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.
Determining the age of the various Westeros mountain ranges is problematic without geochemistry; the wildlings make sample collection difficult. However, we can infer ages based on the current shape, or morphology, of the mountains. As Jon Snow and the men of the Night’s Watch have observed, the northern mountains, which we will call the Black Mountains, are jagged, rocky, snowcapped and quite treacherous to cross. This jagged morphology suggests that the Black Mountains are relatively young, and the morphological similarity to the Rocky Mountains in the western US suggests that the Black Mountains are 60-80 million years old. During this time of mountain building – called orogeny – an oceanic plate began to subduct beneath the northern territories of Westeros. As the plate slid deeper into the planet, the heat of the mantle boiled away the water, which in turn melted the rock above, which then erupted forth as lava at the surface and created the volcanic mountain range (this form of volcanism is common on Earth, and is primarily responsible for the “ring of fire” around the margins of the Pacific plate). Again, we are somewhat troubled by the lack of documented volcanism in the Black Mountains. Our only explanation is that subduction of the plate ceased for some unknown reason, thereby killing the volcanic engine.
The evidence of plate subduction is heavily inferred from geologic features found in Winterfell, specifically the hot springs that keep the town warm during winter, and the protective granite walls that secure the town’s interior. While hot springs have multiple geologic origins, we propose that the Winterfell hot springs are the result of faulting – cracks in the crust that allow water to flow deep within the earth, get heated, then return to the surface via other faults (hot springs of this sort can be found all over the world, including coastal California). The tremendous pressures involved as the plate subducted beneath the northern territories were surely enough to have caused faulting of this type, and the inferred volcanism would provide more than ample heat. Thus, we interpret the Winterfell hot springs as fault-caused, consistent with plate subduction. The protective granite walls offer more evidence of plate subduction. Granite is an intrusive igneous rock, meaning that a magma chamber never erupted and the large body of molten rock cooled to granite within the earth. Intrusive granites are common in subduction zones (think, Sierra Nevada mountains in California). Given Winterfell’s proximity to the Black Mountains, we propose that a granite quarry must be nearby, easing the distance traversed by the giants of legend who hauled the granite slabs to Winterfell.
The rise of the Mountains of the Moon is perhaps the best-documented geologic event on Westeros, and is directly responsible for the tremendous wealth of the House Lannister. Similar to the Black Mountains to the north, the Mountains of the Moon are jagged, rocky, and snow capped. Based on morphology alone, we cannot rule out that the Black Orogeny and the Moon Orogeny occurred simultaneously. However, analysis of the most-likely faulting geometry reveals that the Mountains of the Moon exist to the south of a microplate (yes, microplates exist on Earth too). Based on this geometry, it is more likely that the Moon Orogeny occurred slightly earlier than the Black Orogeny (similar to the microplate tectonics responsible for the Mariana Trench and volcanic island arc of Japan). Knowing that the Black Mountains are 60-80 million years old, we therefore surmise that the Mountains of the Moon are 80-100 million years old, comparable to the Canadian Rocky Mountains in North America. The Moon Orogeny is more complex than the Black Orogeny, and we propose that the Mountains of the Moon formed in two stages: 1) early subduction of the microplate beneath southern Westeros, and 2) later continental collision between northern and southern Westeros.
The more recent continental collision between northern and southern Westeros is evident in the width of the Mountains of the Moon, far wider than the Black Mountains, and nearly twice the width of the Himalaya on Earth. While most mountain ranges on Earth formed as a result of subduction (think: Rocky Mountains, Alps, and Andes), the much larger and wider mountains of the Himalaya formed as a result of two continents (India and Asia) colliding with little to no subduction. This is the most striking evidence of a collision between northern and southern Westeros. Yet these mountains are also home to Casterly Rock and the gold deposits from which the House Lannister has so benefited. Gold is typically deposited on the ocean floor near mid-ocean vents. The gold mixed with the basalt (extrusive igneous rock) until it reached a subduction zone. As the oceanic crust that previously separated northern and southern Westeros subducted beneath the southern part of Westeros, layers of ocean rock were scrapped off (like a bulldozer), accreted onto the continent, and uplifted. The heat and pressure of subduction dissolved the gold, which then intruded into the overlying rock and solidified within quartz veins (this is where the gold from the California Gold Rush came from). The presence of the Lannister gold (and silver found at Silverhill to the south) supports the notion that subduction tectonics played an equally important early role in the Moon Orogeny.
The final piece of evidence that northern and southern Westeros were previously separate continents is the Iron Islands. On Earth, iron ore is most widely extracted from rocks known as banded-iron formations (more on these later). These rocks formed in shallow oceans. During the initial subduction phase, the ocean floor that wasn’t directly scraped off onto southern Westeros (as Casterly Rock had) was uplifted, pushing the banded iron formations that make the Iron Islands to the surface. Millions of years of exposure, erosion, and weathering have left behind only the strongest of rocks. But their very presence owes to uplift caused by the subduction of the microplate.
Long ago, the territory surrounding Winterfell was not prowled by direwolves, but rather by corals, fish, and perhaps the occasional reef shark. While we know that Winterfell’s protective walls are made of granite, the grey hue of the majority of the fortress suggests a different building material, which we interpret as limestone (a common building material during the middle ages on Earth). And limestone, if you have not already surmised, is formed by large “carbonate factories” typically associated with shallow seas and reefs. The evidence for limestone is indirect but compelling, and requires a step back to survey the territory surrounding Winterfell more broadly. To the southwest of Winterfell lie the Flint Cliffs (which we choose to interpret literally). Flint is a form of chert, a siliceous rock that forms on the shallow ocean floor. The proximity of shallow ocean rocks to Winterfell suggests an oceanic origin to the stones used to build the castle. The presence of caves used as crypts by the family Stark suggests karst topography, which is indicative of limestone and the “swiss cheese” geology associated with subsurface water eroding complex cave systems (think, Carlsbad Caverns in New Mexico, USA, or Waitomo Caves in New Zealand). The rapidly flowing subsurface water would also help explain the Green Fork River, originating near The Twins. The rivers that pass through The Twins are somewhat problematic given that the vast majority (~99.9%) of rivers on Earth begin in areas of higher elevation (like mountain ranges). Yet these rivers seem to simply appear, much like the Warlocks. We propose that these rivers originate from complex subsurface water pathways making their way to the surface through the chert and limestone, emerging as springs. Again, while indirect, the combined observations of grey building stones, flint, karst topography, and the Green Fork River strongly suggest that Winterfell sits near large limestone deposits.
Dating the Winterfell limestone is more complicated, but not impossible. Reefs on Earth only appear within a narrow range of latitudes, approximately 30° north to 30° south (at least in the modern climate – during warmer greenhouse conditions, the latitudinal range is much broader). Currently, Winterfell sits at near 60° north, far too cold for coral reefs, even during greenhouse conditions. This suggests that Winterfell, and indeed the entire continent, has moved over the eons, further supporting our early assertion of active tectonics. Earlier, we concluded that the limestone was likely uplifted during the Moon Orogeny, 80-100 Mya. Therefore, we know that the Winterfell limestone is older than 100 million years. More exact dating requires comparison to similar rocks on Earth: the Carboniferous Limestone of Great Britain and Ireland. The Carboniferous Limestone currently sits at similar (within 5°) latitude as Winterfell, and like the Winterfell Limestone, formed as ocean sediments much closer to the equator. The Carboniferous Limestone is approximately 350 million years old, and required an elongate and curvilinear journey to move from the tropics to its current location. We assume a more direct path for the Winterfell Limestone, and therefore place an approximate age of 280-300 million years.