Geoscience Reference
In-Depth Information
bard. They set up survey stations and measured outcrops; they climbed cliffs, collected samples, and
steadily filled in the blank map of Svalbard's geological history.
And as Brian returned to the islands time and again, one particular feature of the rocks began to
bother him. In many of the outcrops that poked through Ny Friesland's sheath of ice, a strange red
stripe stood out against the pale yellows and browns and greys around it. Up close, the stripe was a
chaotic mix of reddish boulders and rocks, all shapes and sizes, bound together in a background of
fine silt.
Brian had known this pattern all his life. He'd grown up in Scarborough, on the North Yorkshire
coast of England, and as a child he would collect the alien stones that studded the cliffs there—the
famous “boulder clays”. The boulders embedded in Yorkshire's sea cliffs were an unmistakable signal
that ice had been on the move. They had arrived fresh from Scandinavia, where glaciers had dragged
them off the land and dumped them into the North Sea.
Glaciers don't just glide serenely over a surface; they grind into it. A glacier scratches and scours
the bedrock with the boulders it drags along. It bulldozes yet more rocks ahead of its advancing ice
front. The surface of a glacier can be littered with debris that has tumbled off the steep cliffs at the
sides and is carried along with the slowly moving ice. Eventually the glacier will spill into the sea.
Perhaps it will break off into chunks of iceberg that gradually melt and deliver their load of rock debris
to the seafloor as individual “dropstones”. Perhaps it will simply offload its rocks just a little way off-
shore. Glaciers dump similar rock jumbles on land, but land deposits tend to be eroded away by the
action of wind and rain, and most of the really old ice rocks that have survived around the world were
formed in the protected environment of a shallow sea.
That's exactly what had happened to create Brian Harland's mysterious red stripe, and he was
baffled by it. Why should he be troubled by signs of glacier deposits in frigid Svalbard? Because he
already knew that in Precambrian times, Svalbard was very much warmer than it is today. He was sure
that when the rocks of ancient Svalbard formed, conditions there were positively tropical.
They must have been, he reasoned, because most of the rocks in the outcrops he was studying were
tropical. They were carbonates, pale grey and yellow rocks made of the same stuff as seashells. These
rocks, though, were born before shells even existed. Unlike the chalks and limestones formed in more
recent times from the crushed shells of sea-creatures, these carbonate rocks had nothing to do with
the presence of living things. Instead, they had formed from a purely chemical process in Precambrian
seawater, and then rained down on to the seafloor to be compacted into rock.
And here's the important point: this process happens only in warm seas. Cold water clings to its
carbonate; only warm water releases it. That's why carbonate platforms hold up the sunny islands of
the Caribbean. You'll find them beneath the Great Barrier Reef, and throughout the islands of Indone-
sia. And you'll also find them on either side of Brian's icy red stripe.
What's more, in the carbonates below his red stripe, Brian found oolite, a strange type of rock
made up of tiny spheres that are squashed together like petrified caviar. This bizarre texture is also
utterly characteristic of tropical climates. Six hundred million years ago, the islands of Svalbard had
clearly been hot. Finding signs of ice among oolitic carbonate rocks was bizarre, like watching a gla-
cier march across Barbados.
Brian began to investigate further. How about northern Norway? There, too, he found Precambrian
carbonates interrupted by a layer of ice rocks. Greenland? The same. Now he began to pore over
published papers, marking out anywhere in the world where geologists had mapped ice rocks in the
Precambrian, the mysterious geological period that was devoid of distinguishing fossils. They were
everywhere. Every single continent had the clear traces of ancient ice.
