The Faint Sun Paradox

The Faint Sun Paradox

Debates over global warming—how to measure it, the causes and effects, what to do about it and when—have raged for decades, with no resolution yet in view. Huge media coverage and multiplied millions of research dollars have focused on the possible impact of a fraction-of-a-degree average temperature increase worldwide over the span of a century or so.

Meanwhile, in a quiet corner, scientists express amazement at discoveries of the intricate pattern of events supporting survival through a solar warming so huge as to render the current (potentially devastating) crisis miniscule. In addition to stirring concern for the environment, global warming studies help highlight one of the greatest unsolved puzzles of nature since life first entered Earth’s formless void.

Solar researchers have found that 3.86 billion years ago,1 in the era when life appeared on Earth, the Sun was 30% less luminous (fainter, or less radiant) than it is today.2 Knowing that a drop of only 1-2% in the Sun’s brightness (under current atmospheric conditions) would transform Earth into a giant snowball—and that a 1-2% brightening would boil away the oceans and cook all life—scientists had to ask: How did life get started, survive, and ultimately thrive on Earth through millennia of continuous increase in solar radiation levels? As they put together the giant puzzle pieces of research on the faint Sun paradox, a wondrous picture begins to emerge.

The Puzzle Box Spills Open

The birth of the Sun began with the gravitational collapse of a gas cloud. During its collapse phase, the Sun at times accreted gas and dust and at other times lost gas and dust to outer space. During this infancy period, lasting about 50 million years, certain nuclear reactions turned on and off, rendering the Sun’s intensity of light and heat radiation—its luminosity—highly unstable.3 During the next five hundred million years, solar ionizing radiation, in particular x-rays, persisted at a level fifty times higher than today’s level.4 The extreme instability of the Sun’s luminosity and the high intensity of its ionizing radiation contributed to Earth’s inhospitality to life before 3.9 billion years ago.

Soon after the Sun’s first 50 million years, its core temperature rose to nearly 17 billion degrees Centigrade (31 billion degrees Fahrenheit), igniting the fusion of hydrogen into helium. For the first time in the Sun’s history, energy released from its interior nuclear reactions fully compensated for the energy lost (via radiation) at its visible surface, or “photosphere.” At this time, the Sun entered its long, stable, and gradually more radiant burning cycle.

The ignition of nuclear fusion gradually increased the ratio of helium to hydrogen in the solar core. Since helium is denser than hydrogen, and since higher core density means more efficient nuclear fusion, this ignition triggered a cycle: higher core density, thus higher core temperature, thus more efficient fusion, thus higher core density, and so on.

This fusion cycle translated into a brighter and brighter Sun. This gradual brightening will continue until nuclear fusion has converted all the hydrogen in the Sun’s core (the innermost 10% of the Sun’s mass) into helium.5 How long does this conversion process take? Astronomers calculate that for a star the mass of the Sun, the whole process takes 9 billion years. Based on the Sun’s current luminosity and other characteristics, astronomers say the Sun is almost exactly half way through its stable burning phase. They expect it to continue brightening for another 4.5 billion years.6

The Pieces Begin to Fit

Astronomers and geophysicists see abundant evidence that despite the Sun’s significantly lower luminosity at the time, 3.86 billion years ago Earth’s surface temperature was only marginally different from the current surface temperature. Both liquid water and life began to abound at that time.7 An elegantly simple and enormously complex explanation shows how such a phenomenon could be.

Though the Sun’s radiation was 30% fainter, Earth’s atmosphere compensated by trapping more heat. Just when it needed them, Earth happened to possess just-right quantities of “greenhouse” (heat-trapping) gases, such as carbon dioxide, water vapor, and methane. Therefore, though the Sun yielded less heat and light in the era when life first appeared, Earth’s atmospheric gases swaddled the planet in a sufficiently warm, protective blanket.

This phenomenon alone is enough to strike a person with awe, but the ongoing balancing act, whereby Earth maintained that just-right temperature for nearly 4 billion years, increases the sense of wonder. If at any time the quantity of greenhouse gases had dropped too far too fast or stayed too high for too long, no one would be here to make measurements and marvel at the precision.

Understanding the Fit

Two known mechanisms were involved in the delicate process of gradually removing greenhouse gases from Earth’s atmosphere as the ancient Sun brightened: (1) a continuous supply of exposed-to-the-atmosphere silicates (compounds containing silicon, oxygen, and metals that comprise more than 90% of Earth’s continental crust); and (2) a continuous burial of carbon-rich organic matter.

