The scandalous wedding of young Robb Stark to Jeyne Westerling isn’t the only thing to have been stained red in the history of Westeros (spoiler!).  The Red Keep, home to the Iron Throne in King’s Landing, appears to be made of red-hued sandstone.  We again assume that the quarry is near King’s Landing to facilitate construction, and that the sand was likely eroded from the aptly named Red Mountains to the south.  The crimson coloration might come from a variety of sources, including ferric iron oxide hematite (an iron mineral) that also binds together the New Red Sandstone found in the UK on Earth.  This mineral is indicative of terrestrial origin, suggesting formation within a desert environment.  From our analysis of the size of the Game of Thrones planet, we know that deserts form within a narrow latitude range near 30°.  And our analysis of the Winterfell Limestone suggests that Winterfell was located near 25° north 300 Mya.  We therefore conclude that the Red Keep Sandstone originated in a terrestrial desert environment on southern Westeros around 450 Mya, when King’s Landing, and the entirety of southern Westeros, was within the southern hemisphere.  This approximate age is constrained by the eons required for tectonic forces to translate southern Westeros to its eventual collision with northern Westeros 350 million years later.

The Red Orogeny is the earliest piece of Westeros’ geologic history that we can infer with the available data.  From our analysis of the Red Keep Sandstone and the Winterfell Limestone, we know that Westeros has moved gradually north throughout its history.  From this, we can infer that the Red Mountains formed as oceanic crust to the south subducted beneath continental crust to the north.  An oceanic spreading ridge (like the mid-Atlantic ridge) located south of the map likely drives this process.  When the Red Mountains formed, they likely extended into southern Essos as the oceanic plate subducted beneath the entire continent.  Due to their age, and perhaps more dominant weathering and erosion on the eastern flank of the range due to climatic conditions, the Red Mountains in Essos have been lost to time.  The Red Mountains are notably lower in elevation and far easier to traverse, betraying their true age.  The morphology of such weathered mountains is similar to the Appalachian Mountains in the eastern US, which formed around 500 Mya.  We infer a similar age for the Red Mountains.

On Earth, nearly all iron ore comes from specific rocks called banded iron formations, the vast majority of which originate around 2,000 million years ago (2,400-1,800 Mya to be more precise).  At this time, the world’s oceans were far more acidic, able to dissolve iron minerals.  The acidity arose due to the large amount of carbon dioxide in the atmosphere that dissolved in the oceans to form carbonic acid.  Around 2,000 million years ago, there was no breathable oxygen on Earth’s surface.  But then, a cellular mutation allowed certain bacteria to breathe in carbon dioxide and breathe out oxygen – the birth of photosynthesis.  The new bacteria thrived.  As they pumped oxygen into the oceans, it bonded with the iron minerals that then precipitated as solid sediments onto the ocean floor.  For reasons still being investigated by earth scientists, the available oxygen fluctuated through time.  When there was an abundance of oxygen, the ocean sediments became rich with iron-oxide minerals.  When there was a dearth of oxygen, the ocean sediments returned to their anoxic, muddy state (forming chert).  This cycle repeated for 100s of millions of years, creating alternating bands of rock, some with precipitated iron, some without: the banded iron formations.  If Westeros has followed a similar geologic evolution as Earth, then the Iron Islands record the birth of breathable air on the Game of Thrones planet.