Final answer:
The fossils described as disks, fronds, or blobs are characteristic of the Ediacaran fauna from the Ediacaran period, which were complex multicellular organisms predating the Cambrian explosion. Option 4 is correct answer.
Step-by-step explanation:
The question asks about which fossils often took the form of disks, fronds, or blobs. Among the options provided, Ediacaran fauna is known for such characteristics.
Fossils from the Ediacaran period (between 543 and 635 million years ago) are notable for their peculiar and diverse forms, including the disk-shaped Cyclomedusa, the frond-like Dickinsonia, and blob-like structures. These multicellular organisms represent some of the earliest complex life forms on Earth.
In contrast, prokaryotes, including bacteria, typically do not form such complex structures as fossils. The Cambrian period, which followed the Ediacaran, is known for the Cambrian explosion, where a vast diversity of life forms emerged, but it is not a type of fossil. Stromatolites are layered bio-chemical accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria. However, they do not typically take the shape of disks, fronds, or blobs as indicated in the question.
Therefore, the correct option is 4) Ediacaran fauna.