Did you have been to Natural History Museum? I, Jeong Keun went to Museum of Natural History, and I saw about Universe and history of living things. I shall now tell you about four Eras of living things.

 The first Era is Precambrian Era. It was very important because there was cyanobacterias. They made the oxygen by photosynthesis with te sun. The oxygen created living things by making the important things to live. I had interested in 'EXTREMLY' important cyanobacterias. The reason why I thourht like that is two : there should be no people without cyanobacterias, and there was living things which make oxygen such as plants, in Precambrian Era.

 The next Era is Paleozoic Era. In this Era, there was plant making oxygen like cyanobacterias. Representative example of plant is bracken, which is known for good at constipation. Also, there was animals living under the sea as ostracoderms, and trilobite.

 In Mesozoic Era, as well as you know, the dinosaurs lived. You should know that dinosaurs are divided into three parts-carnivores, herbivors, and omnivors. Carnivores, who is meat-eating, has sharp teeth, paws, and chins. The example of carnivores are acrocanthosaurs, sho has saw-like protrusions. Herbivors stands for plant-eating dinosaurs or animals. Stegosaus with small head and round chin is the representative herbivors. Omnivors eats both of them, meat and plant. I hope you'd know what's the well-known, yes, people.

 Cenozoic Era is the most modern in all four of Eras- Precambrian Era, Paleozoic Era, Mesozoic Era, and Cenozoic Era. This Era was time of mammoth at first, but because of the Ice Age with super-cold days, all of mammoth had been killed and it came the time for human.

 To sum up, there are Precambrian Era for oxygen-making cyanobacteria. Second Era, Paleazoic Cra was for vracken, ostracoderms, and trilobite, etc. Next is Mesozoic Era, the era for dinosaurs-carnivores, herbivors, and omnivors. Cenozoic Era is for mammoth until Ice Age, but it became humans'. I learned lots of things by traveling Museum of Natural History, even I want to go again. Thank you for reading my essay, and I hope you it helped you for understanding about four eras!