\(\mathbf{T} / \mathbf{F}:\) Life is responsible for the presence of oxygen in Earth's atmosphere.

Photosynthesis is a fundamental process that occurs in many plants, algae, and some bacteria. This process allows these organisms to convert light energy into chemical energy in the form of glucose. Photosynthesis primarily takes place in the chloroplasts of plant cells using chlorophyll, the green pigment that captures light.

The general equation for photosynthesis can be written as:

\[6CO_2 + 6H_2O + light \rightarrow C_6H_{12}O_6 + 6O_2\]

This equation shows how carbon dioxide and water are transformed into glucose and oxygen through the energy provided by sunlight. The oxygen produced during this process is released into the atmosphere as a byproduct.
The continuous input of oxygen into the Earth's atmosphere by photosynthetic organisms is crucial because it maintains the balance of oxygen needed for many life forms to thrive.

Cyanobacteria, often known as blue-green algae, are some of the oldest and most significant photosynthetic organisms on Earth. These microorganisms have been present on Earth for over 3.5 billion years, contributing significantly to the development of the Earth's atmosphere.

Before cyanobacteria began to proliferate, the Earth's atmosphere had very little to no oxygen. Cyanobacteria were among the first organisms to perform oxygenic photosynthesis, a process that generates oxygen as a byproduct. They utilize sunlight, water, and carbon dioxide to produce glucose and release oxygen.

Over millions of years, cyanobacteria's photosynthetic activity gradually increased the oxygen concentration in the atmosphere, leading to what is known as the Great Oxidation Event (GOE). This event marked a profound change where oxygen became a major component of the Earth's atmosphere, allowing for the evolution of more complex aerobic organisms.

The development of Earth’s atmosphere into its current oxygen-rich state is a complex process that took billions of years. Initially, the atmosphere was composed mainly of volcanic gases such as methane and ammonia, with minimal oxygen.

The transformation began with the emergence of early photosynthetic organisms like cyanobacteria. Through photosynthesis, these organisms released significant amounts of oxygen as a byproduct. This gradual accumulation of oxygen marked the Great Oxidation Event, approximately 2.4 billion years ago.

As oxygen levels increased, it led to significant changes in the atmosphere and oceans. Oxygen not only supported the development of aerobic (oxygen-using) life but also contributed to the formation of the ozone layer, which protects the Earth from harmful ultraviolet radiation. These changes created an environment conducive to the evolution of diverse and complex life forms.

Therefore, life, particularly photosynthetic life, played a pivotal role in transforming the Earth's atmosphere, making it hospitable for a wide range of organisms that rely on oxygen for survival.