Earth system
How we know
Almost nothing in this corpus was observed directly. Each conclusion about the deep Earth is the end of a chain of reasoning that starts with an instrument at the surface — and the chain is recorded alongside the conclusion.
Everything below the shallowest crust is reconstructed from waves recorded at the top. Seismology is the instrument that reaches, and the reason interior claims in this corpus carry inferred rather than observed status.[1, 2]
The reasoning is often about an absence. Shear waves cannot cross a liquid; they stop appearing beyond about 103 degrees from an epicentre; therefore the outer core is liquid. Nobody saw a liquid core — they saw a missing signal.[1, 2, 3]
Methods have limits, and the limits are part of the knowledge. Tomographic images have finite resolution; radiometric dates record a resetting event rather than an origin; some particles are simply below what a detector can see.[1, 2, 3]
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How we know what is inside Earth
No one has seen the mantle, and no one ever will. Everything below the shallowest crust is reconstructed from waves recorded at the surface — which is why the interior chapters of Earth science are written in the language of inference, not observation.
Dating the Earth
Radiometric dating is precise, well understood, and does not measure what people usually think it measures. Understanding what it actually records explains why the age of the Earth had to come from meteorites.
Methods
The techniques through which Lithoen’s subjects are known, each carrying its own principle and its own documented limitations.
Scientific method
Seismology
The study of seismic waves generated by earthquakes and other sources. Because the waves travel through the whole planet and change character at every boundary they cross, seismology is the principal means by which Earth’s interior is known at all.
Scientific method
Seismic tomography
Reconstruction of three-dimensional variations in seismic wave speed within the Earth from very large numbers of wave observations. It produces images of the mantle, but they are model reconstructions with finite resolution, not photographs.
Scientific method
Radiometric dating
Determination of numerical ages from the decay of long-lived radioactive isotopes in rocks and minerals. It dates the last time a sample was melted or sufficiently disturbed, which is why the age of a rock and the age of the Earth are different questions.
Scientific method
Geoneutrino detection
Measurement of antineutrinos emitted by radioactive decay inside the Earth. Because geoneutrinos pass through the planet almost unaffected, they carry information about deep radiogenic heat production that no other method can reach.
Scientific method
Marine magnetic surveying
Measurement of magnetic variations across the sea floor. Because ocean-floor basalt records the polarity of Earth’s field as it cools, these surveys turned the sea floor into a record of its own formation.
Scientific method
Geomagnetic field modelling
Representation of the observed geomagnetic field as a mathematical model — typically a spherical-harmonic expansion valid for a defined epoch — separating contributions from the core, the crust and external currents.
What they reach
Subjects that exist in this corpus only because a method reaches them. None has been sampled.
Earth layer
Inner core
The solid innermost region of Earth’s core. Its solidity is an inference from the behaviour of seismic waves rather than a direct observation, and the reasoning behind that inference has itself been revised.
Earth layer
Outer core
The liquid part of Earth’s metallic core. Its inability to transmit shear waves is the observation from which its liquid state is inferred, and motion within it generates Earth’s main magnetic field.
Earth layer
Mantle
The dense, hot layer of semi-solid rock between the crust and the core, containing more iron, magnesium and calcium than the crust. Its slow internal motion is central to plate tectonics.
Earth layer
Asthenosphere
A relatively narrow, mobile zone in the upper mantle beneath the lithosphere, composed of hot material that can soften and flow over geological time. The rigid plates are thought to move over it.
Geological process
Mantle convection
Slow circulation of the solid mantle driven by internal heat, in which hot material rises and cooler, denser material sinks. The geometry of that circulation is far less well constrained than the fact of it.
Models as products
A model is not a lesser kind of knowledge — it is a kind that declares its own validity window.
Dataset
World Magnetic Model
A mathematical model of Earth’s main magnetic field, issued for a five-year epoch and revised as the field changes. It is a worked example of a model that is authoritative precisely because it is explicitly a model with a stated validity window.
Geological process
Seismic wave propagation
The travel of elastic waves through the Earth. Compressional (P) and shear (S) waves behave differently in solids and liquids, and it is that difference which reveals the state of Earth’s interior.
Hub last updated 2026-09-06. Every entry above is a structured record; the bracketed references link to the entities whose claims support each statement.