The Past, Present and Eventual Demise of Earth's Driving Force: Plate Tectonics!
- Gabriel Adji
- Nov 24
- 4 min read
The Earth is alive in more ways than you might expect.
Landmasses fracture and drift over millenia.
Mountains crush their way out from the ground.
Compelled by an equal and opposite force, oceans ridges thousands of miles away seal themselves shut.
Plate tectonics refers to the gradual movement of Earth’s lithospheric plates: massive slabs of rock ranging in size from the hundreds to millions of square kilometres. These plates, which include both the crust and the uppermost part of the mantle, float on the ductile, semi-fluid asthenosphere below, shifting slowly over time due to a mix of thermal convection, gravity, and the planet’s internal heat (Palin & Santosh, 2020). Since its formal acceptance in the 1960s , the scientific theory of plate tectonics has revolutionised geology and allowed us to connect countless disparate phenomena together: how mountains form, why earthquakes occur, and where new crust is continuously created and destroyed.
An unlikely birth
Though Earth isn’t the only rocky planet in the Solar System, it’s unique for having seven separate, mobile plates. By chance, our planet has a physical and chemical make-up that allowed for the development of plate tectonics around over 4 billion years ago. This make-up includes adequate internal heat to drive convection, a relatively thin and eggshell-like lithosphere, and most crucially, the presence of water. Water lowers the melting point of rocks and lubricates subduction zones, which are where plate boundaries crush together with enough force to make one slide underneath the other. (Morton, 2017).
The first signs of tectonic activity existed from 4 billion years ago (Morton, 2017), when the primordial Earth had a much hotter mantle. We know this from extensive analysis of greenstone belts; these are ancient metamorphosed volcanic and sedimentary rocks inside Archaean cratons.
Where did other terrestrial planets go wrong? Well, Mars might have once been volcanically active but is too small to retain heat for long, which contributed to a frozen, unmoving lithosphere. Venus’ atmosphere, conversely, is too hot to retain surface water. Both are locked in a ‘stagnant-lid state’, which geologists use to refer to planets with no visible plate boundaries (Stern et al., 2018).
The Present Role of Plate Tectonics
Plate tectonics designed some of the most iconic natural features of our modern world. Think of the Himalayas, the Pacific Ring of Fire, and even the San Andreas fault zone, which moves at over 5 centimeters per year—faster than your fingernails grow!
The San Andreas Fault marks the (violent) intersection of the Pacific and North American Plate
When plates collide, they can drive one slab deep into the mantle, forming subduction zones or sparking chains of volcanoes. Plates can also pull apart at mid-ocean ridges, creating new oceanic crust from rising magma. Elsewhere, plates slide past each other along transform faults and generate destructive earthquakes.
And besides stagnant landmarks, plate tectonics also play a critical role in regulating Earth’s long-term carbon cycle (Palin and Santosh, 2020). The composition of subducting plates contains carbon-rich sediments, which are deposited deep in the mantle. After millions of years, volcanic eruptions will eventually release the carbon again. This keeps atmospheric CO₂ levels in balance over geological time. Without this feedback loop, Earth’s climate and biodiversity would certainly look very, very different.
The End?
But every geologic era must give way to the next. Our planet is gradually losing heat from its core, which is slowing down the very mantle convection which powers tectonic plate motion. Our current models suggest that in one to two billion years, the mantle could cool enough that the lithosphere becomes too rigid to stay as separate plates (Palin and Santosh).
What happens then? Well, without tectonics, mountains will no longer rise. Erosion will slowly flatten continents from the edges. Mid-ocean ridges will go extinct, and ocean basins may shrink as no new crust forms to push them outward. Unfortunately for living organisms, subduction will also cease, which prevents carbon from being returned to the mantle. The ensuing destabilisation of the atmosphere would spell doom for photosynthesizing plants and the animals which depend on them.
Volcanism would taper off, depriving the planet of a key mechanism for releasing internal heat. Over time, Earth could become a geologically stagnant, cratered landscape…a literal “flat Earth” (Hawkesworth et al., 2024).
Plate tectonics has not just shaped the ground we live on, but continually sustains the delicate balance of conditions that allow life to thrive. Our planet’s story began billions of years ago, and will carry on for far longer than we can ever imagine.
References:
Cover image: Jung, C. (2015). Freedom.
Hawkesworth, C., Cawood, P. A., Dhuime, B., & Kemp, T. (2024). Tectonic processes and the evolution of the continental crust. Journal of the Geological Society, 181(4). https://doi.org/10.1144/jgs2024-027
Morton, M. (2017, May 15). When and how did plate tectonics begin on Earth? Www.earthmagazine.org. https://www.earthmagazine.org/article/when-and-how-did-plate-tectonics-begin-earth/
Palin, R. M., & Santosh, M. (2020). Plate tectonics: What, where, why, and when? Gondwana Research, 100, 3–24. https://doi.org/10.1016/j.gr.2020.11.001
Stern, Robert J., et al. “Stagnant Lid Tectonics: Perspectives from Silicate Planets, Dwarf Planets, Large Moons, and Large Asteroids.” Geoscience Frontiers, vol. 9, no. 1, Jan. 2018, pp. 103–119, https://doi.org/10.1016/j.gsf.2017.06.004.
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