Good morning. It's Tuesday, Sept. 30, and we're bringing you the latest Science & Technology newsletter. Every week, we provide fascinating deep dives into the worlds of physics, chemistry, biology, geoscience, computer science, and more.
This week, we're covering plate tectonics. The unifying theory of geology represents our best explanation for much of the geological activity we observe on Earth's surface and helps us better understand the inner workings of our planet.
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— Marco Machado, 1440 Science and Technology Editor |
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Background
The theory of plate tectonics explains that the majority of Earth’s geological features—from mountain ranges to ocean trenches—result from interactions between slabs of rock that make up Earth’s outer shell.
The slabs—collectively called tectonic plates—range from the size of Oklahoma City to as large as 20% of the planet’s surface area (learn about them). The plates are dragged, on average, about as fast as fingernails grow by material moving beneath them in Earth’s interior.
Differences in plate composition, movement direction, and interactions when they meet have produced continuous large-scale changes to Earth’s surface for at least 3 billion years (watch visualization).
Early Evidence
While scientists saw that Africa and South America seemed to fit together since cartographers mapped the latter in the late 1500s (see history of world maps), it was not until 1912 that German meteorologist Alfred Wegener developed a scientific basis for landmass movement called continental drift.
He proposed that all continents existed in a supercontinent, Pangaea, over 200 million years ago. The theory explained why similar rock layers, plant and animal fossils, and glacial deposits were found on unconnected continents (see evidence).
However, Wegener could not explain what caused the drifting of material that was seen as solid rock and faced criticism from colleagues until he died in 1930 (learn more).
A year later, English geologist Arthur Holmes published a paper describing how continents could move via mantle convection—currents that transfer heat from radioactive decay and matter throughout Earth’s mantle (watch visualization).
Seafloor Spreading
Advances in reconnaissance technology designed to search for submarines during World War II, including sonar and fluxgate magnetometers, were used by scientists after the war to map the ocean floor.
Instead of the expected flat plains, scientists observed underwater mountain chains tens of thousands of kilometers long. Earthquakes and volcanoes were common in these mid-ocean ridges, and rock samples taken from the ocean floor showed that their ages increased with distance from the ridges.
The ocean floor at equally long deep-sea trenches was as much as six times deeper than the Grand Canyon. The oldest underwater rocks were found here, but were only about 180 million years old—far less than the oldest rocks that made up continents, which were over 4 billion years old (radiometric dating, explained).
Scientists knew Earth’s magnetic field had flipped multiple times after observing crystallized lava on the surface (watch explainer). Matching flips were observed in ocean floor rocks, but in symmetric patterns on either side of mid-ocean ridges.
In the early 1960s, American geophysicist Harry H. Hess proposed the theory of seafloor spreading to explain these observations.
As magma rises from Earth’s mantle, ridges are pushed apart and downhill, creating a gap that the magma fills and cools to become new, young rock. Like a conveyor belt, ridge push continuously displaces older rock toward trenches, where it sinks beneath less dense continental rock back into the mantle.
Alongside ridge push, the weight of the sinking rock can pull the rest of the trailing plate faster into the mantle—a mechanism known as slab pull. Both ridge push and slab pull vary based on the size and composition of plates, producing the different speeds at which tectonic plates move (see visualization).
Plate tectonics emerged as a unifying theory of continental drift, mantle convection, seafloor spreading, and earthquake and volcano locations outlining plate boundaries (see maps).
Geological Activity
Plate boundaries—convergent, divergent, and transform—are where plates meet and produce the majority of geological features we see on the planet’s surface.
At convergent boundaries, different combinations of colliding continental and oceanic plates create volcanoes, island systems, mountain ranges, and about 80% of the world’s earthquakes (explore examples).
Besides mid-ocean ridges, divergent boundaries can create rift valleys as plates move apart (see examples).
