Eukaryotes are organisms with a nucleus. The oldest evidence of eukaryotes is from 2.7 billion years ago. Scientists believe that a nucleus and other organelles inside a eukaryotic cell formed when one prokaryotic organism engulfed another, which then lived inside and contributed to the functioning of its host.Click to see full answer. Herein, how old are prokaryotic cells?The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the Earth’s crust. Eukaryotes only appear in the fossil record later, and may have formed from endosymbiosis of multiple prokaryote ancestors. what are the 4 types of eukaryotic cells? There are four types of eukaryotes: animals, plants, fungi, and protists. Protists are a group of organisms defined as being eukaryotic but not animals, plants, or fungi; this group includes protozoa, slime molds, and some algae. Secondly, what era did eukaryotes first appear on Earth? Eukaryotes evolved approximately 1.6–2.1 billion years ago, during the Proterozoic eon.What defines a eukaryotic cell?An organism whose cells contain a nucleus surrounded by a membrane and whose DNA is bound together by proteins (histones) into chromosomes. The cells of eukaryotes also contain an endoplasmic reticulum and numerous specialized organelles not present in prokaryotes, especially mitochondria, Golgi bodies, and lysosomes.