I finally understood evolution. No joke.
I always knew about evolution, and I never doubted it. Yet I still found it miraculous that a pile of inorganic matter, after billions of years of evolution, became us — beings with consciousness. Then I learned about the White Cliffs of Dover.
Thirty stories high, stretching for 13 kilometers of continuous white cliff.
Yes, you read that right: the cliffs are made by living things.
A Cliff Built by Single Cells
About 70 million years ago, what is now southern England was a shallow sea.
The surface teemed with a single-celled marine alga called coccolithophore. Each one is a single cell — but it builds itself a beautiful shell of calcium carbonate. The shell is not one solid piece: it is assembled from many tiny, ornate discs called coccoliths.
When these tiny creatures died, the process ran:
coccolithophore → calcium carbonate shell → sink to the seafloor → white ooze → compaction → lithification → today's chalk → the White Cliffs of Dover
A single coccolith is only about 3–5 μm across. To picture it: the diameter of one human hair spans dozens of coccoliths side by side.
The sediment accumulated at just 0.5 millimeters per year. Yet it produced a biomineral structure on this staggering scale.
And the cliffs are nothing special — they are only visible because they were uplifted and exposed. This rock is called chalk, a sedimentary rock. By now you have guessed it: chalk gave the Cretaceous its name. There was so much of it that it named an entire geological period.
Behind evolution lies countless rounds of reproduction, competition, elimination and death. Ruthless natural selection preserves the genetic variations that fit the environment better.
Standing in front of the cliffs, looking at the corpses of marine plankton smaller than a hair's width, piled 110 meters high — that is when you viscerally feel how much death happened here.
And the Cretaceous was already a thriving age of life.
Older Still: Banded Iron Formations
You may ask: were there earlier biominerals? By the Cretaceous, Earth already hosted giants like Tyrannosaurus rex and Triceratops. The answer: yes — the Banded Iron Formations (BIF).
They are spectacular.
The early ocean held vast amounts of dissolved Fe²⁺ (ferrous iron). As certain microbes — especially photosynthetic, oxygen-producing ones — grew in importance, oxidation converted Fe²⁺ into insoluble iron minerals, which settled to the seafloor. This was the Great Oxidation Event, about 2.5 billion years ago.
Over hundreds of millions of years, the deposits built up:
black/red iron layers + gray-white chert layers
Alternating, layer after layer, until they formed enormous iron formations.
Many of the world's giant iron ore deposits are, in essence, geological relics of microbes changing the global chemistry of the planet 2.5 billion years ago. Not all iron ore is BIF — the share is about 60%. But that means the majority of global iron resources are BIF-hosted.
Evolution Is a Funnel
Put plainly, evolution is a giant funnel: every step forward is paid for with vast amounts of death and extinction. The scale is simply beyond ordinary comprehension — which is why evolution feels abrupt.
When an ordinary person stands before the cliffs and sees that a small wave from the Cretaceous ocean solidified into 110 meters of rock, they can finally feel real awe and understanding of evolution.
And consider this: the car that carries you to the cliffs is made of steel that is a gift from microbes 2.5 billion years ago. The fuel is the remains of algae and plankton from hundreds of millions of years ago.
So we drive steel bequeathed by ancient life, burn the sedimentary remains of ancient life, and arrive at cliffs built from the corpses of countless organisms — while the "I" that can gaze at all of it and understand it is itself a short-lived fruit of four billion years of evolution.
The Tree of Life, With the Mass Extinctions Shown
Let me end by sharing an evolutionary chart I have treasured for a long time. It is stunning.
