The correct answer is D. Palaeocene.
The Palaeocene is the lowermost and oldest epoch of the Tertiary Period of geologic time, lasting from approximately 66 million to 56 million years ago. It follows the Cretaceous Period and is followed by the Eocene Epoch. The Palaeocene is the first epoch of the Paleogene Period.
The Palaeocene was a time of great change on Earth. The dinosaurs had become extinct at the end of the Cretaceous Period, and the mammals were beginning to diversify and fill the ecological niches that had been left vacant. The first primates and horses appeared during the Palaeocene.
The climate of the Palaeocene was warm and humid, with a global average temperature that was about 5 degrees Celsius warmer than today. The Earth’s continents were still largely in their current positions, but there was more land in the Southern Hemisphere than there is today.
The Palaeocene ended with the Paleocene-Eocene Thermal Maximum, a period of rapid global warming that lasted for about 100,000 years. The cause of the Paleocene-Eocene Thermal Maximum is still debated, but it may have been caused by a sudden release of methane from the Earth’s crust.
The Palaeocene is a relatively short epoch, but it was a time of great change on Earth. The dinosaurs had become extinct, and the mammals were beginning to diversify and fill the ecological niches that had been left vacant. The first primates and horses appeared during the Palaeocene, and the climate was warm and humid. The Palaeocene ended with the Paleocene-Eocene Thermal Maximum, a period of rapid global warming.