1. what evidence supports the notion that sponges are some of the earliest known multicellular animals?

"Chemical fossils"evidence supports the notion that sponges are some of the earliest known multicellular animals.

Explanation:

Sponges are multicellular animals, may belong to Ediacarian period likely to be 80 million years ago or earlier. They catered through a complex system of internal channels, by moving seawater.

Sponges are soft-bodied and very rarely protected as fossils, therefore finding evidence of existence is giant task. The key of their existence came to know from abnormal chemicals which is a steroids of a particular type generated sufficiently by them but virtually never by ordinary organisms.

Analysis of long strata sequence found in Oman and researchers have been able to extract these "chemical fossils" from samples spanning tens of millions of years — before, during and after the Ediacarian period.This gave clear evidence that sponges had to have evolved long before the great variety of multicellular organisms proliferated at the dawn of that time.