Final answer:
In the Precambrian Era, the presence of stromatolites—fossilized colonies of blue-green bacteria—marks one of the earliest forms of life. Essential evolutionary developments like multicellularity occurred, culminating in a mass extinction that preceded the Cambrian explosion.
Step-by-step explanation:
The Precambrian Era is characterized by the presence of stromatolites, which are fossilized colonies of microorganisms, particularly blue-green bacteria that can photosynthesize. These ancient life forms created layered, domelike structures in shallow waters and are some of the earliest evidences of life on Earth, dating back more than 3 billion years. The late Precambrian, ranging from about 2 billion to half a billion years ago, was a time of significant geologic and climatic changes, leading to the development of multicellularity and a mass extinction event that concluded the era and paved the way for the Cambrian explosion of diverse life forms.
Distinguishing traces of life from the Precambrian can be inferred from the fossil record, with stromatolites being one of the most prominent examples found in ancient sedimentary rock formations. This period also leads up to the emergence of early animal life and evolutionary milestones, like the development of multicellularity. The conclusion of the Precambrian with a mass extinction event led to the Cambrian explosion, which witnessed an unprecedented rise in the complexity and diversity of life.