Final answer:
The Earth, about 4.6 billion years old, originally had a molten surface which cooled to solidify and form the atmosphere and oceans. Single-celled prokaryotes were the earliest forms of life, arising around 3.5 to 4 billion years ago. Cyanobacteria played a significant role in transforming the atmosphere, leading to an oxygen-rich environment capable of supporting diverse life.
Step-by-step explanation:
The Earth is estimated to be approximately 4.6 billion years old, a timespan that has allowed for significant geological and biological evolution. Originally in a molten state, the Earth gradually cooled, leading to the solidification of its surface and the formation of the atmosphere and oceans—critical steps for the development of life. Early Earth was characterized by extreme conditions, such as a lack of oxygen in the atmosphere, high levels of radiation, and frequent volcanic activity. Over time, life began to emerge, with the simplest forms appearing around 3.5 to 4 billion years ago. These first organisms were single-celled prokaryotes which eventually gave rise to more complex forms of life.
The first evidence of life on Earth includes the presence of prokaryotes and the development of photosynthetic processes, which would later be responsible for the accumulation of oxygen in the atmosphere. Notably, one of the earliest forms of life that contributed to this change was cyanobacteria, which were responsible for creating the Earth's oxygen-rich atmosphere. This transformation enabled the planet to support the diverse array of life that followed, leading up to the present day.
The theory of the 'primordial soup' suggests that life began in a watery environment where organic compounds were synthesized, providing the building blocks of life. While this theory is still being explored, it aligns with the understanding that early life was likely to have been simple in nature and well-adapted to the harsh conditions of the primitive Earth.