In the Paleozoic, the paucity of suitable stratigraphic and proxy data presents a formidable challenge. Environmental and climatic proxies—already difficult to interpret due to the stark differences between ancient and later faunal assemblages—must be approached with a degree of skepticism. Compounding this issue is the near-total absence of preserved Paleozoic seafloor. Instead, occasional windows into the nature of Paleozoic oceanic crust are provided by obducted ophiolites (fragments of oceanic crust that thrust onto continents rather than being lost to the mantle via subduction), the rest has long since been subsumed into the mantle. This eliminates key constraints such as the mean age of the oceanic crust, or rates of seafloor accretion and subduction, to guide us in making our reconstructions.