Chapter 28, Problem 17STP

Summary Introduction

To explain:

The way the first photosynthetic prokaryotes changed life on Earth.

Introduction:

Scientists speculated that they were the first prokaryotes. The prokaryotic cells are significantly smaller than eukaryotic cells and lack an established nucleus and most other organelles. Many scientists believe that the current prokaryotes are the closest relatives of the first cells on Earth. Often those organisms live in extreme environments.

Explanation of Solution

The photosynthesizing prokaryotes are autotrophic but their energy is not obtained from the Sun. They instead extract energy from inorganic compounds such as sulphur. Archaea does not need to or produce oxygen, either. Scientists believe that, until about 1.8 billion years ago, oxygen was absent from Earth's earliest atmosphere. Any oxygen that appeared earlier than 1.8 billion years ago probably bonded with iron free ions as oxygen does nowadays. Evidence that early-life iron oxide was formed by oxygen is found in unique sedimentary rock formations which are between about 1.8 billion and 2.5 billion years old. Scientists hypothesized that the free iron of early Earth was saturated with oxygen after 1.8 billion years ago, and that oxygen instead started to accumulate in the atmosphere.

Conclusion

Thus, the photosynthesizing prokaryote changed the atmosphere on Earth and makes the planet to live worthy.