The world 250 million years ago was an alien landscape defined by a catastrophic event that reset the planet’s biology and environment. This time marks the beginning of the Mesozoic Era and the Early Triassic Period. It immediately followed the Permian-Triassic extinction event, known as “The Great Dying,” which remains the most severe loss of life in Earth’s history. The devastation was immense, with an estimated 90% of all marine species and 70% of terrestrial vertebrate species vanishing. Earth entered a long period of ecological recovery, as surviving life forms adapted to a radically altered global geography and an extreme, volatile climate.
The Supercontinent Pangaea
At this time, nearly all of Earth’s continental crust was fused into one immense landmass known as Pangaea, meaning “all lands.” This supercontinent stretched from pole to pole, forming a colossal, C-shaped mass that profoundly shaped global geography. A single, vast ocean, Panthalassa, surrounded Pangaea, while the Tethys Ocean formed a large embayment on its eastern side.
The tectonic forces that created this landmass also formed colossal mountain ranges along the suture zones where continents collided. The Central Pangean Mountains, the predecessor to the modern Appalachians, were still relatively young, standing at heights comparable to the modern Himalayas. Formed by the collision of ancient Africa and North America, these mountains ran as a massive backbone through the center of the continent.
Even as Pangaea was fully assembled, the stresses that would eventually tear it apart were already beginning to manifest. Rift valleys started to form in the continental crust, signaling the beginning of the supercontinent’s slow breakup. These early cracks, filled with sediments and volcanic material, would eventually become the seafloor of the Atlantic Ocean. The internal forces of plate tectonics had already started the process of fragmentation.
Extreme Climate and Vast Deserts
The unification of the continents into Pangaea created a unique and extreme global climate system. With no continental barriers to deflect air currents, the single landmass severely restricted the penetration of oceanic moisture into its interior. This resulted in a hyper-arid continental core, dominated by colossal, deep deserts far from any moderating influence of the sea.
The average global temperature was significantly warmer than today, primarily due to high concentrations of atmospheric carbon dioxide. Estimates suggest CO2 levels may have been as high as 2,500 parts per million (ppm), fueling an intense greenhouse effect. This heat, coupled with the lack of ice sheets at either pole, meant that temperature differences between the equator and the poles were much less pronounced than they are today.
Despite the overall aridity, some coastal regions were subject to intense seasonal monsoonal weather patterns. These massive rain systems were driven by the extreme temperature contrast between the hot landmass and the surrounding ocean, bringing seasonal relief to localized areas. The climate remained unstable, with evidence suggesting periods of rapid global temperature fluctuations following the volcanic eruptions of the Siberian Traps.
Life in the Early Mesozoic
The biological appearance of Earth 250 million years ago was one of profound impoverishment and slow recovery. The mass extinction event had decimated plant life, leading to the “coal gap,” a period where virtually no new coal deposits were formed due to the collapse of swamp ecosystems. Terrestrial flora was dominated by hardy, stress-tolerant species, such as conifers, ferns, and gymnosperms, which proliferated in the arid conditions.
The terrestrial fauna was characterized by low diversity and a temporary dominance of generalist survivors. Among the most common vertebrates was the synapsid Lystrosaurus, a sturdy, pig-sized herbivore whose fossils are found across multiple continents, reflecting the unified landmass of Pangaea. This animal’s success suggests an ability to survive on a limited diet and adapt to harsh, unstable environments.
Over time, new groups began to diversify and fill the vacated ecological niches. This recovery period saw the rise of the archosaurs, a group of reptiles that included the ancestors of crocodiles, pterosaurs, and dinosaurs. While the first true dinosaurs would not appear until later in the Triassic, the diversification of archosaurs set the evolutionary stage for the Mesozoic Era’s famous giants. The overall ecological complexity of the planet would take many millions of years to rebuild.