Biology 101 : Biology 101 Origin of Life
Origin of Life : Origin of Life The sequence of events leading to evolution of life on earth: The first living things to appear were the simplest creatures, one-celled organisms. From these came more complex, multicellular organisms. More complexity meant more than just an increase in cell number. With more cells came cellular specialization, where certain cells within the multi-cellular organism carried out specific tasks.
Origin of Life : Origin of Life Billions of years of organismal changes have led to the living things we now call plants and animals. Scientists generally concur that the time from the formation of our solar system until now has been on the order of some 4.5 billion years. Those who believe the world as we know it was created in six days are often called creationists . Scientists utilize the scientific method , which allows them to test hypotheses and theories and to develop concepts and ideas.
Origin of Life : Origin of Life Spontaneous Generation Early hypothesis concerning the origin of living organisms from nonliving material is known as spontaneous generation . Aristotle believed insects and frogs were generated from moist soil. 1668, Francesco Redi, an Italian, challenged the concept of spontaneous generation when he tested the widespread belief that maggots were generated from rotting meat. He placed dead animals in a series of jars, some of which were covered with a fine muslin that kept flies out while allowing air in. Other jars containing dead animals were left open. Maggots appeared only on the meat in the jars that were left open. flies had been able to lay their eggs, which then hatched into fly larvae, or maggots.
Origin of Life : Origin of Life Spontaneous Generation During the nineteenth century, following other experiments, the theory of spontaneous generation of microorganisms was laid to rest by experiments conducted in France by Louis Pasteur and in England by John Tyndall. They demonstrated that bacteria are present in the air, and if the air surrounding a heat-sterilized nutrient broth is bacteria-free, then the broth remains bacteria-free. Vitalist doctrine: Adherents of this idea maintained that life processes were not determined solely by the laws of the physical universe, but also partly by some vital force, or vital principle. By the late 1870s, most scientists agreed that all organisms arose from the reproduction of preexisting organisms, and the concept of spontaneous generation had become history.
Origin of Life : Origin of Life Conditions for the Origin of Life Life is thought to have developed through a sequence of chemical reactions over time. Hydrogen, oxygen, and carbon—important components for all life. The present atmospheric gases are composed primarily of molecular nitrogen (N2, 78 percent) and molecular oxygen (O2, 21 percent), with a small amount of carbon dioxide (CO2, 0.033 percent) and many other gases, such as helium and neon, found in only trace amounts. At that time, the atmosphere contained far more hydrogen, and unlike now, there was very little oxygen. In such an atmosphere, the nitrogen probably combined with hydrogen, forming ammonia (NH3); the oxygen was probably found combined with hydrogen in the form of water vapor (H2O), and the carbon occurred primarily as methane (CH4). Long before there was any life on earth, the seas contained large amounts of the simple organic compound methane. Most of the compounds necessary for the development of the initial stages of life are thought to have existed in these early seas.
Origin of Life : Origin of Life Probing Space for Clues of Life’s Origins on Earth Some have concluded that the universe is awash with the chemical precursors of life. From fossil evidence, that bacteria appeared on earth about 3.5 billion years ago, a little more than 1 billion years after the solar system formed. The great challenge has been to learn how, within that first billion years, simple organic chemicals evolved into more complex ones, then into proteins, genetic material, and living, reproducing cells. It is felt that some 4 billion years ago, following the formation of the solar system, vast quantities of elements essential to life, including such complex organic molecules as amino acids, were showered onto earth and other planets by comets, meteorites, and interstellar dust.