Question

Describe two ways in which the sudden appearance of oxygen in the atmosphere about 2.5 billion years ago influenced the development of modern life-forms.

Short answer

Increased oxygen enabled efficient aerobic respiration and led to the formation of the protective ozone layer.

Step-by-step solution

Introduction to the Great Oxygenation Event

Approximately 2.5 billion years ago, the Earth's atmosphere experienced a significant increase in oxygen levels, known as the Great Oxygenation Event. This was primarily due to the photosynthetic activities of microorganisms called cyanobacteria.

Oxygen and Aerobic Respiration

The presence of oxygen in the atmosphere allowed for the development of aerobic respiration. This process is more efficient than anaerobic respiration, providing up to 36 ATP molecules per glucose molecule compared to just 2 ATP from anaerobic processes. This efficiency in energy production led to the evolution of complex multicellular organisms.

Formation of the Ozone Layer

Increased oxygen in the atmosphere contributed to the formation of the ozone layer (O3) in the stratosphere. The ozone layer acts as a shield, absorbing harmful ultraviolet radiation from the sun. This protection allowed organisms to survive and later to thrive in terrestrial environments, facilitating the colonization of land by life-forms.

Key concepts

Aerobic Respiration

The advent of aerobic respiration marked a significant evolutionary milestone. Approximately 2.5 billion years ago, oxygen levels in the atmosphere increased, radically changing biological processes. At this time, organisms began using oxygen for respiration, which led to aerobic respiration.
Compared to anaerobic respiration, where only 2 ATP molecules are produced per glucose molecule, aerobic respiration is incredibly efficient. It can produce up to 36 ATP molecules from the same amount of glucose.
This efficient energy production enabled organisms to develop greater complexity. As a result, multicellular life forms evolved, leading to biodiversity. Aerobic respiration supported more complex organs and systems, providing insights into the evolution of creatures that could sustain more active and energetic lifestyles.

Cyanobacteria

Cyanobacteria, often regarded as some of the most pivotal life forms in Earth's history, played a critical role in the Great Oxygenation Event. These microorganisms, through their photosynthetic activities, were responsible for converting sunlight into energy, while releasing oxygen as a byproduct.
Their emergence and proliferation led to a dramatic accumulation of oxygen in the atmosphere, transitioning it from an anoxic to an oxic state. - Cyanobacteria were the first organisms to produce oxygen through photosynthesis. - Their activity converted what was once a hostile, reducing atmosphere into one more hospitable for diverse life forms. - This shift paved the way for the evolution of aerobic organisms that could exploit the new oxygen-rich environment. Thanks to cyanobacteria, the foundations were laid for the vast and complex webs of life that dominate Earth today.

Ozone Layer Formation

With the increase in atmospheric oxygen, another crucial development took place: the formation of the ozone layer.
Ozone (\(\text{O}_3\)) in the Earth's stratosphere acts as a protective shield, absorbing most of the harmful ultraviolet radiation (UV) from the Sun.
Before the ozone layer, intense UV radiation made the surface uninhabitable for many life forms. The protection the ozone layer provides allowed life forms to colonize land, offering a wider variety of environments to explore and exploit. - The formation of the ozone layer reduced the threat of genetic damage caused by UV radiation.- This allowed evolution to proceed with fewer dangerous mutations, promoting the diversity of species.- As the ozone layer stabilized, ecosystems could expand from the oceans onto land, with plants and animals adapting to terrestrial life.The ozone layer, therefore, played a pivotal role in the extension of life from marine to land habitats.