Paleocene

The Paleocene was a major geological epoch in Earth's history. It lasted from approximately 66 to 56 million years ago (Ma). This epoch marks the very beginning of the Paleogene Period. It also sits at the start of the modern Cenozoic Era. The name comes from Ancient Greek words. "Palaios" means old, and "kainos" means new. Together, it translates to "the old part of the Eocene."

This era was a bridge between the age of dinosaurs and the modern world.

The epoch began with a massive catastrophe known as the K–Pg extinction event. This event was likely caused by the Chicxulub impact, where a large asteroid hit the Yucatán Peninsula. Volcanism from the Deccan Traps may have also contributed. This disaster killed about 75% of all species on Earth. Most famously, it ended the reign of the non-avian dinosaurs.

This sudden loss of life caused a massive turnover in species. Many previously common animals vanished. They were replaced by species that were previously uncommon or rare.

During the Paleocene, the Earth's physical environment was very different. The climate was a greenhouse climate. This means the global average temperature was much higher than it is today. There were no permanent ice sheets at the North or South Poles. Because of this warmth, thick forests grew all over the planet. Even the polar regions were covered in lush plant life.

However, these forests had low species richness compared to later times. Most animals were quite small. They were rapidly evolving to fill the empty spaces left by extinct species. While some animals grew large, most remained small and moved through dense forests.

Geography was also in a state of constant change. The continents were not in their current positions. In the Northern Hemisphere, land bridges still connected some continents. South America, Antarctica, and Australia had not yet completely separated.

In the mountains, the Rocky Mountains were undergoing uplift. The Indian Plate had also begun its slow collision with Asia. In the oceans, the circulation of water was different. Instead of the North Atlantic, downwellings likely occurred in the North Pacific. Water density was controlled mostly by salinity rather than temperature.

Geologists divide the Paleocene into three distinct stages. These stages are the Danian, the Selandian, and the Thanetian. The Danian is the first stage, spanning from 66 to 61.6 Ma. It was first defined by Pierre Jean Édouard Desor using Danish chalks. The Selandian follows from 61.6 to 59.2 Ma. It is often studied at the sea cliffs of Zumaia, Spain.

Finally, the Thanetian lasts from 59.2 to 56 Ma. Scientists use specific fossils and magnetic shifts to tell these stages apart. For example, the appearance of the algae *Discoaster* helps mark the Thanetian.

The Paleocene ended with a massive climatic event. This is called the Paleocene–Eocene Thermal Maximum, or PETM. During this time, about 2,500 to 4,500 gigatons of carbon were released. This carbon entered the atmosphere and the ocean systems. The result was a sudden spike in global temperatures. It also caused ocean acidification. This event led to the extinction of 30% to 50% of certain marine species.

These species, called benthic foraminifera, are vital indicators of ocean health.

We can still find the physical remains of the Paleocene today. Many important energy resources formed during this epoch. Large coal deposits were created, such as the Cerrejón mine in Colombia. This is one of the largest open-pit mines in the country.

Other coal is found in Svalbard, Norway, and the Canadian Arctic. In the North Sea, the Paleocene left behind massive reserves of natural gas and oil. These resources total billions of barrels of oil and trillions of cubic meters of gas. The Paleocene was a time of recovery, change, and immense geological power.