An atom of phosphorus "X" had marked time in the limestone ledge since the Paleozoic seas covered the land. Time, to an atom locked in a rock, does not pass. The break came when a bur-oak root nosed down a crack and began prying and sucking. In the flash of a century the rock decayed, and X was pulled out and up into the world of living things. He helped build a flower, which became an acorn, which fattened a deer, which fed an Indian all in a single year.
—Aldo Leopold, A Sand County Almanac
In this account, Leopold, a pioneer wildlife manager and promoter of environmental stewardship, vividly portrays the flow of atoms between the physical and biological environment and among different organisms. A few of Earth's atoms have changed by radioactive decay, a few have escaped to space, and meteors and meteorites have delivered a few new atoms to Earth. Nevertheless, virtually all of the atoms in our own bodies, and in all other living organisms, have been present on Earth since its formation about 4.5 billion years ago, cycling among its various components.
We began Part One of this book with an introduction to the non-living atoms and molecules that are the building blocks of Earth and of the life found here. It is perhaps fitting that the final chapter should return to these atoms, including them now as part of a larger story. For scientists trained to read them, the atmosphere, rocks, soil, and living organisms harbor clues that tell us about their histories, what was happening on Earth when they were formed, and how they were subsequently transformed. Knowledge of Earth's history helps us understand the changes taking place on Earth today.
Earth system science has emerged as a new field of inquiry that focuses on Earth as a whole. A system is a group of entities that interact to yield some product. For example, an individual animal is made up of systems of organs that work together to perform some function, such as digestion. Earth's system is composed of cycles of materials, inputs of solar energy, and interactions between living organisms and the physical environment. Interactions among these components determine how Earth as a planet functions.
"Time, to an Atom Locked in a Rock, Does Not Pass." The "pillar peaks"of Zhangjiajie National Forest Park in China's Hunan province stand like sentinels in the mist.The atoms in these rocks move through biogeochemical cycles as inorganic atoms from the rock-based soil are taken up by plants.
In this chapter we will describe the major cycles of materials among the compartments of Earth's system. We will show how life has modified Earth's features throughout evolutionary history. We will also show how human alterations of the great biogeochemical cycles continue to modify Earth's system today.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.