This is Westeros as it exists in the days of tumult, in the days following the death of King Robert Baratheon, in the shortening days that warn that winter is coming.  But this is also the geological history of Westeros, reaching far deeper through the annals of time than the reign of any of the Seven Kingdoms.  We pieced this geologic history together from character observations, town names, official Game of Thrones maps, and the principles of geology learned here on Earth.  Using only limited data we were able to reimagine 500 million years of planetary evolution, including volcanoes, continents rising from the oceans, and ice ages (with guest appearance by white walkers and dragons).  To explore the history, and to view our maps of the geologic reconstructions, click the numbered icons on the map, or on the links below. Continue reading The Geology of Game of Thrones →

From the texts, we know that the kingdoms have persisted for thousands of years, with many kings rising and falling as the tides (though we won’t concern ourselves with kings or kingdoms here).  From the same texts and carefully surveyed maps, we also know that Westeros contains mountain ranges, hot springs, granite, gold mines, deserts, ice walls, and red, grey, and black stones used to construct castles.  To the carefully trained eye – admittedly trained here on Earth – each of these elements betrays a rich and complex geologic history of the continent, reaching back over 500 million years.

We began with a simple question: what is the size of the Game of Thrones planet?  After all, understanding processes at the planetary scale is crucial to geology.  Past researchers have attempted these calculations without consideration of the coupled system of climate and geology, and these are essential initial attempts.  We started with the most basic of observations: it is cold enough in the north to maintain the Wall of ice that shields the continent from the White Walkers, and it is warm enough in the south that the maps are colored as deserts, an environment encountered most recently by the Khaleesi, Daenerys Targaryen, at approximately the same latitude on Essos.

On Earth, deserts appear within a general latitude range, with most near 30° north (for example, the Sahara in Africa) and south (for example, the Atacama desert in South America).  This is due to circulation of atmospheric Hadley cells.  The harsh cold of the north, and the presence of the Wall for millennia, suggests that the Wall is at or near the Arctic Circle, currently at 66.5° north latitude on Earth.  So we have some approximate bounds for Westeros, stretching from 30° to 66.5° latitude, and all of it likely on the northern hemisphere.  Finally, we have it on good authority that it is 3,000 miles from the Wall to the southern flank of the continent, the deserts of Dorne.  Using simple geometry, we calculate that the radius of this dragon-inhabited planet is 4,297 miles, slightly larger than Earth’s radius of 3,959 miles, but still remarkably similar.  Fortunately for us, this won’t be the last time we assume similarities between this planet and our home on Earth.

Twenty-five million years ago (Mya), a line of fire and molten rock cut through the planet’s crust – like Wildfire cut through the ships at Blackwater Bay – and separated the previously joined continents of Westeros and Essos.  This spreading ridge is analogous to the mid-Atlantic ridge that was largely responsible for the breakup of Earth’s last super-continent of Pangaea.  The most striking evidence of this breakup is the morphological similarities of the shores of Westeros and Essos, appearing as though they could fit together as pieces of some geological jigsaw puzzle (similar to Alfred Wegener’s, and others’, observation that South America and Africa seemed to fit in the same way).  Based on the average spreading rate of the mid-Atlantic ridge (~2.5 cm/yr), we calculate that the rifting between Westeros and Essos began around 25 Mya.

Furthermore, we propose that the Mountains of the Moon and the Hills of Norvos all belong to the same range, preferentially eroded in the east for reasons unknown (more on this later).  Also intriguing is the fact that the Hills of Norvos do not follow the same southwest-to-northeast trajectory as the Mountains of the Moon.  We cannot say for certain the orientation of the fault that created these ranges, but if they once befell a more linear path, then we can surmise that the Hills of Norvos have rotated in a clockwise direction, indicating that the rift between Westeros and Essos began in the north, and effectively “unzipped” to the south.  As of this writing, we cannot say with any certainty what caused the rifting (note: such radical changes in plate motion and the type of faulting can be found in Earth history, but generally require 100s of millions of years to come about, nearly 10 times longer than the process appears to have taken on this planet).

