Final answer:
The theory that all life on Earth descended from a common ancestor that lived 3.5 billion years ago is the theory of common descent, which is central to evolutionary biology. The three domains of life, Bacteria, Archaea, and Eukarya, all evolved from this common ancestor, with fossil evidence of microbial life dating back to these ancient times.
Step-by-step explanation:
The theory that states that all life on Earth is descended from an original life form that lived 3.5 billion years ago is the theory of common descent. This theory is a fundamental concept in evolutionary biology and posits that all organisms on Earth have descended from a single common ancestor. This ancestral cell emerged soon after the origins of life on our planet. When we consider the domains of life—Bacteria, Archaea, and Eukarya—it's believed that they all evolved from this common ancestral cell. Our understanding of the origin of life also includes the formation of large colonies called stromatolites around 3.5 billion years ago, evidence of which is still present today.
Fossil evidence from 3.5-billion-year-old rocks shows signs of microbial life, and while the detailed sequence of molecules-to-biology is not fully understood, this evidence supports the timeline for when life began to diversify. The three domains of life had evolved by 1.5 billion years ago. This evolutionary process is supported by biochemical similarities and theories such as endosymbiosis, which helps explain the rise of eukaryotic cells.