In the presence of liquid water, silicates gobble up (chemically react with) carbon dioxide from the atmosphere, forming carbonates and sand in the process. (See figure.) Bringing these silicates into contact with the atmosphere, where they can do their part in carbon dioxide reduction, requires a balanced cycle of crustal uplift and erosion. First, efficient plate tectonics must help create silicates, then push them above the ocean forming islands and continental land masses. Then, erosion must “plough” the crust so that more silicates are constantly brought into contact with the atmosphere.

Erosion itself is a complicated process. Multiple factors determine its efficiency, including (among others) Earth’s rotation rate, average rainfall, average temperature, average slope of the land masses, and the types and quantities of plant species on the land masses. If erosion proceeds too slowly, silicates cannot maintain an adequate pace of carbon dioxide removal. Too much erosion removes too much, too quickly.

Meanwhile, organisms, in particular photosynthetic plants, plus bacteria and methanogens (methane consuming bacteria), also work to take water, methane, and carbon dioxide from the atmosphere, chemically transforming them into fats, sugars, starches, proteins, and carbonates. If these compounds get buried before they can decay or be eaten by other organisms, they help in the task of reducing greenhouse gases. (As a bonus for humans, they also form a wealth of biodeposits such as limestone, marble, fossil fuels, and concentrated metal ores.) Major contributors to the burial process—in addition to wind and water erosion—are volcanic activity and plate tectonics.

In other words, fine-tuning removal of greenhouse gases to compensate for the increase in solar luminosity requires fine-tuning all the factors that govern silicate erosion, plus all the factors that govern the quantity, growth, diversity, decay, and burial of organisms.

A Completed Section

Until recent years, the one piece of the faint Sun puzzle most likely to be taken for granted was the adequate abundance of exposed silicates. The sole provider of this abundance was plate tectonic activity, which must not be overlooked.

Earth needs three things for plate tectonics to occur: 1) a stable, efficient dynamo (electromagnetic generator) at its core, 2) a powerful interior source of radioactive decay, and 3) an abundant supply of liquid surface water. The presence of any one of these would be “unexpected” by natural processes, but all three joined together boggles the mind. A closer look at each feature reveals more of the picture.

Earth’s dynamo, for example, works with enduring stability and efficiency because several independent factors fall within certain narrow ranges. These factors include (1) solar and lunar gravitational torques; (2) the frequency or period of the core’s gyrations (its “precession”); (3) the ratio of the inner core radius to the outer core radius; (4) the relative abundances of silicon, iron, and sulfur in the solid inner core; (5) the outer core’s magnetic Reynolds number (a measure of viscous flow behavior in the magnetic medium); (6) the ratio of inner core magnetic diffusivity (a measure of how well a magnetic field diffuses throughout a conducting medium) to outer core magnetic diffusivity; and (7) the viscosity of the material at the boundaries between the solid inner core and the liquid outer core, also between the liquid outer core and the mantle.8

As for the presence of the necessary radioactive elements, two very unlikely events brought it about. First, the gas cloud that condensed into the Sun and its planets formed adjacent to both the fresh remnant of a Type I supernova and the fresh remnant of a Type II supernova.9 Each contributed radioactive and life-essential heavy elements to the emergent solar system.

Then an amazing collision event brought about further enrichment. Between 4.5 and 4.4 billion years ago, a planet about the mass of Mars (one-ninth the mass of Earth) crashed into Earth. It hit at the optimal speed, angle, and location to transfer its radioactive and other heavy elements to Earth’s interior. The lighter material of both the collider and Earth formed a debris cloud around Earth that later condensed to become the Moon.10

This newly increased abundance of radioactive material contributed strategically to plate tectonic activity, which in turn contributed to the exposure of silicates, which in turn contributed to the steady, life-sustaining reduction of Earth’s greenhouse gases. The cycle began with the decay of radioactive elements in Earth’s interior. The decay served as a heat source, generating convective cells, like giant eddies, throughout the mantle. As the warm eddies reached all the way up through the region just under the crust, they began to impact the crust. Specific crustal regions became associated with specific mantle eddies.

In cases where sufficient liquid water was present at the boundaries between these crustal regions, the tectonic process called “subduction” began—the sliding of one crust piece (or plate) under another. Subduction was helped along as minerals in the subduction zone (the place where two underwater plates came together) became involved in the hydration process.11 Hydration led to the production of a talc layer that served as a lubricant for the tectonic plates. The friction-reducing lubricant facilitated the movement of one tectonic plate under another.

This same hydration process (the hydration of basalts) produced more and more minerals, or silicates, which are less dense than the nonhydrated basalts and have a lower melting point. The silicates tend to float above the denser basalts, thereby forming mountains. Because of their lower melting point, some of these silicates remain liquid as they rise closer and closer to the surface, thus fueling the formation of volcanoes.

