Nature knows no nostalgia

Strange Worlds: Edition I

Welcome. This the first edition of a new series here on Cosmographia — Strange Worlds. For the full map of posts, see here.

The Titan's Goblet — Thomas Cole (1833) Public Domain.

Homo sapiens are a new addition to this world. Recorded history — some five millennia — is but a blink in the 300,000 years of our species. So little is known about even our own deep time that recently discovered bones among the Moroccan sands set back the prehistory of our kind a whole 100,000 years — our time roaming the Earth was a full 50% longer than we realised. Broadening our scope to all human species, including Neanderthals, Denisovans, and Homo habilis, the entire history of our genus extends back only 2.8 million years. Considering that life first began 3.8 billion years ago, our genus has only walked the Earth on its two legs for 0.07% of the time elapsed since the first prokaryotes made the jump from folded proteins to living organism.

As such, our perceptions of our home planet are warped by recency bias. We know of seven continents, frozen poles, and five major oceans, but it was not always so. Over the last couple of centuries, developments in palaeontology, geology, and paleoecology have increasingly revealed a world that in its different epochs has donned many guises. As little as 13,000 years ago the shifting sands of the Sahara were instead covered in a lush grassland; rivers carved verdant valleys through Antartica 14 million years ago; India spent 53 million years as an island, enough time to evolve its own weird and wonderful species of life. Our sense of place is so inextricably bound up with flora and fauna — African savannah, rainforest in the tropics, Siberian taiga — that the idea that these landscapes are as temporal and fleeting as their inhabitants violates our sense of the world.

Dig deep enough into soil and rock, and one can find the last remnants of strange and forgotten worlds. Beneath the roads and buildings of modern Britain, for example, one can find the bones of enormous cave lions, crocodiles, and a species of shaggy-haired rhinoceros. The rolling hills of English countryside are a new phenomenon: for most of the history of life on Earth, grasses, which currently make up 30% of all plant life now living, didn’t exist. How strange is it to think that herbivorous Diplodocus never set eyes on a flower, which only evolved after the lumbering giant went extinct? In the oceans of aeons past, it was not coral who formed reefs, but molluscs. Spiders once spun their webs in a world without trees.

These curious landscapes that covered the Earth only a brief time ago would be deeply unfamiliar to us — alien even. So, let’s explore them.

In Strange Worlds, we’ll be venturing down into the dry and dusty depression that once joined Europe and Africa into a single landmass; we’ll be roaming across strange supercontinents that have long ceased to exist; and we’ll peer nervously at the large and terrifying megafauna that once ruled the Earth and its seas.

But first, let’s start at the beginning.

There are two forces that shape the topography of our planet: rock and water.

Rock was there from the beginning, when part of the swirl of dust and gas orbiting the early Sun first began coalescing into our planet. Though long believed to have arrived later, via cascading planetesimals, icy gloms of cosmic dust, it seems that some water may have formed from outgassing of the early mantle. Much of this water, perhaps enough to fill an entire ocean, would have been lost to space — a process still ongoing today, but much easier back when the Earth was less massive. Any remaining water would have been vaporised along with the outer layer of crust when another world wrecked into ours in a cataclysm that saw the Earth’s surface blaze into an inferno that raged for 100 million years. When it finally cooled, the rains came.

Around 4.4 billion years ago, the ocean of liquid magma on the Earth’s surface began to cool. Iron-rich rocks hardened first, then a lighter crust of zircons formed — some of which still exist today in Canada, Greenland, and Australia. As the Hadean aeon (named after Hades, Greek god of the underworld) gave way to the Archean (from arkhē, ‘beginning’), rain began to fall from the sky for the first time. It was a downpour like no other.

Rain fell day after day after day, weeks turning to months, years into decades, centuries into millennia. Water pooled in depressions to become lakes. It seeped into the ground forming aquifers and underground rivulets. Water poured overland forming trickles, streams, and then the mighty torrents of the world’s first rivers. It flowed down, down, always down, into great basins to become seas and oceans. As it moved, slowly but surely, the water began to shape the world of rock.

The tectonic movements of the Earth’s crust can create new continents, split them asunder, or thrust them together. They can raise mountains, belch flame and ash into the sky, create and destroy new land at will. But even the most hardened of rock is not immune to water’s power. Bit by bit, the first streams loosened and carried away grains of minerals, or dissolved them into their waters. They weathered even the tallest mountains, split open canyons, dug deep grooves into the surface of our planet. Wherever the tectonic movements created new depressions, water rushed in to fill the gap; wherever they raised new heights, water ground them down again. When at last the rivers reached their journey’s end in lakes or seas, the sun’s warmth lifted them up into the atmosphere again, beginning the cycle anew.

Only a few hundred million years after this battle between rock and water first began, bluey-green cyanobacteria, the earliest photosynthesisers, began releasing the world’s first breaths of oxygen into the atmosphere.

Life had begun.