Threads Of Life :: essays research papers

Thread of Life   Ã‚  Ã‚  Ã‚  Ã‚  This book covers the patterns of evolution and how each species and time era had an effect on Earth’s history. It covers the world from the beginning to the present times telling us all that has happened in between.   Ã‚  Ã‚  Ã‚  Ã‚  The book begins by introducing us to geology and how it is used in telling time and finding fossils. The Grand Canyon is a good place to begin because it is the worlds greatest geological gash. Sediment was deposited here layer upon layer and eventually the layers were cut through by the Colorado River. The time covered by the layers of rock in the Grand Canyon represent about two billion years of earths history.   Ã‚  Ã‚  Ã‚  Ã‚  The next chapter introduces to us how life began. Many scientists believe that life began as soon as the earth cooled sufficiently after just forming. It is believed that the first life on earth emerged some four billion years ago. The author goes on to say that the beginning of life can be organized into five stages: first, the earth forms from materials in our solar system; second, chemicals such as sugars, phosphates, and amino acids are formed; third, these building blocks link together to form nucleic acids, proteins, carbohydrates, and fats; fourth, these turn into proto-organisms; and last, these organisms gain the ability to replicate. This explains how life begins.   Ã‚  Ã‚  Ã‚  Ã‚  Soon the organisms of the water begin to evolve legs and lungs and start to venture out of the water onto the land. This brings about the era of the dinosaurs. Dinosaurs ruled the earth for about 185 million years and then their populations began to decline. About 65 million years ago there is evidence that an asteroid struck the earth and caused the extinction of many species of marine plankton. The last of the dying dinosaur population may have died out before this.   Ã‚  Ã‚  Ã‚  Ã‚  After the dinosaurs died off, then came the reign of the mammals. Mammals were more equipped for survival because of more intelligence and the development of a lower jaw comprised of one bone. Upper and lower molars helped mammals survive better. Mammals would also stay with there young and nurture them until they were able to fend for themselves. Mammals were able to survive a very long time and are still evolving in present times.   Ã‚  Ã‚  Ã‚  Ã‚  In the present, there is evidence that our human ancestors walked erect some 3.75 million years ago.