Nicolas Steno
Sedimentary layers are laid down flat, with younger ones on top (superposition). He also showed 'tongue stones' were fossil shark teeth.
Why it matters: The basis of reading rock layers as history.
π Steno N. De solido intra solidum naturaliter contento. Florence, 1669.
James Hutton
At Siccar Point, tilted old layers beneath flat young ones showed cycles of deposition, uplift and erosion needing immense time.
Why it matters: Earth is vastly old; founded the rock cycle idea.
π Hutton J. Theory of the Earth. Trans. R. Soc. Edinburgh 1 (1788).
William Smith
Mapped the rock layers of England, Wales and part of Scotland, using fossils to match layers across the country.
Why it matters: Fossils as markers of age; the start of geological mapping.
π Smith W. A Delineation of the Strata of England and Wales. London, 1815.
Charles Lyell
Argued that processes we see today, working over long times, shaped Earth (uniformitarianism).
Why it matters: Hugely influenced Darwin, who took volume 1 on the Beagle.
π Lyell C. Principles of Geology, 3 vols. London, 1830β33.
Richard Dixon Oldham
Earthquake records showed waves slowed or blocked at depth β evidence for a core.
Why it matters: First seismic look inside the planet.
π Oldham RD. Q. J. Geol. Soc. 62:456 (1906).
Bertram Boltwood (after Rutherford)
Used the decay of uranium to lead to date rocks at hundreds of millions to billions of years.
Why it matters: Gave numbers to deep time.
π Boltwood BB. Am. J. Sci. 23:77 (1907).
Andrija MohoroviΔiΔ
A sudden jump in seismic-wave speed marks the base of the crust.
Why it matters: Defined the crustβmantle boundary.
π MohoroviΔiΔ A. Jahrbuch des meteorologischen Observatoriums in Zagreb (1909).
Alfred Wegener
Proposed the continents were once joined in Pangaea and have drifted apart, using coastlines, fossils and rocks.
Why it matters: Right idea, but rejected for 50 years for lack of a mechanism.
π Wegener A. Die Entstehung der Kontinente und Ozeane. Braunschweig, 1915.
Beno Gutenberg
Placed the coreβmantle boundary at β 2,900 km depth β very close to today's 2,891 km.
Why it matters: Measured the size of the core.
π Gutenberg B. Physikalische Zeitschrift 14:1217 (1913).
Charles Richter
A logarithmic scale for earthquake size (each step β 32Γ more energy). Today the moment magnitude scale (Kanamori, 1977) is used.
Why it matters: Made earthquakes comparable.
π Richter CF. Bull. Seismol. Soc. Am. 25:1 (1935).
Inge Lehmann
Faint P-waves arriving where none were expected showed a solid inner core inside the liquid outer core.
Why it matters: Completed the basic picture of Earth's layers.
π Lehmann I. Publications du Bureau Central SΓ©ismologique International A14:87 (1936).
Clair Patterson
Lead isotopes in meteorites gave an age of 4.55 billion years β still accepted (4.54 Β± 0.05).
Why it matters: Earth's age, settled. (His work also led to banning leaded petrol.)
π Patterson C. Geochim. Cosmochim. Acta 10:230 (1956).
Harry Hess
New ocean floor forms at mid-ocean ridges and spreads outward; old floor sinks back at trenches.
Why it matters: Supplied the mechanism Wegener lacked.
π Hess HH. History of ocean basins. In: Petrologic Studies, GSA, 1962.
Fred Vine & Drummond Matthews (also Lawrence Morley)
Symmetric stripes of normal and reversed magnetism on either side of ridges record sea-floor spreading.
Why it matters: The decisive evidence for spreading.
π Vine FJ, Matthews DH. Nature 199:947 (1963).
J. Tuzo Wilson
Identified a new class of faults where plates slide past each other, linking ridges and trenches.
Why it matters: Completed the set of plate boundaries.
π Wilson JT. Nature 207:343 (1965).
McKenzie & Parker; Morgan; Le Pichon
Described Earth's surface as rigid plates rotating on a sphere, explaining earthquakes, volcanoes and mountain belts.
Why it matters: The unifying theory of geology.
π McKenzie DP, Parker RL. Nature 216:1276 (1967); Morgan WJ. JGR 73:1959 (1968).
Luis & Walter Alvarez and colleagues
A thin clay layer rich in iridium at the end of the Cretaceous pointed to an asteroid impact; the Chicxulub crater was identified in 1991.
Why it matters: Showed sudden catastrophes also shape Earth's history.
π Alvarez LW et al. Science 208:1095 (1980); Hildebrand AR et al. Geology 19:867 (1991).
Simon Wilde and colleagues
A 4.4-billion-year-old zircon from Jack Hills, Australia, hinted at liquid water on very early Earth.
Why it matters: Pushes back the record of Earth's crust.
π Wilde SA et al. Nature 409:175 (2001).
Many institutes
The sea floor off Japan moved up to β 50 m; the tsunami killed nearly 20,000 people. GPS and sea-floor sensors recorded it in unprecedented detail.
Why it matters: Reshaped hazard planning worldwide.
π Simons M et al. Science 332:1421 (2011).
NASA InSight lander
A seismometer on Mars (2018β2022) recorded over 1,300 marsquakes and measured the Martian core.
Why it matters: Geology's tools now work on other planets.
π StΓ€hler SC et al. Science 373:443 (2021).