Introduction

Abstract

How do you know if something is alive? The answer might seem pretty clear for large creatures, but is not so obvious for single-celled critters. This chapter discusses some of the attempts to define the criteria that determine if something is alive. It also discusses the origin of Earth, the conditions that existed on early Earth, and how those conditions changed so life could eventually survive and flourish. The time-honored Miller–Urey experiment is described; it has been used for decades to describe how some of the molecules of life, specifically the amino acids, might have been produced on early Earth. This chapter then introduces the concept of chirality, or handedness, which is a property of the amino acids, and which raises serious questions about the Miller-Urey based explanation of the origin of life on Earth. Finally, a model is introduced that might explain how the amino acids achieved this chirality, and which allowed them to become the building blocks of more complex molecules of Earthly, and possibly cosmic, life.