“Diamonds are a girl’s best friend.” So the song goes, but the processes that created these gems, namely earthquakes, have not generated such lyrics. Understandably, many people fear earthquakes and wish they would never happen.

This contrast—the love of diamonds but hatred of earthquakes—is actually a great irony. We humans can easily live without diamonds. We cannot, however, live without earthquakes.

The Vital Importance of Earthquakes (Tectonics)
Earthquakes are part of Earth’s plate tectonic activity. Earth’s crust is currently divided into about 8 major plates with surface areas greater than 40,000,000 square kilometers and 16 minor plates with surface areas greater than 1,000,000 square kilometers.1

These 24 plates float above Earth’s mantle. Thanks to Earth’s interior being super-endowed with uranium and thorium, the radioactive decay of this uranium and thorium heats up the mantle sufficiently to make it soft and viscous. Consequently, Earth’s tectonic plates bump into and slide against one another. Where deep water is present at a boundary between two plates, one plate can slip underneath another plate and be thrust into the mantle.

During Earth’s infancy, water covered the entirety of Earth’s surface and all Earth’s plates were made up of basalts (igneous rocks). Tectonic activity gave rise to plate subduction which resulted in some of the basalts being chemically transformed into silicates. Silicates are lighter than basalts and hence float above the basalts. Eventually, sufficient silicates formed for landmasses to begin appearing above the water’s surface.

The combination of Earth’s water cycle and the exposure of silicates above sea level initiated the silicate-carbonate cycle. Rain falling on the exposed silicates acted as a catalyst to generate chemical reactions, including a net reaction where carbon dioxide is removed from the atmosphere to transform silicates into carbonates and sand. The gradual removal of carbon dioxide, a greenhouse gas, from the atmosphere means that as the Sun gets progressively brighter (see figure) Earth’s atmosphere progressively traps less of the Sun’s heat. This compensation for the Sun’s brightening has allowed Earth’s surface temperature to remain suitable for life for a long time period. To word it differently, without an operating silicate-carbonate cycle, life could not remain on our planet for long.

Figure: Sun’s Luminosity throughout Its History
Image credit: Hugh Ross

The silicate-carbonate cycle delivers other crucial benefits. Nearly impenetrable silicate is converted into easily penetrable carbonates and sand. This conversion allows for advanced vegetation, plants in particular. The carbonates and sand also store water for the vegetation and plants. A benefit for humans is that industrially useless silicates are transformed into industrially valuable carbonates and sand. For example, carbonates and sand are the most important ingredients in concrete. Advanced civilization would be unimaginable without concrete, and concrete would not exist without an operating silicate-carbonate cycle.

Additional crucial benefits from plate tectonic activity include the distribution of life-critical nutrients to parts of the planet that otherwise would receive none, the recycling of those same nutrients throughout the planet’s surface environments, and the creation of extensive bedrock water storage systems2 on the continental landmasses. Plate tectonic activity also regulates how much ocean water gets subducted into the crust and mantle and how much is returned to Earth’s surface through geysers and volcanic eruptions.3 Without this finely tuned regulation of the quantities of water in the oceans, crust, and mantle, advanced life could not exist. Hence, earthquakes, though frightful in many respects, confer indispensable benefits to life.

Earthquakes and Diamonds
As the remains of once-living organisms are driven into Earth’s mantle through tectonic plate subduction, some of the carbon in that organic material becomes exposed to heat and pressure extreme enough to transform the carbon into diamonds. The rise of mantle plumes brings some of those diamonds into Earth’s crust. So, without plate tectonic activity, “girls” (women) would need to find other best friends and men would need to look elsewhere for engagement rings.

Diamonds can last for what seems forever, but plate tectonic activity will not. Earth’s tectonic activity is governed by heat flow from Earth’s interior. There are two major sources of this heat flow: radioactive heat from the decay of uranium and thorium isotopes and relic heat left over from the accretion of interplanetary dust and planetesimals that resulted in Earth’s formation. Both the radioactive heat and the relic heat have gradually subsided since the birth of Earth.

When Earth was young (during its first 750 million years), the high heat flow from Earth’s interior produced thick oceanic crust.4 At that time, water covered all of Earth’s surface. Hence, all of Earth’s crust was oceanic crust. Thick oceanic crust made subduction tectonics virtually impossible.

Today, heat flow from Earth’s interior is barely adequate to melt the upper mantle at plate boundaries so that one plate can subside (slide) underneath another. Within several million years from now, subduction tectonics will begin to decrease at an accelerating rate. In less than a billion years from now, all tectonic activity on Earth will cease.

Earth’s tectonic history can be seen as five periods, the first of which began with a 750-million-year era called the stagnant lid (hot stagnant lid regime). This was followed by 750 million years of intermittent subduction tectonics and then by 3 billion years of sustained tectonic activity. This third period effectively compensated for the Sun’s increasing luminosity while recycling nutrients for life and building up the biodeposits needed for global human civilization. The next period, our current one, has been marked by declining tectonic activity that soon will fail to compensate for the Sun’s increasing luminosity. The fifth and final period will feature a permanent stagnant lid (referred to as a cold stagnant lid regime).5

Civilization and Purpose
A 3-billion-year period of strong, sustained tectonic activity is remarkable. In my book, Improbable Planet, I explain why Earth is very likely alone in possessing such a long period of strong tectonic activity.6 That we are near the end of such a long period of sustained, strong tectonic activity implies that humans were purposely placed on Earth at the best possible time to build up a huge population. We also were placed here at the only possible time where we could exploit Earth’s vast biodeposits to launch and sustain global, high-technology civilization—and enjoy some jewels along the way. It is thanks to that civilization that we can fulfill one of the major purposes for why God created us. It allows humans to spread the message of God’s existence and character, of what troubles humans, and of how God promises to redeem those who place their trust in him.

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