The development of mountains and volcanoes eventually raised landmasses above the surface of the ocean. Through time, several of these landmasses grew to become continents.

Another Tricky Section

The hope of removing enough greenhouse gases from the atmosphere to keep up with the increasing luminosity of the Sun rested on yet another remarkable sequence of events. The build-up of continental landmasses through plate tectonics must have initially exceeded, and later kept up with, the reduction of continental landmasses through erosion. The difficulty Earth faced was that the energy released from radioactive decay declines over time, thus it contributed less and less toward maintenance of plate tectonic activity.

However, the collision that helped enrich Earth with radioactive elements also gave Earth a single gigantic moon. (Earth’s moon is more than one hundred times larger, in proportion to its planet, than Ganymede, Jupiter’s largest moon.) Earth’s moon acts as a tidal brake, with its gravitational tug gradually slowing Earth’s rotation rate. Strategically, this slower rotation rate results in a just-right decrease of erosion.

The convergence of so many intertwined, delicately balanced, and carefully timed factors has led many scientists to conclude that Earth is likely the only planet in the universe to possess long-lasting large oceans and continents.12 Earth must be considered an amazing rarity among planets, however abundant planets may be.

Life Provides a Crucial Piece

With more pieces in place, the faint Sun picture unfolds. As plate tectonic activity and rotation rate declined, new help was needed to maintain adequate levels of greenhouse-gas consumption. As if on cue, living creatures played their part. The essential species and the entire matrix of life-forms supporting their existence—in other words, entire ecosystems—existed at the right population levels in the right locations at the right times to assist in controlling the quantity of greenhouse gases, that in turn has kept Earth’s temperature in life’s safe range for nearly four billion years.

This regulation of Earth’s surface temperature in the context of a brightening Sun mandates a carefully timed progression—the introduction of life-forms and replacement of some kinds with new and different ones through time. For example, the most advanced plants on Earth, those that conduct fluids and nutrients through vascular bundles, are far more efficient than other plant species in accelerating erosion.13 So, as plate tectonics and erosion gradually decline, Earth needs more and more of these advanced plants to sustain adequate carbon dioxide removal from the atmosphere. This increase in advanced plants means a commensurate decrease in primitive plants to make room in the ecosystem.

Missing Pieces

Greenhouse gases still contribute to maintaining a safe temperature. In fact, Earth’s surface is currently warmer by 33° Centigrade (60° Fahrenheit) than it would be without those gases. However, the various forces that have worked so long to reduce those gases, as demanded by the brightening Sun, cannot keep pace forever.

The two major heat trappers today are water vapor and carbon dioxide, with water vapor playing the much bigger role. But to sustain life, Earth cannot afford to lose much of either gas. To reduce water vapor would be to reduce rainfall. This would expand deserts and decrease life-forms able to consume carbon dioxide.

But even if more carbon dioxide could be consumed, life would still be in trouble. Photosynthesis demands a certain minimum level of carbon dioxide in order to continue producing oxygen. Currently, carbon dioxide accounts for 375 parts per million in Earth’s atmosphere. When the atmospheric carbon dioxide level falls below about 225 parts per million, all photosynthetic life will die. Then, all animal life will die too.

Continued reduction of greenhouse gases can (possibly) extend the window of time for life on Earth by approximately 0.02 billion years. Without some reduction, large advanced animals will disappear first. Bacteria will be the last to go extinct.

Completing the Picture

The timing of humanity’s arrival—near the end of life’s long tenure on Earth—may appear tragic at first glance. But a longer look suggests it may be viewed as a gift. Scanning the horizon of civilization—farms, ranches, towns, cities, and all the transportation and communication arteries linking them—one sees a plethora of building materials derived from nearly 4 billion years of life and death: gems, sand, steel, asphalt, concrete, copper, limestone, marble, plastics, etc. Most of the energy that drives civilization comes from biodeposits—oil, coal, wood, kerogen, natural gas, and so forth. Many of the fertilizers that support agricultural production also come from biodeposits—phosphates, nitrates, and such.

Such bountiful provisions powerfully indicate a Provider who carefully planned and prepared the planet through the ages for human life. They speak of a purpose for the human race. The Bible reveals a purpose that involves, yet goes beyond, the current “heavens and Earth.”14

Everywhere that scientists look for answers to the faint Sun paradox, the pieces of supernatural design keep coming together. The more they study the paradox, the more evidence they discover for intentionally and intricately balanced complexities.15

Likewise, the faint Sun paradox merits further study, a deeper and wider search for pieces that complete the picture. The probing that will solve the puzzle not only enriches the investigators’ understanding of human nature, but also magnifies their respect and appreciation for the One who designed the picture in its entirety.


