Why do stars twinkle? Why does God sometimes seem silent? Some “why” questions are more elusive than others.
When presented with RTB’s biblical creation model people often ask, “If God designed the Earth and its life to provide a home for humans, why did he waste so much time with bacteria?” This question arises from the new strong evidence that early bacteria, every bit as advanced as bacteria today, and dating back 3.5 – 3.9 billion years, remain the only detectable life forms on Earth until 2.3 billion years ago. Until about 0.8 billion years ago, bacteria maintained the status of Earth’s predominant life form. It appears to some that God was negligent, disinterested, or incompetent in preparing Earth for humanity.
No one can claim to understand all God’s reasons for waiting a billion and a half years to create anything on Earth besides bacteria. The conversion of poisons into metal ores offers one positive outcome.1 Another possible answer to the question comes from recent studies demonstrating that cyanobacteria (photosynthetic bacteria) take much longer than previously thought to pump oxygen into Earth’s atmosphere.2 In previous studies, researchers simply calculated how efficiently cyanobacteria produce and expel oxygen. They did not take into account how efficiently Earth’s crust and mantle absorbed the oxygen.
New calculations from geophysical modeling reveal that the crust and especially the mantle of the early Earth were rich in reducing minerals.3 These reducing minerals acted as a sponge, soaking up much of the oxygen in their vicinity. However, like a sponge, the earth could only soak up so much. Mantle material breaking through the Earth’s crust came into contact with whatever oxygen cyanobacteria had thrust into the atmosphere, reacted with it, and consequently lost some of its reducing strength. Over time, the quantity of reducing minerals in the mantle slowly diminished whereas the quantity of oxidizing minerals slowly increased.
Models demonstrate that between 3.9 billion and 2.7 billion years ago, reducing minerals in the mantle and crust mopped up almost all the atmospheric oxygen produced by cyanobacteria. Between 2.7 and 2.2 billion years ago, gases released from volcanic activity had lost much of their reducing capacity. From 2.2 billion years ago until the arrival of large oxygen-breathing animals (0.54 billion years ago), the oxygen level in the atmosphere slowly rose.
The rise in atmospheric oxygen did not immediately pave the way for advanced life. The increased atmospheric oxygen first stripped the air of methane. Though early Earth’s atmosphere probably contained only a small amount of methane, that small amount efficiently trapped heat from the Sun. Heat-trapping was critical for primordial life since the early Sun was about 35% dimmer.4 At 2.2 billion years ago, the Sun was 20% dimmer than it is today. The removal of methane from Earth’s atmosphere led to a few snowball events—ice ages during which snow and ice covered virtually the entire surface of the planet.5 The last such snowball occurred just before the Cambrian explosion. At the Cambrian explosion, 543 million years ago, advanced, large body-size life forms began to appear.
We don’t always have the privilege of knowing “why” God does things. Yet, little glimpses into his ways reassure us of his great power and love.
- Hugh Ross, “Bacteria Help Prepare Earth for Life,” Connections 3, no. 1 (2001), 4.
- Jon Copley, “The Story of O,” Nature 410 (2001): 862-64.
- Copley, 864.
- James F. Kasting and David H. Grinspoon, “The Faint Young Sun Problem,” in The Sun in Time, eds. C. P. Sonett, M. S. Giampapa, and M. S. Matthews (Tucson: University of Arizona Press, 1991), 447-50; see FACTS for FAITH 10 (Q3 2002) “The Faint Sun Paradox,” for more information on this dynamic.
- D. A. Evans, N. J. Beukes, and J. L. Kirschvink, “Low-Latitude Glaciation in the Paleoproterozoic,” Nature 386 (1997): 262-66; P. Hoffman, A Kaufman, G. Halverson, and D. Schrog, “A Neoproterozoic Snowball Earth,” Science 281 (1998): 1342-46; Peter D. Ward and Donald Brownlee, Rare Earth (New York: Copernicus, 2000), 112-22.