A Bright Young Sun
Caltech astrophysicists Juliana Sackmann and Arnold Boothroyd have achieved a breakthrough. In spring 2003, they unveiled a new and more accurate model for the Sun’s life cycle, a model that addresses and may help resolve “the faint Sun paradox.” This new model has significant implications for God’s involvement in life’s origin on Earth—as well as for the subsequent history of life, including human life.
Sackmann and Boothroyd see evidence that the Sun started off with 4 to 7 percent more mass than it has today.1 This extra mass translates into a significantly brighter Sun in its earliest days. (A star’s luminosity is proportional to the fourth power of its mass.) A brighter Sun means a warmer Sun, and warmth is what astronomers have been looking for since discovering that the Sun was fainter in the past—some 25 percent less luminous, according to the old model—near the time of life’s origin.2 To account for the heat that sustained early life, they had relied heavily on the presence of extra “greenhouse gases,” such as ammonia and/or methane, in early Earth’s atmosphere.
According to this new model, the Sun was at its peak mass early, prior to its 40 millionth year. From that time until it was about 1.0 to 1.5 billion years old, it gradually shed some of that mass and grew dimmer. At 1.0 to 1.5 billion years old, the Sun reached its dimmest point and stopped shedding mass, and from that time onward the Sun has gradually grown brighter and brighter as its hydrogen burning has progressed. (Solar burning converts hydrogen into helium, the extra helium leads to more efficient hydrogen burning, and more efficient burning yields a brighter sun.)
When hydrogen fusion burning first ignited (4.52 billion years ago), the Sun would have been no less than 90 percent and possibly as much as 105 percent its current brightness, says the new model. At the time of life’s origin on Earth (approximately 3.8 billion years ago) the Sun would have been only 14 to 16 percent less luminous than it is today, as compared with 25 percent less luminous in the old model. From 3.0 billion years ago to the present, the two models are essentially the same.
If the Sun began with greater mass, early Earth’s atmosphere would not require the quantity of powerful greenhouse gases such as methane and ammonia for warmth at the time of life’s origin. In fact, it would require no methane or ammonia at all. This lack of dependence on ammonia and methane seems critical for explaining life’s stability, abundance, and diversity on early Earth since both ammonia and methane are problematic. They are very difficult to produce in Earth’s atmosphere and extremely unstable. Lessening the dependence on such greenhouse gases to sustain adequate temperatures for life allows for greater temperature variation over Earth’s surface. (The greater the quantity of greenhouse gases, the less temperature variation is possible in Earth’s atmosphere.) Greater temperature variation accommodates a wider diversity of bacterial life in the era when life began.
Increasing the diversity, abundance, and stability of life on Earth previous to 3 billion years ago serves to speed Earth’s preparedness for humans and human civilization. This speed is important since Earth and the Sun can only sustain human civilization for a relatively brief period in which just-right conditions, including solar stability, prevail.
Astronomers’ discovery of a brighter, younger Sun speaks of God’s intricate and optimized design in preparing Earth for life, and especially for humanity’s life—and quality of life. Furthermore, it demonstrates that the advance of science, the development of new and better models, sustains rather than negates the case for faith in the biblical Creator.
For more discussion of Sackmann and Boothroyd’s discovery readers can access the February 18, 2003 Creation Update Web cast.
- Juliana Sackmann and Arnold I. Boothroyd, “Our Sun. V. A Bright Young Sun Consistent with Helioseismology and Warm Temperatures on Ancient Earth and Mars,” Astrophysical Journal 583 (2003), 1024-39. Astronomers observe that solar-sized stars throughout this galaxy lose significant mass during their infancy and youth. Sackmann and Boothroyd also note that old lunar rocks and old grains from meteorites show evidence for a much more intense solar wind (the mechanism for solar mass loss) 3 to 4 billion years ago.
- Hugh Ross, “The Faint Sun Paradox,” Facts for Faith 10(Q3 2002), 26-33.