  1. S. J. Mojzsis et al., “Evidence for Life on Earth Before 3,800 Million Years Ago,” Nature 384 (1996): 53-59.
  2. Hugh Ross, The Creator and the Cosmos, 3d ed. (Colorado Springs, CO: NavPress, 2001), 180-81.
  3. Icko Iben, Jr., “Stellar Evolution. I. The Approach to the Main-Sequence,” Astrophysical Journal 141 (1965): 993-1018.
  4. Frederick M. Walter and Don C. Barry, “Pre- and Main-Sequence Evolution of Solar Activity,” in The Sun in Time, eds. C. P. Sonett, M. S. Giampapa, and M. S. Matthews (Tucson: University of Arizona Press, 1991), 633-57. (See Table IV, p. 653.); Masahiro Tsiyimoto et al., “X-Ray Properties of Young Stellar Objects in OMC-2 and OMC-3 from the CHANDRA Observatory,” Astrophysical Journal 566 (2002): 974-81.
  5. M. Schonberg and S. Chandrasekhar, “On the Evolution of the Main Sequence Stars,” Astrophysical Journal 96 (1942): 161-73.
  6. David S. P. Dearborn, “Standard Solar Models,” in The Sun in Time, eds. C. P. Sonett, M. S. Giampapa, and M. S. Matthews (Tucson: University of Arizona Press, 1991), 173.
  7. C. Sagan and G. Mullen, “Earth and Mars: Evolution of Atmospheres and Surface Temperatures,” Science 177 (1972): 52-56; H. D. Holland, The Chemical Evolution of the Atmosphere and Oceans (Princeton: Princeton Univ. Press, 1984); S. J. Mojzsis, et al., 53-59.
  8. Jihad Touma and Jack Wisdom, “Nonlinear Core-Mantle Coupling,” Astronomical Journal 122 (2001): 1030-50; Gerald Schubert and Keke Zhang, “Effects of an Electrically Conducting Inner Core on Planetary and Stellar Dynamos,” Astrophysical Journal 557 (2001): 930-42; M. H. Acuna et al., “Magnetic Field and Plasma Observations at Mars: Initial Results of the Mars Global Surveyor Mission,” Science 279 (1998): 1676-80; Peter Olson, “Probing Earth’s Dynamo,” Nature 389 (1997): 337; Weiji Kuang and Jeremy Bloxham, “An Earth-Like Numerical Dynamo Model,” Nature 389 (1997): 371-74; Xiaodong Song and Paul G. Richards, “Seismological Evidence for Differential Rotation of the Earth’s Inner Core,” Nature 382 (1997): 221-24; Wei-jia Su, Adam M. Dziewonski, and Raymond Jeanloz, “Planet Within a Planet: Rotation of the Inner Core of the Earth,” Science 274 (1996): 1883-87.
  9. Peter Hoppe et al., “Type II Supernova Matter in a Silicon Carbide Grain from the Murchison Meteorite,” Science 272 (1996): 1314-16; G. J. Wasserburg, R. Gallino, and M. Busso, “A Test of the Supernova Trigger Hypothesis with 60Fe and 26Al,” Astrophysical Journal Letters 500 (1998): L189-L193; S. Sahijpal et al., “A Stellar Origin for the Short-Lived Nuclides in the Early Solar System,” Nature 391 (1998): 559-61.
  10. Sigeru Ida, Robin M. Canup, and Glen R. Stewart, “Lunar Accretion from an Impact-Generated Disk,” Nature 389 (1997), 353-57.
  11. Stephen H. Kirby, “Taking the Temperature of Slabs,” Nature 403 (2000): 31-34.
  12. Peter D. Ward and Donald Brownlee, Rare Earth (New York: Copernicus, 2000), 191-234.
  13. Katherine L. Moulton and Robert A. Berner, “Quantification of the Effect of Plants on Weathering: Studies in Iceland,” Geology 26 (Oct. 1998): 895-98.
  14. Hugh Ross, Beyond the Cosmos, 2d ed. (Colorado Springs, CO: NavPress, 1999), 217-34.
  15. See Hugh Ross, Probability for a Life Support Body (May 2002), available at

Sidebar: Responding to the Indicators

News of the faint Sun paradox receives scant public attention. In fact, many astronomers and geophysicists know little if anything about it. One cannot help but wonder why.