Perhaps the most controversial of our assertions is that plate tectonics are actively transforming the surface of Westeros, indeed the entire planet, and have done so for eons.  Yet the very presence of mountain ranges, a breathable atmosphere, and even life itself suggest that active tectonics must be considered in all analyses of Westeros.  Plate tectonics is the fundamental principal by which we understand Earth’s geology.  Among many others, tectonics explains how continents move, how rocks help regulate the atmosphere, and how earthquakes shake the ground and volcanoes ignite the skies.  Given active tectonics, we are somewhat troubled by the lack of earthquakes and volcanoes throughout the Seven Kingdoms.  While we cannot be certain, it is possible that the faulting responsible for creating the mountain ranges has since stopped, or at least slowed to a point when the recurrence intervals of large earthquakes and/or volcanic eruptions is long enough to circumvent the written records.  Though, at the moment, this remains speculation.

The salt of the Salt Shore, almost certainly an evaporite deposit, suggests that the region south of the Red Mountains, known as Dorne, was once submerged beneath a shallow sea.  Some time in the past, sea level was lower as glaciers trapped water as ice.  As sea level fell, a large depression, like the mouth of a leviathan, isolated itself from the adjacent ocean.  The result was an entrapped body of briny water exposed to the solar radiation (or perhaps to the heat of dragon’s breath, as we are unsure of the evolutionary history of dragons).  Over time, the sea began to evaporate away, leaving the salt behind (similar to the Bonneville Salt Flats near Salt Lake City, Utah).  The age of these deposits is somewhat difficult to constrain.  Evaporite deposits tend to form in hot, arid environments.  As previously mentioned, desert environments tend to form near 30°.  As will be discussed in the forthcoming sections, Westeros has gradually moved north throughout its evolution.  Given this tectonic drift, we speculate that the Salt Shore deposits are approximately 30-40 million years old.

Additional geologic evidence supports this apparently brash claim of entire sea boiled away by the sun (or, again, dragons).  If town names are to be trusted as geologically accurate (a dubious, but necessary assumption), then we can infer the presence of green sandstone at the island of Greenstone.  Greenstone is a generic and generally unhelpful term, as it can apply to sedimentary or metamorphic rocks.  Combing through references to greenstone on Earth yielded a hit in the United Kingdom, where greenstone refers to sandstone contaminated with emerald-hued micas that was deposited within a shallow sea.  The geographic proximity of two separate rock types, greenstone and salt, consistent with shallow sea deposition strengthens the notion of a long lost sea.  The final piece of evidence comes from the town of Sandstone (guess which rocks we assume are there).  While sandstone can form in a variety of environments, we interpret these sandstones as deltaic, forming as rivers flowing from the Red Mountains reached the shallow sea and deposited their sediment load.

It was a land of ice indeed.  Forty million years ago, a giant ice sheet, likely over a mile thick, covered nearly two-thirds of Westeros, and extended as far south as 40° north latitude, just shy of King’s Landing.  This ocean of ice would have dwarfed the great Wall (similar to the ice sheet that covered much of North America during the last ice ages).  To understand this land of ice, it is important to recognize the distinction between “greenhouse v. icehouse” planetary conditions and “glacial v. interglacial” conditions.  The former describes conditions that vary on time scales of millions of years or longer (like snowball Earth, nearly 650 Mya), while the latter generally describes climate variability on time scales of millions of years or less (like the last ice age, during the Pleistocene).  While the data is sparse, we propose that 40 Mya, this planet experienced icehouse conditions that created the massive ice sheet.  While it is currently unknown, the reanimation of hominoid biota currently north of the Wall may be a local indicator that appears concurrently with glacial cycles.  This area of bio-geological research deserves further investigation.

The physical evidence of this large-scale glaciation appears in a number of locations, most notably the sizable gap in the Mountains of the Moon, southeast of The Twins.  Only large-scale glaciation could provide the erosive power necessary to carve this region relatively flat.  In the north, west-northwest of Winterfell, the northern mountains are more subtly eroded, allowing for pines to grow below the tree line.  While not specifically mentioned in texts or personal accounts, large depressions left by the retreating glaciers are typically found on Earth.  And so we have interpreted two such basins: one extending southeast from Winterfell, and the other extending southeast from the Twins.  Each of these depressions, on the order of 100-1000 mi², would later be filled with younger sediments deposited by rivers flowing from the nearby mountains.  While it is difficult to say with certainty, it is possible that the retreating glacier carved out the God’s Eye Lake, south of Harrenhal (similar to the Great Lakes of North America).  This geologic evidence strongly suggests that forty million years ago, winter appears to have come for the entire planet.