answers: Cenozoic
context: approximately 542 million years ago. It consists of three eras: The Paleozoic, Mesozoic, and Cenozoic, and is the time when multi-cellular life greatly diversified into almost all the organisms known today. The Paleozoic ("old life") era was the first and longest era of the Phanerozoic eon, lasting from 542 to 251 Ma. During the Paleozoic, many modern groups of life came into existence. Life colonized the land, first plants, then animals. Two major extinctions occurred. The continents formed at the break-up of Pannotia and Rodinia at the end of the Proterozoic slowly moved together again, forming the supercontinent Pangaea in </s> research. Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by plate tectonics, weathering and hydrothermal circulation. All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter nuclide (a species of atom characterised by the number </s> that war's exigencies, such as jet aircraft, rocketry, and electronic computers. In the decades after World War II, these advances led to jet travel, artificial satellites with innumerable applications including global positioning systems (GPS), and the Internet—inventions that have revolutionized the movement of people, ideas, and information. However, not all scientific and technological advances in the second half of the 20th century required an initial military impetus. That period also saw ground-breaking developments such as the discovery of the structure of DNA, the consequent sequencing of the human genome, the worldwide eradication of smallpox, the discovery of plate tectonics, manned
question: which is the first era of earth 's history