At transform boundaries, plates slide horizontally past one another, causing them to deform or fracture rather than destroy or form new rocks (learn more). |
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Scientific theories are tested explanations for why certain phenomena occur |
Laws, such as Newton’s law of gravity, describe what occurs based on many observations—usually through a mathematical relationship—without explaining why what is observed occurs. Robust theories provide these explanations, but don’t ever become laws. Learn distinctions between theories, laws, hypotheses, and facts here. |
The discovery of the Mid-Atlantic Ridge was initially dismissed as ‘girl talk’ |
Marie Tharp identified the structure when mapping the ocean floor using sonar data, but her colleague, who did not favor continental drift, was unconvinced. Famed filmmaker Jacques Cousteau even tried to disprove her work with underwater footage, only to validate her maps. Learn more about her work here. |
The cycling of carbon via tectonic activity may have facilitated life on Earth |
Plates sinking into Earth’s mantle pull carbon from the surface, helping stabilize the atmosphere and climate by removing greenhouse gases from volcanic eruptions. At the same time, magma is a significant contributor of heavy metals and other crucial minerals for life to the surface. Learn more about the research here. |
A supercontinent may have triggered a global ice age 750 million years ago |
Before Pangaea, Earth’s continental plates had drifted together and broken apart multiple times, with each event altering atmospheric CO2 concentrations and triggering climate change. The continents are estimated to come together again in 50 million to 250 million years. Learn how we might prepare for it here. |
Stagnant lids found on Mercury, Mars, and the moon prevent tectonic activity |
Unlike Earth’s lithosphere, which is composed of plates dragged by convection, the outer shells of observed terrestrial bodies in the solar system are not exposed to sufficient stress to be pulled apart. Earth is expected to develop a stagnant lid in about 1.45 billion years. Learn more about geologically dormant worlds here. |
Explore a simulation of plate tectonics |
You are given a planetary model with optional rock formation and your choice of the number of tectonic plates and their densities. Draw continents, assign forces and plate boundary types, and run the simulation across map types to observe earthquakes, volcanoes, and other geological activity. Play with the simulation here. |
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Like all great scientists, we love spending time researching the latest scientific breakthroughs, tech releases, engaging explainers, and the connections between science and society that are making headlines. Here's what we found this week.
> Exploring the role of painkillers, vaccines, and genetics in autism
The New York Times | Emily Baumgaertner Nunn and Azeen Ghorayshi. Amid discussions about associations between vaccines and acetaminophen use with autism, learn what research says about them and the role of genetics. (Read)
> Developers of 'griefbots' reflect on their creations
Nature | Tammy Worth. Advancements in AI technology have resulted in the appearance of several platforms that engineer AI versions of people who have passed away, providing individuals a new means of processing their loss. (Read)
> An EV battery breakthrough can lead to recharging cars in 15 minutes
ZME Science | Mihai Andre. Scientists from the Korea Advanced Institute of Science and Technology have identified a workaround for overcoming internal short-circuiting that had previously prevented lithium-metal battery effectiveness. (Read)
> JUNO, the world's largest neutrino detector, is now live
ScienceAlert | Andy Tomaswick. The Jiangmen Underground Neutrino Observatory will spend at least a decade trying to catch these elusive particles as they travel through a pool of ultrapure water surrounded by 43,212 photodetectors. (Read)
> World's oceans have crossed critical acidity threshold
The Guardian | Jonathan Watts. The transgression represents the seventh of nine planetary boundaries surpassed in the Institute for Climate Impact Research's annual report, jeopardizing species throughout ocean food chains. (Read)
> Assessing impact of AI on early-career employment
IEEE Spectrum | Gwendolyn Rak. Data from the US' largest payroll provider shows that roles for software engineers between 22 and 30 years old have been most susceptible to AI replacement since their widespread adoption in late 2022. (Read) |
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"The Earth, instead of appearing as an inert statue, is a living, mobile thing." |
—John Tuzo Wilson, Canadian geologist and geophysicist |
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