Two hundred fifty million years ago, Earth presented a vastly different appearance from the familiar continents and oceans we know today. This period, marking the boundary between the Permian and Triassic geologic eras, reveals a world shaped by unique geological forces, a distinct climate, and a diverse array of life forms.
The Pangea Supercontinent
Nearly all of Earth’s landmasses were united into a single supercontinent known as Pangea. This landform, meaning “all lands” in Greek, had assembled from earlier continental units like Gondwana, Euramerica, and Siberia. Pangea possessed a distinctive C-shape, with its bulk extending across both northern and southern polar regions.
This vast landmass was surrounded by a single ocean called Panthalassa, with the Paleo-Tethys and later Tethys Oceans nestled within Pangea’s C-shaped curve. Pangea occupied approximately one-third of the Earth’s surface, presenting a unified continental expanse unlike anything seen since.
Earth’s Ancient Climate
Earth’s climate 250 million years ago was characterized by generally warmer conditions and a lack of polar ice. Temperature variations between the equator and the poles were less extreme, contributing to a more homogeneous global climate. The size of Pangea significantly influenced these climatic patterns.
The interior regions of the supercontinent were particularly arid, experiencing desert-like conditions due to their distance from oceanic moisture. This continentality led to extreme temperatures. Atmospheric carbon dioxide levels were significantly higher, ranging from around 400 parts per million (ppm) to 2,500 ppm, contributing to a widespread greenhouse effect.
Life on Land and Sea
Life on Earth during this period exhibited unique forms adapted to the prevailing conditions. On land, the dominant vegetation included ferns, seed ferns, and lycophytes in wetter areas, while early coniferophytes, precursors to modern conifers, became increasingly adapted to drier environments. These plant communities supported a diverse range of terrestrial animals.
Among the prominent land animals were synapsids, often referred to as “mammal-like reptiles,” which were the largest terrestrial vertebrates of the time. Early synapsids included pelycosaurs like Dimetrodon, while later forms such as therapsids became more widespread. Early reptiles, including protorosaurs, captorhinomorphs, and the ancestors of archosaurs (which would later give rise to dinosaurs), also diversified during this period. Marine environments were teeming with life, although many invertebrate groups had already experienced reductions in diversity.
The Great Dying and Its Aftermath
Around this time, Earth experienced its most severe known extinction event, often referred to as “The Great Dying.” This event, marking the Permian-Triassic boundary, led to the disappearance of an estimated 81% of marine species and 70% of terrestrial vertebrate species. Even insects, which typically survive mass extinctions, suffered significant losses.
Scientific consensus points to volcanic activity, particularly the eruption of the Siberian Traps, as the primary cause. These eruptions released vast quantities of carbon dioxide and sulfur dioxide into the atmosphere. This influx of gases triggered global warming, ocean acidification, and widespread oxygen depletion in marine environments. The aftermath left an altered planet, paving the way for the rise of new groups of organisms, including the dinosaurs, in the subsequent Triassic period.