Final answer:
The earliest living things were simple single-celled organisms. These included domains Bacteria and Archaea, with Archaea potentially originating earlier, around 4 billion years ago. Simple prokaryotic cells like these led to the evolution of more complex forms of life and processes like photosynthesis.
Step-by-step explanation:
The earliest living things on Earth, such as ancient bacteria, were simple in their structure compared to most organisms today. These initial life forms, existing around 4 billion years ago, were single-celled organisms, which are considered the least complex form of life on Earth. Notably, among the first life forms were the domains of Bacteria and Archaea, with Archaea consisting of microbes that thrive in extreme conditions like high temperatures and high salinity. Over billions of years, simple primitive cells eventually gave rise to more complex cells and introduced significant processes such as photosynthesis, which were crucial for the accumulation of oxygen in the atmosphere. The earliest cells were akin to simpler prokaryotic cells, likely composed of a non-phospholipid bilayer membrane and rudimentary RNA.
Cyanobacteria, one of the oldest life forms, played a pivotal role in Earth's history. These were among the first photosynthetic prokaryotes, leading to the creation of oxygen in the atmosphere and contributing to the eventual development of more complex life forms.