Introduction

Welcome to 7.12, Origins of Life on Earth, the last topic of unit 7 of AP Biology. After this topic, we are in the homestretch as only one unit remains. Topic 7.12 is purely theoretical and under no circumstances is meant to clash with religion. At the end of this article, you should be able to describe the origins of life on earth and explain the RNA World Hypothesis.

Origins of Life

There is important scientific evidence to support the origin of life on earth. One such piece of evidence is geological evidence. Geological evidence reinforces models of the origin of life on Earth. Earth was formed approximately 4.6 billion years ago (BYA). In other words, Earth was around for 700 million years before any life appeared. However, Early earth was not suitable for life due to the hostile environment on Earth at that time. The Early Earth became suitable for life around 3.9 BYA. Taken together, this evidence provides a plausible range of dates for the origin of life. The earliest fossil is estimated to be from 3.5 BYA (cyanobacteria).

How did Life Arise?

Early Earth contained inorganic molecules (referred to as the primordial soup). These could have been synthesized into organic molecules due to the availability of free energy and abundant oxygen. Organic molecules could have also been transported to Earth via meteorites or other celestial events.

Experimental Data

Alexander Oparin and John Haldane hypothesized that early Earth was primarily composed of hydrogen, methane, ammonia, and water. This became known as the Oparin-Haldane Hypothesis. Stanley Miller and Harold Urey tested the hypothesis in their laboratory and found that organic compounds and amino acids formed. Miller and Urey hypothesized that the organic molecules that formed served as the building blocks for macromolecules.

The RNA World Hypothesis

The RNA World Hypothesis proposes that RNA could have been the earliest genetic material. The three assumptions are:

Conclusion

Ultimately, scientists have studied how life arose for decades or even centuries. While there’s no central agreement, experimental data has led to the formation of several theories, including the RNA World Hypothesis.

Practice Questions