Thinking in Geological Time

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We’re terrible at comprehending deep time. Our brains evolved to understand days, seasons, maybe a human lifetime. But geology asks us to stretch our imagination across billions of years.John McPhee coined the term “deep time” in his 1981 book “Basin and Range” — it’s become the standard way geologists talk about Earth’s vast history.

The Calendar Analogy

Here’s a way to visualize it: compress Earth’s 4.5 billion year history into a single calendar year.

• January 1st: Earth forms from cosmic dust
• February: The first oceans appear
• March: Life begins (single-celled organisms)
• November: First multicellular life
• December 10th: First animals appear
• December 26th: Dinosaurs emerge
• December 30th: Dinosaurs go extinct
• December 31st, 11:36 PM: First humans appear
• December 31st, 11:59:46 PM: Recorded human history begins

All of human civilization fits into the last 14 seconds before midnight.

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Deep Time Changes Everything

When you truly grasp the timescales involved, it reframes how you see the world:

Mountains Aren’t Permanent

The Himalayas are “young” at 50 million years old. They’re still growing, rising millimeters each year as India collides with Asia.Mount Everest grows about 4mm per year — roughly the rate your fingernails grow!

The Appalachians? They were once as tall as the Himalayas, formed 480 million years ago. Time and erosion have worn them down to gentle slopes.

Mountains rise and fall like waves on a slow-motion ocean.

Continents Drift

Pangaea — the supercontinent — broke apart just 175 million years ago. Before that, there was Rodinia. Before that, Columbia. Supercontinents form and break apart in cycles roughly every 500 million years.

The Atlantic Ocean is widening by about 2.5cm per year. In 100 million years, it’ll be unrecognizably different.

We’re Living in an Ice Age

Wait, what? Yes — technically, we’re in an interglacial period of the Quaternary Ice Age, which began 2.6 million years ago.During the last glacial maximum (20,000 years ago), ice sheets covered most of Canada and reached as far south as New York City. The fact that we have permanent ice at the poles means we’re in an ice age.

Most of Earth’s history has been much warmer, with no ice caps at all.

The Fossil Record: Time Made Visible

Every fossil is a window into deep time. When you hold a 400-million-year-old trilobite fossil, you’re touching a creature that lived when:

• There were no trees yet
• Fish had just evolved jaws
• The first tetrapods were crawling onto land
• All continents were arranged completely differently

Why This Matters

Understanding deep time isn’t just geology — it’s perspective.

• The planet has been through dramatic changes before
• Life is incredibly resilient (and fragile)
• Human timescales are a blink of an eye
• Change is the only constant
• Nothing on Earth's surface is truly permanent

When you think in geological time, you realize that the “permanent” features of our world — mountain ranges, ocean basins, species — are all temporary. Everything is in motion, just very, very slowly.

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Learning to See Deeply

Next time you see a rock outcrop, try to read it. Each layer is a page in Earth’s history book. That sedimentary rock? Ancient seafloor. Those tilted layers? Tectonic forces. That unconformity? Millions of years missing.

The Earth is constantly writing its autobiography. We just need to learn to read it.

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Recommended: John McPhee’s “Annals of the Former World” — incredible writing about geology and deep time.