Earth's Mass Extinction Cycle & Life's Long History
Nothing seems to strengthen our relationships and beliefs as much as affirmations and confirmations. When I see God supernaturally working in my life or in that of another person, such work persuades me all the more that God exists and cares deeply and lovingly for every human being. Likewise, the study of God's second book of revelation, the book of nature, does much to strengthen my faith in God.
The Bible (God's first book of revelation) promises that the more we learn about the realm of nature, the more evidence we will discover for the handiwork of God (see Job 9:4-10; 12:7-10; Psalms 19:1-4; 50:1-6; 148). It was that biblical principle that inspired the title of my first book, The Fingerprint of God. What I find especially encouraging in my book-writing ventures is finding out about new discoveries that strengthen the points I made regarding the scientific evidence for God.
In my latest book, Improbable Planet (2016), I make several dozen new scientific arguments for the existence and operation of the God of the Bible. Already, some of those proposals have been affirmed by new scientific research findings.
Explaining the Periodicity of Mass Extinctions
One of the more encouraging discoveries comes from two physicists, Eric Kramer and Michael Rowan, at Harvard University. In a paper submitted last fall, they explain the apparent periodicity (regularity) of mass extinction events as recorded in the fossil record.1 As I described in my book, the fossil record reveals not only that numerous mass extinctions of living creatures have taken place on Earth over the past half-billion years, but also that these extinction events have not occurred in a random manner.2 To be specific, major extinction episodes have occurred roughly every 30 million years, as a result of a flurry of comets and asteroids striking Earth. These extinctions have yielded the advanced-life-supporting planet we live on today.
A question to keep in mind is this: If a Creator is responsible for the physics of the solar system and the history of life on Earth, how did he orchestrate events to bring about these extinctions through comets and asteroids?
• The Z-Axis Cycle
In my book I note that a leading explanatory candidate for the mass extinction events is the z-axis cycle in the solar system's orbit around the center of our Milky Way Galaxy (MWG).3 The z-axis cycle refers to the up-and-down movement of the solar system relative to the plane of our galaxy. As the solar system orbits the galactic center, it oscillates up and down relative to the galactic plane in cycles of about 33 million years.
The plane of our galaxy is where the solar system would encounter the greatest density of galactic matter. Encounters with the highest-density parts of the galactic disk could gravitationally perturb the Oort cloud of comets and asteroids.
The Oort cloud (named after Dutch astronomer Jan Oort) is the largest and most distant of the comet-asteroid belts associated with our solar system. When this cloud gets gravitationally perturbed, the probability of a large comet or asteroid impacting Earth rises dramatically. A team of planetary astronomers led by Eugene Shoemaker in 1988 determined that 80 percent of the craters on Earth possessing diameters greater than 100 kilometers, and 50 percent of the craters with diameters greater than 50 kilometers, were caused by long-period comets/asteroids.4 "Long-period" means that it takes the comet or asteroid more than 200 years to orbit the Sun. The Oort cloud is thus the source of virtually all long-period comets/asteroids in our solar system.
• Dark Matter Needed
Figure 1 (below) shows a satellite image of a 100-kilometer diameter impact crater. In their paper, Kramer and Rowan address the question of whether, during the solar system's periodic passages through the plane of the disk of the Milky Way Galaxy, the Oort cloud would be sufficiently disturbed to cause a bombardment of asteroids and comets on Earth, which would, in turn, account for the major mass extinction events in Earth's history.
They first show that a thin disk of dark matter (matter that scientists cannot directly observe) in the MWG is needed to provide an adequate disturbance of the Oort cloud. Second, Kramer and Rowan refer to the Planck satellite maps of the cosmic microwave background radiation (remnants from the universe's beginning) and the galactic background radiation. From the data comprising these maps, they establish that the MWG indeed possesses a thin disk of ordinary dark matter made up of hydrogen gas.5
However, they also show that this disk by itself is not sufficient. The MWG needs an additional disk of "exotic" dark matter (matter made up of particles that interact very weakly or not at all with photons). Next, they demonstrate that the existence of such an exotic dark matter disk is consistent with the observed motions of stars and molecular clouds in the Sun's vicinity.
