Earth’s solid crust, the very ground beneath our feet, can’t be taken for granted. What scientists have been able to learn about our planet’s unique formation history has yielded abundant evidence of Earth’s having been “crafted” for human habitation and civilization.1
Research has revealed, for example, that a strategically designed and strategically timed encounter with a smaller planet dispersed proto-Earth’s thick atmosphere and thousands-of-kilometers-deep ocean, increased the mass and density of proto-Earth, and resulted in the formation of Earth’s large moon.2 The collision between (and consequent merger of) the two planets resulted in Earth’s possessing a large, hot, and dynamic core. This unique core gave rise to Earth’s Goldilocks crust. Earth’s crust is not too thick, nor is it too thin. It is just the right thickness to make possible a long history of life on its uppermost surface and, eventually, global human civilization.3 Now a team of geophysicists has discovered that Earth’s crust is just right for life in several other marvelous ways.
A Clever Analytical Approach While several mysteries concerning Earth’s crust remain, just days before Christmas 2023, a team of geophysicists led by Zhen-Jie Zhang published a breakthrough paper unveiling what researchers had previously considered undecipherable details about Earth’s outer shell of rock.4 Their work brought to light fresh insights that are already yielding dramatic new evidence for design.
Igneous rocks are the product of the cooling and solidification of magma, or lava. Igneous rocks comprise about 15% of Earth’s continents and nearly all of Earth’s oceanic crust. Basalts are the most widespread and abundant of Earth’s igneous rocks. Basalts come from Earth’s asthenosphere.
The asthenosphere is the layer that lies between Earth’s crust and mantle. It is thicker than Earth’s crust but much thinner than Earth’s mantle. Earth’s asthenosphere has an exceptionally low viscosity. Viscosity refers to resistance to stirring. For example, peanut butter is more viscous than syrup and syrup is more viscous than water. The low viscosity of Earth’s asthenosphere lowers the melting point of minerals, explaining why basalts in the asthenosphere are in liquid form and why basaltic rocks are so abundant in Earth’s crust.
Zhang’s team noted that data from various petrologists’ experiments revealed that oxides in basalt primary melts (basalts that have suffered little or no chemical alteration since cooling and solidifying from their molten form) are sensitive to the pressure of melting but show little or no sensitivity to the chemical compositions in either the asthenosphere or the upper mantle. They then explained how this property of basalt primary melts combined with measurements of oxides in the basalt primary melts could be used to determine the thickness of Earth’s lithosphere at the location and age of the basalt sample. (The lithosphere constitutes Earth’s crust plus that part of Earth’s upper mantle that does not move, relative to the crust.)
So, Zhang and his colleagues then supervised a machine-learning algorithm to analyze global geo-databases (e.g., EarthChem and GEOROC) of basalts. By this means they were able to determine ongoing, cyclical variations in the thickness of Earth’s crust throughout the past 3.8 billion years.
Three Discoveries Come to Light First, Zhang’s team’s analysis revealed that a supercontinent forms as Earth’s crust thickens, and it breaks apart when Earth’s crust thins. At its thickest, Earth’s crust averages a depth of 140 kilometers, while at its thinnest, a depth of about 70 kilometers, on average. Zhang’s team also observed a slight trend: the minimum thickness becomes thinner with each succeeding supercontinent cycle. During the most recent cycle, the average crust thickness declined to 60 kilometers. At present, the average thickness is 72 kilometers.
Second, the team’s study revealed that five supercontinent cycles have occurred during the past 3 billion years, with a periodicity that averages about 0.6 billion years, and that the duration of each supercontinent decreases with each progressive cycle, shortening from 0.50 billion years to 0.12 billion years (see figure).
Figure: Supercontinents in Earth’s Past History The bars indicate the varying durations of Earth’s supercontinents. Data credit: Zhang et al.; Figure credit: Hugh Ross
Third, and most importantly, Zhang’s team established that there has never been a “stagnant lid” regime in Earth’s history—a time when the crust was a single stationary plate. Zhang and his colleagues determined that Earth’s crust has always consisted of multiple plates constantly moving relative to one another. In other words, during the entire time in which stable solid rock features have existed on Earth’s surface, plate tectonic activity has been ongoing. Plate tectonics has endured throughout the past 3.8 billion years. This research result thereby confirms the conclusions of a study, published in 2020, based on the buildup of argon isotopes in Earth’s atmosphere.5
How Plate Tectonics Impact Life, and Vice Versa What particularly caught my attention as I read the paper published by Zhang’s team is that the duration of plate tectonics on Earth appears identical to the duration of life on Earth. Both began at the same time and have continually persisted throughout the past 3.8 billion years.
This simultaneity is unsurprising when we recognize that life’s persistence on Earth requires sustained plate tectonic activity to recycle the nutrients life requires. At the same time, however, the persistence of plate tectonics at the level this recycling demands depends upon the existence of an abundance of iron- and sulfur-based anoxygenic photosynthetic life. These microbes play a crucial role in producing the black shales that facilitate the tectonic motion.
Black shales are more buoyant than seafloor basalts. Black shales also contain high concentrations of heavy radioisotopes, especially uranium-235 and uranium-238. Radioisotope decay in the black shales generates heat. This heat combined with the shales’ greater buoyancy destabilizes the adjacent crust. This weakening facilitates the sliding of one tectonic plate past an adjacent plate or the sliding of one tectonic plate underneath an adjacent plate.
For advanced life to be possible, a long history of microbial life must precede it. For Earth’s surface environment to become chemically ready to support the flourishing of plants and animals requires at least 3 billion years of preparation by a huge abundance and diversity of microbial life. Even more time is required to permit the existence of human beings.6
Thus, for humans to exist on Earth, life’s origin must have occurred no later than 3.8 billion years ago. Likewise, plate tectonics must have begun no later than 3.8 billion years ago, which means Earth must have cooled sufficiently from its merger with the rocky planet Theia7 no more recently than 3.8 billion years ago. This simultaneity and precise timing and design testifies of exquisite orchestration.
One More “Aha!” Zhang and his colleagues add in the concluding paragraphs of their paper that “Earth was eventually primed for the arrival of a colorful Phanerozoic with the Cambrian explosion of metazoans.”8 In other words, the team noted that the sudden explosion of multiple animal phyla with intestinal tracts, circulatory systems, and complex internal and external organs—an event known as the Cambrian explosion—depended on a dramatic acceleration of the crustal thinning that initiated a supercontinent breakup. How so?
The breakup of Gondwana generated massive landslides into the seas (the Great Unconformity), producing vast continental shelves that brought about the chemical transformation and oxygenation of Earth’s atmosphere and seas. This relatively rapid sequence of events created for the first time in Earth’s history an environment fit for advanced life. Thus, it made possible the Avalon and Cambrian bursts of life just early enough to make way for the future existence of human beings. A more thorough explanation of these events and their meticulous orchestration can be found in Improbable Planet,9Designed to the Core,10 and Rescuing Inerrancy.11 Each new discovery points to the work of a supernatural, super-intelligent Creator who intended for us to be here and to recognize his handiwork.
Zhen-Jie Zhang et al., “Lithospheric Thickness Records Tectonic Evolution by Controlling Metamorphic Conditions,” Science Advances 9, no. 50 (December 15, 2023): id. eadi2134, doi:10.1126/sciadv.adi2134.
Meng Guo and Jun Korenaga, “Argon Constraints on the Early Growth of Felsic Continental Crust,” Science Advances 6, no. 21 (May 20, 2020): id. eaaqz6234, doi:10.1126/sciadv.aaz6234.
