Summary
Highlights
The Cenozoic Era, spanning from 66 million years ago to the present, is the third and final era of the Phanerozoic Eon. It is known as the "Age of Mammals" due to their rapid radiation following the end-Cretaceous mass extinction that eradicated dinosaurs. Early mammals were small, with the first primate, Altiatlasius, evolving about 57 million years ago in North Africa. The human genus, Homo, emerged around 2.4 million years ago from Australopithecus, and Homo sapiens appeared between 200,000 and 300,000 years ago in Africa.
During the Cenozoic Era, most continents were already near their current locations, with India's collision with Asia around 50 million years ago initiating the uplift of the Himalayan Mountains. Smaller geographical changes significantly impacted the Cenozoic climate. For instance, Antarctica became isolated about 34 million years ago, leading to a cold ocean current and the development of the first permanent Antarctic ice sheet, marking the beginning of the modern ice age. This global cooling facilitated the storage of atmospheric CO2 in ocean sediments, reducing greenhouse warming.
Glaciers developed in the Northern Hemisphere around 3.2 million years ago, likely due to the closing of the Isthmus of Panama. This event reorganized ocean circulation, making the Atlantic much saltier and altering the Gulf Stream, which led to cooling and ice sheet development in regions like Greenland and Northern Europe. Earth has been in this Northern Hemisphere ice age since. Within an ice age, glacial and interglacial periods occur, primarily influenced by Milankovitch Cycles—changes in Earth’s orbit including precession, obliquity, and eccentricity, which operate on timescales of tens to hundreds of thousands of years.
Currently, Earth is in an interglacial period. However, despite what Milankovitch Cycles suggest, the planet is heading towards a subtropically warm Arctic without ice sheets, largely due to global warming caused by the burning of fossil fuels. This discussion concludes the series on the history of Earth's timeline, setting the stage for future explorations of geological structures.