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

Oxygen enabled aerobic respiration and formed the protective ozone layer.

Step-by-step solution

Oxygen and Aerobic Respiration

The sudden appearance of oxygen in the atmosphere enabled the development of aerobic respiration. Previously, life forms relied heavily on anaerobic processes, which are less efficient. Aerobic respiration allowed organisms to extract more energy from the same amount of nutrients, leading to more complex and energy-dependent life forms.

Formation of the Ozone Layer

Oxygen in the atmosphere led to the formation of the ozone layer, which blocked harmful ultraviolet (UV) radiation from reaching the Earth's surface. This allowed life forms to thrive at various depths in the ocean and on land without the threat of radiation damage, paving the way for more diverse and complex ecosystems.

Key concepts

Aerobic Respiration

The presence of oxygen in the Earth's atmosphere marked a major milestone in biological evolution. Prior to this event, many organisms relied on anaerobic respiration, meaning they obtained energy without oxygen. Anaerobic processes are not very efficient, as they extract energy from nutrients, but with much less yield.
With the introduction of oxygen, a new process called aerobic respiration became possible. Aerobic respiration uses oxygen to generate significantly more energy than its anaerobic counterpart. It works by breaking down glucose or other nutrients in the presence of oxygen, producing water and carbon dioxide. This process is much more efficient and allowed organisms to harness much more energy from the same amount of food.

• Higher energy yields from aerobic respiration enabled the development of more complex cellular structures.
• This, in turn, paved the way for multicellular life forms, as more energy resources could support more complex body plans.

By harnessing the power of aerobic respiration, life on Earth shifted towards new levels of complexity, enabling the rich biodiversity we see today.

Ozone Layer Formation

The buildup of oxygen in the atmosphere had another profound impact: the formation of the ozone layer. Oxygen in the atmosphere can undergo chemical reactions under the influence of UV radiation, forming ozone ( O₃ ). The ozone layer became Earth's shield in the stratosphere, playing a critical role in protecting life on our planet. Without the ozone layer, harmful ultraviolet (UV) radiation from the sun would reach the surface in much higher intensities.

• UV radiation can damage genetic material, leading to mutations, cell damage, and even death.
• The ozone layer acts like a blanket that absorbs and blocks a significant portion of this UV radiation.

With the reduction in harmful radiation, life forms were able to thrive both in water and on land. This protective layer was thus essential for allowing life to flourish in diverse environments, leading to complex ecosystems.

Evolution of Complex Life

The Great Oxygenation Event, stemming from increased oxygen levels, triggered dramatic evolutionary changes. The capacity for efficient energy production through aerobic respiration directly influenced the evolution of complex life. Early single-celled organisms eventually gave rise to multicellular organisms. As life forms became more complex, they began to exhibit specialized cells and tissues, adapting to various environments and ecological niches. Higher energy yields also facilitated increased interaction between different life forms, leading to symbiotic relationships, predator-prey dynamics, and more.

• This period laid the groundwork for the evolution of animals, plants, fungi, and other complex organisms.
• Greater energy availability supported brain development, enabling cognitive abilities and advanced behaviors.

Ultimately, the oxygenation of Earth's atmosphere set into motion the evolutionary changes that would culminate in the rich tapestry of life we witness today, including the eventual rise of humans and countless other complex species.