The Carnian Age, a subdivision of the Late Triassic Epoch, spanned approximately 237 to 227.3 million years ago. This ten-million-year interval represents a profoundly transformative chapter in Earth’s deep history. It was a time marked by significant environmental shifts and widespread biological restructuring that fundamentally reshaped the trajectory of life on our planet.
The World During the Carnian Age
During the Carnian Age, Earth’s geography looked vastly different from today, with most of the planet’s landmass fused into a single supercontinent known as Pangea. This immense landmass was surrounded by a colossal global ocean, the Panthalassic Ocean, with a vast embayment, the Tethys Sea, extending into its eastern tropical latitudes. The prevailing climate across Pangea was generally hot and arid, characterized by expansive deserts in the continental interior. Despite the dryness, this period was punctuated by intense seasonal monsoons, often referred to as “mega-monsoons,” driven by the extreme land-sea distribution.
The Carnian Pluvial Episode
The Carnian Pluvial Episode (CPE), a distinct climatic interval, occurred during the latter part of the Carnian Age, lasting for an estimated 1 to 2 million years, approximately 234 to 232 million years ago. This episode was characterized by a dramatic shift to humid conditions and prolonged, heavy rainfall across much of the globe. Geological evidence, such as siliciclastic sediment layers found worldwide, indicates a significant increase in continental weathering and runoff.
The leading scientific theory attributes the CPE to massive volcanic eruptions from the Wrangellia Large Igneous Province. This vast volcanic region, now located in parts of western North America (Alaska and British Columbia), released enormous volumes of volcanic basalt and gases into the atmosphere. These eruptions peaked during the Carnian, injecting substantial amounts of greenhouse gases, particularly carbon dioxide.
The influx of carbon dioxide triggered a significant greenhouse effect, leading to global warming and an intensified water cycle. This hydrological cycle resulted in widespread and persistent rainfall, drastically altering the previously arid conditions across Pangea. Chemical changes in Carnian strata, including carbon isotope excursions, further support global warming during the CPE.
Life Before and After the Event
Before the Carnian Pluvial Episode, terrestrial ecosystems were populated by a diverse array of life forms. Dominant groups included temnospondyl amphibians, various archosauromorphs (phytosaurs, rhynchosaurs, aetosaurs, and rauisuchians), and synapsids like dicynodonts. Early dinosaurs existed but were generally small, less abundant, and formed a minor component of the overall faunas, typically representing less than 5% of specimens.
The environmental changes during the Carnian Pluvial Episode led to a significant biological turnover, impacting both marine and terrestrial ecosystems. In the oceans, approximately one-third of all marine genera disappeared, including many ammonoids, bryozoa, and crinoids, due to factors like ocean acidification and reduced oxygen levels. On land, prolonged rainfall and climate shifts caused widespread transformations, leading to the decline and extinction of previously dominant plant and herbivore species, such as rhynchosaurs and dicynodonts.
The extinction of these established groups created vacant ecological niches, allowing for the diversification of new life forms after the CPE. This period saw the significant diversification of dinosaurs, which transitioned from a minor group to dominant components of terrestrial ecosystems. Other modern groups also experienced a rise, including conifers and modern reef-building corals, which saw their first appearance and diversification. The reestablishment of large inland lakes and peat swamps also marked the end of an earlier “coal gap.”
The Enduring Legacy of the Carnian
The Carnian Age, particularly the Carnian Pluvial Episode, represents a turning point in Earth’s history. This period of environmental upheaval acted as a catalyst for widespread evolutionary change. The climate shifts and associated extinctions cleared the ecological landscape.
This “reset” allowed for the diversification and rise of dinosaurs, transforming them from minor creatures into the dominant terrestrial vertebrates of the Mesozoic Era. The Carnian also witnessed the emergence and expansion of other modern animal groups, including early mammals, lizards, turtles, and crocodilians, alongside conifer forests. Understanding the Carnian helps us comprehend how life on Earth adapts and recovers from planetary crises, shaping the ecosystems that continue to influence our world.