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—vary in size, composition, and movement, and have been dragged by convection currents in Earth’s mantle for at least 3 billion years.
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Oceanic plates sink when colliding with less dense continental plates, bending the seafloor into steep depressions that can be almost 11 kilometers deep. Many of Earth’s strongest earthquakes occur at these plate boundaries, often featuring volcanic activity.
Sonar works by sending thousands of sound pulses per second towards the seafloor, capturing the strength and timing of the returning echo. This data can accurately reveal depth, seafloor texture, and the presence of fish habitats to millimeter resolutions.
Instead of a compass needle’s movement indicating a magnetic field, an alternating current produces an oscillating magnetic field in a metal bar. An external magnetic field creates an imbalance in the oscillations, which can be measured quantitatively.
Radiometric dating uses radioactive isotopes to determine the age of objects. By comparing the amounts of parent and daughter isotopes and knowing how long it takes a sample of the former to become the latter, scientists can estimate when an organism was alive or when rocks formed.
Volcanic rocks can lock in the direction of Earth’s magnetic field as they cool, making them natural recorders of magnetism. Dating rocks and seeing the changing orientation of their magnetic field helps construct a timeline of Earth’s magnetic field history.
The symmetry provides evidence of seafloor spreading, where new oceanic crust is created at mid-ocean ridges, which pushes older ocean crust away on either side. Matching the pattern to magnetized material in rocks on Earth’s surface provided a timeline of ocean floor recycling.
Through ridge push, after magma is projected up from the mantle, it cools and sinks, allowing gravity to help push older oceanic crust away. As this crust sinks into the mantle at deep-sea trenches, it pulls on the trailing crust behind it, accelerating ocean crust movement.
Earthquakes and volcanoes are most common at plate boundaries, where moving plates interact. Mapping the locations of these events creates outlines for the different tectonic plates on Earth, whose movements can be tracked via GPS satellites.
At these boundaries, a collision of two oceanic plates produces a curved chain of volcanic islands, like those seen in the Caribbean. A continental-continental plate collision results in plates buckling upward, forming large mountain ranges.
At these boundaries, tectonic plates move apart, stretching and thinning Earth’s crust as long valleys are formed from smaller, interconnected valleys and troughs. Ongoing rifting and erosion can further sink the valley, becoming a rift lake if volcanic activity becomes inactive.
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