Today’s New Reason To Believe

by Jeff Zweerink

Earthquakes and volcanos serve as important reminders of the phenomenal forces at work underneath Earth’s surface. The shape and arrangements of the continents change as the massive tectonic plates float across the more fluid upper mantle. This tectonic activity changed the initial, water-covered state of Earth, covering roughly 30% of the planet with continents. Additionally, it replaces continental landmass lost to erosion.

Every few hundred million years all the continents group together to form supercontinents such as Pangaea and Rodinia. Eventually, these supercontinents split up and start a new cycle of continental drift that eventually forms a new supercontinent.

While an abundance of geological data records the motions of the continents over time, scientists have struggled to model such behavior in the lab. However, two New York University scientists have recently built a model that demonstrates cyclic behavior analogous to the recorded continental drift. Their model includes a high-viscosity glycerin/water mixture with heavier-than-water plastic beads (which play the role of continents). The model is heated and cooled in a way reflective of processes operating inside Earth.

When the model was heated and cooled in the absence of the beads, the glycerin/water mixture flowed in a circle for long periods of time without change. Upon adding the beads, the circulation pattern reversed directions every few hours. Thus, they conclude that the continents play a critical role in the cyclic building of supercontinents. The thermal mass associated with the continents affects the flow of rock in the underlying mantle, causing it to change directions periodically. Previous thinking assumed that continents simply rode along on the flow of mantle rock.

Without the flow reversal, the supercontinent would never split apart to begin a new cycle and plate tectonics would eventually grind to a halt. While this change would eliminate earthquakes, the loss of tectonic activity would also rapidly (on geological timescales) lead to an uninhabitable Earth. This research provides scientists with another tool for exploring how well-designed Earth’s interior processes support life.

by Jeff Zweerink

Imagine the Antarctic glaciers extending over the whole Earth. Dating back to the early 1960s, scientists proposed just such a scenario, known as a “snowball Earth” hypotheses to explain various geological and geochemical data in the planet’s history.

According to the proposal, a snowball Earth could possibly form when the planet experiences periods of increased glaciation (or ice ages) due to variations in its orbit around the Sun. As Earth’s temperature drops, glaciers around the north and south poles begin to grow and spread toward the equator. Snow and ice reflect more sunlight than rock, vegetation, and water, causing a further decrease in the global climate. If the glaciers reach close enough to the equator, the increased cooling might result in the complete covering of Earth with glaciers.

During the Cryogenian geological period (850-630 million years ago), two extensive glaciations occurred which may have resulted in snowball Earth. Presumably, continued volcanic action produced enough greenhouse gas emissions to reverse these hypothesized snowball Earth conditions. A thick glacial covering would dramatically impact life on Earth. In fact, these two extensive glaciations immediately preceded the Cambrian Explosion. However, if an abundance of organic carbon sediments covers the ocean floors, then a mechanism exists to prevent snowball scenarios.

An article published in Nature describes the discovery of one preventive mechanism. As the global temperature decreases with the advance of the glaciers, the oceans dissolve more oxygen from the atmosphere. Consequently, this oxygen reacts with the buried organic carbon to produce carbon dioxide, which then enters the atmosphere. The resulting increase in greenhouse heating prevents the further advance of the glaciers.

Because abundant life has existed for about 3.5 to 3.8 billion years of Earth’s history, an ample supply of deep ocean organic carbon has always existed to prevent a snowball Earth. While the snowball Earth hypotheses remain debatable, they do highlight a few apologetic points.

1. A snowball Earth provides one more mechanism that can severely disrupt a planet’s capacity to support life.

2. Scientists continue to find evidence that Earth’s habitability relies on an intricate interplay of geological (glaciation), astronomical (variations in Earth’s orbit), and biological (abundant deep-ocean organic carbon remains) processes.

Both of these points attest to the difficulty, from a naturalistic perspective, of attaining conditions suitable for life. That Earth has remained habitable throughout most of its history comports well with the idea that a super-intelligent Designer fashioned Earth intending to fill it with life.

by Jeff Zweerink

Last Christmas, my family flew back to the midwest in a Boeing 737. Getting an airplane to stay up in the air requires a tremendous amount of design, but most of the flight delivers all the excitement of a long bus ride. The action usually occurs during the takeoff (and to some extent, the landing).

New geophysical discoveries show similar action for the tectonic history of Earth. Plate tectonics requires three essential processes to operate. First, rigid continental and oceanic plates must float and move around on the more fluid upper mantle below. Second, hot magma from the mantle must well-up through cracks that form as the plates move apart. Third, where the plates collide with one another, one of the plates must move below the other, back into the mantle, in a process called subduction. Scientists largely understand the mechanisms of the first two steps as well as how subduction functions. However, the initiation of subduction remains more enigmatic.

As described in Science, recent research demonstrates that Earth’s tectonic activity fluctuated significantly in the past because the subduction zones shut down (as a result of continental plates coming into contact). In particular, the time period when the Rodinia “supercontinent” formed corresponds to a dramatic decrease in subduction. (On a side note, when subduction reinitiated leading to the break-up of Rodinia, Earth experienced a glaciation which covered almost the entire globe.) Most of the current subduction zones reside in the Pacific Ocean. Consequently, the closing of the Pacific basin in roughly 350 million years will bring another period of tectonic inactivity.

As continental plates collide, subduction inevitably terminates. However, such a process does not necessarily lead to subduction initiating somewhere else. For example, the Indian and African continents collided with Eurasia 35-50 million years ago, shutting down a subduction zone (this collision caused the formation and continued growth of the Himalayas—home to Mount Everest). Yet since the collision, no new subduction zones have formed in the region nor does it appear that any will.

Most scientists assumed that plate tectonics operated slowly and continuously over the bulk of Earth’s history. But new scientific results argue for an “on-again/off-again” tectonic past. Because of the importance of subduction initiation for plate tectonics activity, RTB’s creation model predicts that scientists will find substantial fine-tuning as they better understand this critical process.

(As an added bonus, a more sporadic nature of Earth’s plate tectonic activity also solves another long-standing geological problem. Scientists measure the tectonic activity and the rate at which heat escapes from Earth today. Extrapolating those two quantities just two billion years in the past leads to an unacceptably high interior temperature for Earth. However, if tectonic activity experienced periods of stagnation, heat would escape more slowly in the past compared to extrapolations from the measured values assuming continuous plate tectonics. Extrapolations incorporating intermittent tectonic activity give reasonable temperatures all the way back to Earth’s formation.)

Going back to the plane analogy, sustaining flight necessitates a high degree of fine-tuning on the part of the pilots and the engineers of the aircraft. Air travel requires an even greater amount of fine-tuning because planes must take off and land—without a successful takeoff, no one can go home for the holidays. Similarly, without subduction initiation the life-essential process of plate tectonics would never take off on Earth.