For this exotic matter disk to have been stable over the past half-billion years of the solar system's history, it must be at least 100 light-years thick.6 Could such a thick disk of exotic dark matter perturb the Oort cloud enough to explain the mass extinction events? In other words, could the disturbance in this solar system belt be sufficient to cause comets and asteroids to rain down on Earth periodically, thereby accounting for our planet's mass extinction events?
In their paper, Kramer and Rowan show that the answer is yes. Another astrophysicist, Nir Shaviv, demonstrated that the oscillatory movement of the solar system through such a disk also explains the 32-million-year climate cycle that geochemists and paleontologists see occurring throughout the Phanerozoic eon (the duration between the Cambrian explosion 543 million years ago and the present).7
• Crossing Galactic Spiral Arms
Kramer and Rowan answer another big question about the mass extinction events. These events look roughly, but far from perfectly, periodic. They point out that another major perturbation of the Oort cloud would occur whenever the solar system crossed a galactic spiral arm. Such crossings occur every several hundred million years.
The physicists go on to show that when the z-axis cycle in the Sun's orbit around the galactic center and the Sun's crossings of the galaxy's spiral arms are both taken into account, the timing of the perturbations of the Oort cloud matches the timing of major impact events on Earth. In particular, the timing of these perturbations correctly predicts the date of the giant comet/asteroid impact event that wiped out the dinosaurs, and with them about 75 percent of all species on Earth 66 million years ago.8
Resolving the Faint Sun Paradox
Although their study is impressive, Kramer and Rowan stop short of explaining the purpose for the apparent periodicity in the mass extinction events in Earth's history. They are silent, too, about design features in the Oort cloud that make advanced life on Earth possible.
As I describe in much detail in Improbable Planet, mass extinction events of a prescribed periodicity and intensity that are quickly followed by mass speciation events play a crucial role in resolving "the faint young Sun paradox."9 This term denotes the enigma of our Sun's having brightened by 18-23 percent throughout the history of life on Earth, while life of any sort could have tolerated, at most, only about a 2 percent change in the Sun's brightness. Figure 2 (below) shows the history of the Sun's luminosity.
Given the actual increase in the Sun's luminosity, there is only one way life could have been sustained on Earth for billions of years with the abundance and diversity necessary to leave behind the wealth of biodeposits that humanity would need to launch and sustain global civilization, and that is for there to have been an incremental drawdown in the quantity of greenhouse gases in Earth's atmosphere. If such drawdown has occurred over the course of Earth's history, then, as the Sun has brightened, the greenhouse effect of Earth's atmosphere has weakened. If the greenhouse gases have been drawn down in the just-right degrees at the just-right times, then the temperatures at Earth's surface have been kept ideal for life in spite of the Sun's progressively getting brighter.
If mass extinction events followed rapidly by mass speciation events occur at a just-right frequency and intensity and at just-right times, life can remain abundant and diverse on Earth for several billion years and thereby provide humans with all the biodeposit resources they need to sustain a high population and advanced civilization. The key here is to periodically remove from Earth life-forms that are less efficient at removing greenhouse gases from Earth's atmosphere and to replace them with life-forms that are more efficient at doing so. Given the rate at which the Sun's luminosity is increasing and the degree to which life can tolerate small changes in the Sun's luminosity, it turns out that the ideal frequency for mass extinction events followed by mass speciation events is—oddly enough—about once every 30-35 million years.
Thanks to the unique and exquisitely designed features of the Sun's origin, position, and subsequent orbit around the center of our galaxy10 and the unique and exquisitely designed features of the Sun's five asteroid/comet belts,11 Earth receives giant impactors of the right size, velocity, and frequency to produce the required mass extinction events. Thanks to the direct interventions of a Creator who knows and understands the physics of the Sun and Earth, the mass speciation events that have followed the mass extinction events have been comprised of the just-right life-forms in the just-right abundance levels at the just-right times to best compensate for the slightly brighter Sun.
As Psalm 104:29-30 proclaims, it is the fate of all life to die off, but God recreates and renews the face of the Earth. Apparently, he does so for the specific benefit of human beings, so that those humans who choose to follow him can quickly take the good news of salvation through Christ to all the people groups of the world. •Hugh Ross
is an astrophysicist and the founder and president of the science-faith think tank Reasons to Believe (RTB).This article originally appeared in Salvo, Issue #41, Summer 2017 Copyright © 2019 Salvo | www.salvomag.com https://salvomag.com/article/salvo41/timing-is-everything