Deep Time | Kaelan

Earth is about 4.54 billion years old.¹ Put that span into 24 hours and the non-avian dinosaurs, lost 66 million years ago, die out around 11:39 p.m.² Homo sapiens, present for about 300,000 years, arrives in the last six seconds.³ Five thousand years takes about a tenth of a second. The clock is an analogy, and its answer changes when its dates change.

James Hutton developed a cyclic theory of Earth in the 1780s. At Siccar Point in 1788, tilted rock beneath younger horizontal layers gave him strong field evidence for repeated deposition, uplift, and erosion.⁴ His 1788 paper ends, “no vestige of a beginning,—no prospect of an end.”⁵ The line states the reach of his model; modern geology gives Earth an age.

Deep time is hard to picture. John McPhee offered one scale in Basin and Range: spread your arms to stand for Earth history and human history fits within one stroke of a nail file at the end.⁶ The image helps with proportion. It does not make the number more exact.

Recorded human history covers a small fraction of Earth’s age. Over longer spans, mountains rise and erode, continents move, and species appear and vanish. The scale changes which effects a decision can reach; it does not decide whether a human concern matters.

People use “Anthropocene” for the scale of human change to Earth. It is not a formal epoch. In March 2024, the International Commission on Stratigraphy approved a vote that rejected adding it to the geologic time scale.⁷ The word remains useful as an informal term.

Human-made radionuclides, plastics, concrete, and changes in atmospheric chemistry can leave geological signals.⁸ Which signals survive for millions of years, and what a future geologist could read from them, remains uncertain. Current species-extinction rates are estimated at tens to hundreds of times the average over the past 10 million years.⁹ That is an unfolding loss, not proof that a sixth mass extinction has already matched the five past events.

Deep time joins two facts. Human lives occupy little geological time. Human actions can still alter systems that outlast the people who caused the change. The first fact does not cancel the second.

At a personal scale, memento mori asks how to use a finite life. Deep time asks a different question: which choices can affect people and ecosystems far beyond that life?

Go Deeper

Books

Annals of the Former World by John McPhee — Four books on American geology, Pulitzer Prize. McPhee’s metaphors make deep time feel real.
Time’s Arrow, Time’s Cycle by Stephen Jay Gould — Intellectual history of how we learned to see geological time.
The Clock of the Long Now by Stewart Brand — An argument for thinking beyond one lifetime.

Essays

James Hutton’s “Theory of the Earth” (1788) — An early cyclic account of Earth’s history.
“The Anthropocene: conceptual and historical perspectives” by Will Steffen et al. (2011) — Defining the human epoch.

Places

Siccar Point, Scotland — Field evidence that helped Hutton argue for repeated geological cycles.

Sources

U.S. Geological Survey, “Geologic Time: Age of the Earth”. ↩
U.S. National Park Service, “Dinosaurs”. ↩
Smithsonian Human Origins Program, “Homo sapiens”. ↩
Edinburgh Geological Society, “Hutton’s Unconformity — Siccar Point”. ↩
James Hutton, “Theory of the Earth”, 1788, 304. ↩
John McPhee, Basin and Range (Farrar, Straus and Giroux, 1981), 126. ↩
International Commission on Stratigraphy, “Anthropocene Working Group”, 26 March 2024. ↩
Will Steffen and colleagues, “Stratigraphic and Earth System approaches to defining the Anthropocene”, Earth’s Future 4, no. 8 (2016), 324–345. ↩
Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, “Global Assessment Report on Biodiversity and Ecosystem Services”, 2019. ↩