Carl Sagan was the first to take note of the paradox.1 Sagan, like most astronomers and geophysicists who have studied the paradox, either studiously ignored the philosophical and theological implications with comments such as, “I prefer not to think about it,” or claimed that the paradox must be resolvable through many remarkable but natural coincidences.2

Biologists Lynn Margulis and James Lovelock have championed the “Gaia Hypothesis” as the solution to the faint Sun paradox.3 Margulis and Lovelock make no attempt to deny or ignore the obvious design characteristics. Their response is to deify planet Earth, and in doing so, they exemplify “faith” as current culture and the American Heritage Dictionary, 4th ed., defines it: “Belief that does not rest on logical proof or material evidence.” Earth, they claim, is both an organism and a goddess, working through positive feedback to compensate for the Sun’s increasing luminosity.

Margulis and Lovelock suggest that if Earth’s surface gets warmer, more plants will grow. The growth of more plants will lead to more silicate erosion and possibly more deposition of biological material, both of which will remove carbon dioxide from Earth’s atmosphere. They say this will lead to cooler temperatures, as needed, for Earth’s surface. In this way, Margulis and Lovelock conclude, Earth is fully capable of self-regulating its atmosphere to sustain life indefinitely.

To their credit, Magulis and Lovelock recognize and acknowledge that if the different species of bacteria, fungi, plants, and animals, relative to one another, show up at the wrong times, the wrong places, or in the wrong amounts, the Gaia Hypothesis fails. So, too, if the characteristics of Earth’s orbit, rotation, core, mantle, distribution of continents, or relative abundance of elements were any different. Meanwhile, they express willingness to blindly believe that Goddess Earth guarantees humanity’s survival. They offer no explanation for the supposed Gaia’s source of power, intellect, love and other personal attributes.

Some Christian theists have developed a different response to the faint Sun paradox. Rather than accept the plethora of design evidence it offers, they insist “there is no paradox to explain because the Sun has not been around long enough to increase much in luminosity.”4 In strange fact, they consider the design indicators in the faint Sun paradox too extreme to believe. So, they view the paradox as evidence that the Sun and, therefore, the solar system are young.5

A Reasonable Response

The diversity of responses to the faint Sun paradox testifies to the power of worldview presuppositions. Strict adherents to naturalism treat all phenomena as part of a self-existent, self-organizing, self-perpetuating material realm. They entertain no hypotheses that reach beyond the cosmos and allow no questions—or answers—about ultimate origin, destiny, or meaning. They choose to consider phenomena such as Earth’s adaptation to the increasingly luminous Sun as a series of coincidences, remarkable but random. Carl Sagan seems to have typified this perspective.

An increasing number of scientists (and theologians, too) may be called compartmentalists, separatists, or some other term that describes their worldview assumption that realms of science and spirit either never intersect or need not obey the same rules of logic. On one side of this view stand those who say science demands rigorous application of induction and deduction, while faith flies free on the wings of imagination. Margulis and Lovelock seem to exemplify this perspective.

On the other side of this view are those theists, including some young-Earth creationists, who see science as a flight of fancy and embrace their particular interpretation of the Bible as the singular bedrock of truth.

The worldview shared by a growing number of people—scientists, theologians, and those who are both or neither—requires following the evidence wherever it leads.6 This view presupposes that physical phenomena typically have natural explanations and that the scientific methods used by naturalists can and do lead to reasonable, valid conclusions. However, this view distinguishes between phenomena that simply require more thorough investigation and those that rigorous investigation reveals as the probable handiwork of a transcendent, supernatural Being.

According to the worldview of the latter group, the global warming problem deserves serious attention and thorough investigation, as well as humble supplication for supernatural wisdom.

Sidebar references:

  1. C. Sagan and G. Mullen, “Earth and Mars: Evolution of Atmospheres and Surface Temperatures,” Science 177 (1972): 52-56.
  2. Two of Sagan’s public proclamations of non-theism appear in the close of his Cosmos series for PBS television and in the introduction to Stephen Hawking’s book, A Brief History of Time (New York: Bantam, April, 1988), pp. ix-x.
  3. L. Margulis and J. E. Lovelock, “Biological Modulation of the Earth’s Atmosphere,” Icarus (1974), 471-89; James E. Lovelock, Gaia: A New Look at Life on Earth (Oxford, UK: Oxford University Press, 1979).
  4. Danny Faulkner, “The Young Faint Sun Paradox and the Age of the Solar System,” Creation Ex Nihilo Technical Journal, 15:2 (2001), 3-4.
  5. Faulkner, 4.
  6. 1 Thessalonians 5:21.