Imagine an Earth without plate tectonics. We might envision fewer natural disasters—no tsunamis in India, no earthquakes in Japan, no volcanic eruptions in Iceland. Sounds nice, but it would be more accurate to picture something like the surface of Mars or Venus—barren and hostile to life. Though sometimes disruptive to human civilization, the movement of Earth's crustal plates is vital for creating a hospitable environment. Life requires tectonics—and it turns out that tectonics requires life, too.
Origin-of-life researchers have established that photosynthetic life first appeared 3.83 billion years ago,1 but geophysicists have yet to establish more than a rough date for the origin of plate tectonics. Bit by bit, researchers have uncovered clues to the history of Earth's life-sustaining plate tectonics. The picture they've pieced together reveals that the onset of this globally distributed phenomenon was a gradual process that required carefully orchestrated and well-timed events—including the introduction of distinct life-forms at specified times.
All of this just-right timing and fine-tuning testifies of God's handiwork in designing a planet capable of supporting advanced life.
The Road to Sustained Tectonics
The gradual process leading up to sustained plate tectonics began as early as 3.9 billion years ago when proto-subduction and subduction zone melting began.2 Then, from 3.8 to 3.0 billion years ago, Earth's crust evolved from just a few small isolated plates to a collection of plates, both large and small, that encompassed the entirety of the planet's surface. Crustal slabs altered by subduction began to appear 3.6 billion years ago.3 Recently, researchers analyzed mineral inclusions in diamonds that indicate a compositional shift occurred in the mantle 3.0 billion years ago,4 simultaneous with a major alteration in Earth's geodynamics.5 This shift and alteration mark when plate tectonics became a globally distributed, aggressive, sustained phenomenon.
Studies in geophysics have also revealed that the process of tectonics onset appears finely tuned, with many events helping to stimulate crustal movement. Below are some important examples.
- Three to four billion years ago, higher radioisotope abundances in the planet’s interior raised the mantle's temperature and, thus, lowered the mantle viscosity,6 eventually leading to more frequent breaks in Earth's crust.
- From 3.5 to 3.8 billion years ago, giant asteroids and comets bombarded the planet,7 generating variations in the thickness and density of Earth's crust. These variations resulted in local crustal stresses, which contributed to subduction initiation.8
- Geochemical, petrological, and geological data reveal that Earth's mantle has been hydrated continuously throughout the past 3.8 billion years.9 Therefore, the mantle was much drier 3–4 billion years ago, which helped ignite plate tectonics by lowering the viscosity difference between the crust and the asthenosphere (the mantle's upper 150 kilometers).
- The presence of iron- and sulfur-based anoxygenic photosynthetic life 3.80–3.85 billion years ago led to abundant black shale deposits. Radioisotope decay in these shales—which concentrate heavy radioisotopes, especially those of uranium—produced a high heat flow that, combined with a buoyancy greater than that of seafloor basalts, weakened the crust around the shales.
- About 3.5 billion years ago, the continental nuclei of the Pilbara, Australia, and Kaapvaal, South Africa, cratons ("an old and stable part of the continental lithosphere") formed as thick volcanic plateaus. These cratons generated local dynamic stresses that could have stimulated tectonic activity.10
But among all these factors, one of the most intriguing is life's influence on tectonics. It took abundant life persisting from 3.8–3.0 billion years ago to chemically transform the atmosphere, crust, and mantle sufficiently so that plate tectonics could be sustained at a global level (such as the black shale example above). Only once the continents were fully in place, with abundant life inhabiting both oceans and land, did plate tectonics become sustained.11 (And it will remain sustained until the brightening Sun raises Earth’s surface temperature 60° Centigrade above its present level.12)
Implications for a Creation Model
Why do the first 830 million years of life history look the way they do? One reason, I believe, is because the Creator desired to make advanced life and all preceding life-forms necessary to prepare Earth to accomplish this goal.
Unless life was on Earth as early, as diverse, and as abundant as the planet's physical and chemical conditions would permit, sustained, aggressive, globally manifested plate tectonics would never have been launched as soon as just 3.0 billion years ago. And without plate tectonics, Earth's surface never would have attained the conditions necessary for the survival of advanced life before the Sun became too bright for any thing to survive. Life as diverse and abundant as possible throughout the past 3.0 billion years is also necessary to maintain plate tectonics at sufficiently high levels. But it also takes continued high-level tectonics to sustain life throughout the past 3.0 billion years.
The exacting synergy between life and tectonics throughout the past 3.8 billion years testifies of a Creator who is able to create and maintain just-right life in a just-right environment at just-right times. It also testifies of the magnitude of His care and love for humanity.