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A sense of time

Nigel Platt (centre) running the London Marathon

Geoscientist 17.4 April 2007

What does a geologist think about as he runs the London Marathon? In geology, you learn about time - a lot of time, says Nigel Platt…

As I look from my window upon the Surrey Downs, I see the Chalk and Greensand hills, walked by pilgrims heading east to Canterbury for eight hundred years and more. That seems a lot of time. But to the Earth, it’s nothing. Our planet is around 4.6 billion years old, give or take a few. That is a lot of time.

A new perspective is required, so let’s imagine the Earth’s own lifetime as a marathon course. The longest journey, but even in this unimaginable race, every 100 million years means just one kilometre in the London Marathon route from Greenwich to The Mall.

If the first half of any marathon is 32 kilometres long, and the second only nine and a half, then the Earth’s journey was much the same. Those early miles are largely lost to her geological biographers, and she has herself all but forgotten them. Only the meteorites’ vague radioactive memory recalls her startline euphoria at the birth of the solar system. Just a few fragments of battered crust in Greenland and South Africa remain to witness the long years of cooling as her race was warming up. The first 10km to the Cutty Sark, were virtually wiped for ever.

And after that, through South London’s streets, it was pretty quiet - for a very long time. Barren, wild, volcanic landscapes rose and were worn away, separated by empty oceans which opened, closed and re-opened unseen throughout long and lonely miles. There was no free oxygen in the air, but we have found microscopic filaments and strange bacteria-like structures in sedimentary rocks around three billion years old. Did these really live, or form as mineral aggregates? A question to fuel a lively debate among geologists; how can we confirm such simple life on distant Mars, when we’re not quite sure what to recognise as "life" at home?

Maybe it was around the 20km mark by Tower Bridge that saw the pattern for Earth’s race set at last. Primitive algae had appeared, forming mounds and crusts to drape those Precambrian shields. They ruled the Earth for 10km more, through Docklands, past Canary Wharf, and into the East End at Poplar. A slow release of oxygen was liberated by their photosynthesis, and a few soft-bodied creatures emerged just past Limehouse, with less than seven kilometres still to race. 

Almost four billion years elapsed - and only slime and worms to show? The pace was hotting up, and our weary Earth was lifted by a sudden crowd as several new groups arose (by the Tower of London) with 5.5km left to run. Among them are many shells like those we find today. But these molluscs and corals would see no fish to swim between them for another long kilometre – since young Nemo’s ancestors can trace their line back only to St Paul’s.

For 38km along her run, Earth’s continents had been all but bare of life - but then the plants appeared. Giant forests rose and fell, leaving coal behind. Flowering species, and insects, graced the land as Earth reached Blackfriars, three kilometres from The Mall. And she was already on Embankment when the supercontinent Pangaea was formed, its vast deserts roamed by giant reptiles, while the Triassic seas ebbed and flowed around its shores.
Soon after, dinosaurs reached their Jurassic peak as the Atlantic Ocean began to open, near Big Ben, with 2km still to go. America drifted west across a widening sea, floored at first by stagnant muds later to form the North Sea oil that I and others seek today.

Sea levels fell again, along Birdcage Walk, as giant rivers and deltas plied the European coast, winnowing the orange tidal sands of Guildford’s golden ford. The encroaching waters then rose once more, as the tiny plankton of a warm Cretaceous sea laid down the Chalk beneath my feet.

The Earth had almost reached Buckingham Palace, 60 million years ago with just 600 metres left to plod, when a middling-sized bolide landed in southeastern Mexico, threatening and in part extinguishing life in Yucatán and across the world. And so the dinosaurs would never live to sprint down The Mall, which honour falls instead to the tiny mammals that survived the global storm.

The next hundred steps see the Downs below my house rise up as gentle folds above a primaeval crustal fault, a far-flung rolling Alpine ripple made as Africa collided with Europe far beyond my Surrey vale. With 30 metres left to run, some man-like hunter apes leave their footprints across a drying African lake shore, shortly before the Ice Age began to rack our northern climes. Those apes’ descendant species were then usurped five paces from the line by Homo sapiens, who invented agriculture one metre from the tape.

The last exultant millimetre of our Earthly race has seen man learn to fly across the atmosphere and beyond, those flights to reach the Moon within my lifetime, which so far spans four ten thousandths of a metre along Earth’s marathon course.

I look again from the window upon my Surrey hill, over this landscape etched by unimaginable time. From the London Massif, across the Weald Basin towards the South Downs beyond. A geologist’s view, to scratch the surface truths of Earth profound.

Nigel Calder, former editor of New Scientist and author of Restless Earth. Author's note: In grateful homage to Nigel Calder’s ‘Restless Earth’, from whose introduction (based on the life of a 46 year-old woman) this piece drew inspiration.