Standing on the surface of the world today, it is easy to view the landscape as a constant. The continents sit in familiar positions, the oceans fill the basins between them, and the cycle of day and night seems eternal. Yet, if we could rewind the clock 100 million years, to the early Cretaceous period, we would find a planet so alien that it might as well be another world. This was an era when the Earth was a greenhouse world, when the seas rose high to swallow the continents, and when life evolved in ways that challenge our modern imagination.
The Shifting Stage: A World Without Our Maps
To understand what the world looked like 100 million years ago, one must first dismantle the very concept of the map we know today. The continents were not the separate landmasses we recognize; instead, they were fragments of a supercontinent in the process of breaking apart. During the Jurassic, the mighty Pangaea had fragmented into two large landmasses: Laurasia in the north and Gondwana in the south. By 100 million years ago, this breakup was accelerating. The Atlantic Ocean was a narrow, shallow seaway, while India was just beginning its frantic northward rush toward Asia. South America was still connected to Africa, and Australia was locked tight with Antarctica, forming a continuous southern landmass that blocked the circumpolar current.
The Greenhouse World and the Epeiric Seas
The climate of this ancient world was profoundly different from the ice ages and mild cycles we experience today. Carbon dioxide levels were extremely high, pushing global temperatures up by as much as 6 to 8 degrees Celsius above pre-industrial levels. There were no polar ice caps; instead, the planet was a humid, steamy hothouse where crocodiles roamed the high latitudes. This warmth allowed the seas to expand and the continents to be submerged. Vast inland seas, known as epeiric seas, flooded the interiors of the continents. In what is now North America, a massive seaway split the continent in two, creating a chain of shallow seas that teemed with life and deposited the thick layers of chalk and shale that today form the bedrock of regions like Kansas and Nebraska.
The Dominant Life of the Land
On land, the age of the dinosaurs was in full swing, but the ecosystem was in a state of dynamic transition. The great sauropods—long-necked giants like *Argentinosaurus* and *Patagotitan*—were reaching the peak of their dominance, their colossal size a direct response to the abundance of lush vegetation. They were not alone. Theropod dinosaurs, the carnivorous hunters, were evolving into more sophisticated predators. While the massive *Tyrannosaurus rex* was still 40 million years in the future, its ancestors, such as *Acrocanthosaurus*, were the apex predators of their time, stalking the floodplains with terrifying efficiency. Flying reptiles, the pterosaurs, ruled the skies, with species like *Pteranodon* casting shadows over the inland seas, while the first true birds, such as *Confuciusornis*, were beginning to appear, representing an entirely new branch of life taking to the air.
Forests of Ferns and the Rise of the Angiosperms
Walking through the Cretaceous landscape would have felt like entering a primordial jungle. The dominant flora was not the familiar conifers of the past but a new and revolutionary group of plants: the angiosperms, or flowering plants. These plants were rapidly diversifying, evolving vibrant flowers and fruits to attract pollinators and spread their seeds. Their rise reshaped the planet, creating new niches for insects and other animals. Giant ferns and cycads formed the understory, while towering conifers and the first deciduous trees competed for sunlight in the canopy. This botanical revolution was the foundation of the modern forests and grasslands, driving the co-evolution of life that would eventually lead to the ecosystems we see today.
More perspective on What did the world look like 100 million years ago can make the topic easier to follow by connecting earlier points with a few simple takeaways.
