (2001): 119‒155; Lancaster et al., “Late Pleistocene and Holocene Dune Activity,” 991‒994.
  11. Christopher Swezey, “Cenozoic Stratigraphy of the Sahara, Northern Africa,” Journal of African Earth Sciences 53 (January 2009): 89‒121.
  12. Rodríguez-López et al., “Archean to Recent Aeolian Sand Systems,” 1,512‒1,522.
  13. Kocurek, “Limits on Extreme Eolian Systems,” 51; Rodríguez- López et al., “Archean to Recent Aeolian Sand Systems,” 1,512‒1,518.
  14. For a brief assessment of radiometric dating and its implications for a creationist perspective, see the Geoscience Research Institute (GRI) blog post “Radiometric Dating” (July 22, 2013) by Ben Clausen (July 22, 2013), available at https://grisda.word press.com/2013/07/29/radiometric-dating/.
  15. For an example of this approach, see the GRI blog post “Questions: Their Role in Discovery” (August 29, 2016) by Leonard Brand, available at https://grisda.wordpress.com/2016/08/29/ questions-their-role-in-discovery/.
  16. Quoted from the New International Version of the Bible.