An equipotential surface of Earth gravity, including the centrifugal potential, used as an idealized sea-level reference. geoid height responds to long-wavelength density anomalies and boundary deformation; local gravity and geoid height are related but distinct observables.

Infer a spherically averaged density profile using seismic travel times, normal-mode frequencies, mass, moment of inertia, hydrostatic structure and material constraints. Seismic speeds alone measure elastic-modulus-to-density ratios, so they do not uniquely supply density.

Measurement and modeling of a planet’s shape, gravity field, orientation and deformation. Space geodesy can constrain both rigid plate motion and time-dependent solid-Earth loading response.

An geophysicist studies geophysics through mathematical theory, observation or experiment. The field determines the relevant physical systems and measurements, while the individual biographies below connect particular contributions with their scientific ideas.

The planetary crust is the outer compositional rock layer of a differentiated rocky planet. Its thickness need not equal either the lithosphere's thermal thickness or its effective elastic thickness.

The planetary mantle is the predominantly silicate rock region beneath a rocky planet's crust. On geological timescales, solid rock can undergo material creep and support mantle convection without wholesale melting.

The geothermal gradient is the rate at which temperature varies with depth. For steady one-dimensional thermal conduction with constant thermal conductivity $k_T$, the magnitude of upward heat flux is $q=k_{T}dT/dz$.

Publisher of IERS Conventions (2010) by International Earth Rotation and Reference Systems Service.

Genome annotation assigns features and evidence-backed interpretations to a genomic sequence. It can locate genes, repeated elements and regulatory regions, while associating predicted products with possible functions. Structural annotation asks where features lie; functional annotation asks what they do. Both depend on evidence and can change when new data arrive. An apparently missing gene can reflect incomplete assembly or annotation rather than a genuine evolutionary loss. ^[ref]

Genome assembly reconstructs longer genomic sequences from shorter observations, such as sequencing sequencing reads. Overlap and long-range information help order and orient the pieces. Repeated sequences create ambiguity because a read may fit several locations; low coverage can leave gaps. An assembly is therefore an inferred representation with accuracy and completeness limits, and is distinct from genome annotation, which assigns features to that representation. ^[ref]

An assembled genome used as a coordinate system for mapping sequence measurements and comparing genetic variants. A reference is a chosen representation rather than all variation within a species.

Comparative genomics compares genomes to identify shared sequences, lineage-specific changes and differences in genome organization. For example, conservation across related species can help identify a candidate regulatory element or evaluate a predicted gene model. Interpretation depends on shared ancestry and correct correspondence between regions: similarity can reflect gene duplication as well as common species ancestry. ^[ref]

Metagenomics studies genetic material collected from a mixed community, often without first culturing its members separately. DNA sequencing can reveal community composition and potential metabolic capacities. A detected gene indicates sequence potential; its expression and actual contribution to metabolism require additional evidence. Genome assembly from mixed samples is difficult because closely related organisms can share sequences and differ in abundance. ^[ref]

Environmental DNA is DNA recovered from an environmental sample, such as water, soil or sediment, rather than directly from a selected intact organism. It can reveal traces of organisms that were present or contributed material to the sample. Detection depends on shedding, persistence, transport and assay sensitivity, so a positive detection does not alone measure abundance or prove that a living individual is present at that exact location. ^[ref]

The Zoonomia Consortium is a research collaboration using comparative genomics to investigate mammalian biology and conservation. Its comparative resources include aligned genomes from 240 placental mammal species. Comparing many independently diverged lineages helps identify sequence regions that changed unusually little, providing evidence of evolutionary constraint. Constraint is evidence about historical selection; it does not by itself identify the complete function of each conserved base. ^[ref]

Variation in short-repeat lengths resulting from inadequately corrected replication errors, commonly associated with defective DNA mismatch repair.

A repeating sequence of chromosome-end fusion, bridge formation and breakage during division. Inadequate end protection can perpetuate structural changes and copy-number alterations.

A clustered chromosome-rearrangement pattern associated with fragmentation and reassembly. It is one route to complex structural alteration, not a name for every rearranged genome.

Variation in the organization or copy number of genomic segments, including inversions, insertions, deletions and duplications.