Summary
Highlights
55 million years ago, after the extinction of dinosaurs, mammals inherited a restless Earth. Scientists discovered strange formations off Greenland, dating back to this period, suggesting a massive release of methane from the seafloor. This event led to significant global warming, transforming the planet once again.
The warming period, lasting about 5 million years, transformed the planet. In Oregon, evidence of the first angiosperms (broad-leafed flowering trees) like the Katsura tree, dating back 44 million years, suggests that global warming allowed these trees to grow larger, creating an ideal environment for primates to evolve and thrive in their branches.
Living in tall trees necessitated good eyesight for primates. Early primates like Carpolestes, living in shorter trees, evolved to have forward-facing eyes, as seen in species like Shoshonius. The developing broadleaf forests also led to the evolution of a critical feature: the postorbital septum. This bone behind the eye sockets stabilizes the eyeball, allowing for sharper vision (via the fovea) essential for navigating and surviving in the arboreal environment.
The expansion of broadleaf forests and early primates was short-lived. Antarctica's isolation due to continental drift caused the formation of a circumpolar current, leading to global cooling. As temperatures plummeted, broadleaf forests retreated, leaving primates stranded in dwindling forest patches. This cooling drastically changed environments, as evidenced by fossil remains in the Sahara Desert.
Beyond sharp vision, primates developed trichromatic color vision, allowing them to differentiate ripe fruits and fresh leaves, a crucial advantage as food became scarcer. This enhanced eyesight also facilitated the development of complex social bonds. Primates like chimps could recognize subtle facial expressions, allowing them to read emotions and strengthen social structures, a significant step towards human evolution.
Africa is considered the cradle of humanity, profoundly shaped by climate change. The collision of India with Asia formed the Himalayas, which in turn altered atmospheric circulation, leading to distinct seasons in Africa and the expansion of the Sahara Desert. As forests gave way to grasslands, early humans faced extinction, forcing them to adapt their lifestyle.
Evidence from the "Cradle of Humankind" in South Africa reveals that 2 million years ago, two hominid species, Paranthropus robustus and early Homo, coexisted. During a period of global cooling and drying, these species took different evolutionary paths based on their diets. Robustus focused on tough plant foods like tubers, evidenced by their large molars and jaw muscles. In contrast, early Homo chose to eat meat, as shown by cut marks on fossil bones, marking a significant divergence in human evolution.