GLOBAL CHANGE

Global Change

Global Change

Introduction

Global change is a topic of much debate in recent years, but it is important to realize that Earth's environments have been in a constant state of flux since the formation of the planet, more than four billion years ago. Environmental change has been a main driving force in shaping life on this planet. There have been many causes of environmental change through the uncounted millennia of Earth history; most of the agents of change continue unabated to the present time and most likely will persist long into the future. At the root of nearly all significant environmental change is Earth's relationship to the sun. Other than geothermal energy that escapes from the fiery depths beneath the surface of the earth, the sun is the only source of energy for our planet. This is an important concept to keep in mind when one is considering global change. The sun has affected terrestrial environments on all time scales, from today's weather to the uncharted depths of geologic time. Let us consider the sun's role in global change over these varying time scales, moving from longest to shortest lengths of time. This paper discusses Global Change and its effects and reasons.

Discussion

When the Earth was a newly formed planet, its atmosphere was quite unlike that which blankets the planet today. Before the evolution of plant life, there was far less oxygen in the atmosphere. Plants take in carbon dioxide and give off oxygen in photosynthesis. The relatively thin atmosphere of the primordial Earth allowed far more of the sun's ultraviolet radiation to reach the surface of the planet. This radiation is generally harmful to plant and animal life because it damages cells. The ocean waters that covered much of the planet in Precambrian times were the cradle of life, and one of the reasons for this is that water screens out ultraviolet radiation within a few feet of the surface, so one-celled organisms living in Earth's primordial seas were protected from this dangerous radiation. As the seas began to teem with plant and animal life, the exchange of gases between these organisms and the atmosphere (by way of gases dissolved in sea water) began to change the composition of the atmosphere, which in turn led to an increased atmospheric capacity to screen out ultraviolet radiation. (Allenby, 2009)

Geologists believe that oxygen and carbon dioxide in Earth's atmosphere reached levels roughly equivalent to those of modern times by about 700 million years ago. Another critical component of the atmosphere (past and present) is ozone. Ozone is a molecule composed of three atoms of oxygen that forms in the upper atmosphere. As levels of plant-derived oxygen increased in ancient Earth's atmosphere, the ozone layer in the upper atmosphere began to form. This layer effectively screens out much of the ultraviolet radiation coming from the sun. The energy required to form ozone molecules from free oxygen atoms comes from ultraviolet radiation. (Miller, 2001)

The ozone layer in the atmosphere entered in the news ...