Life of the Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 142

placozoans feed by ingesting organic debris as they move along.
Perhaps flat animals, and not sponges, represent the beginnings of a
multicellular world? With no fossil record, this remains speculation.
The Quilt Creatures
For over 3 billion years, the oceans stirred only to the sound of flatu-
lent microbes releasing bubbles of gas from the seabed as by-products
of respiration. Over much of the sea floor there were thin slimy con-
structions a few centimetres thick, colonized and built by archaea and
bacteria. Although thin, these bacterial mats presented a barrier
between the water above and the sediment below, and the sediment
remained the realm of sulphate-reducing microbes, existing in an
environment with no oxygen. Above the mats, sponges had begun to
colonize the ocean floor, rising to exploit the supply of organic mate-
rial in the water just above the seabed. Into this world of microbial
mats and sponges came the multicellular Ediacarans, a striking array
of new organisms that were a global phenomenon from about 600
million years ago, and which are found in rocks worldwide from
Australia to Canada.
The Ediacarans have puzzled scientists since their first discovery,
by serendipity, in the county of Leicestershire, England, by James
Harley and John Plant in the spring of 1848 86 (forgotten to science,
these fossils were then rediscovered 110 years later by schoolboy Roger
Mason and Leicester academic Trevor Ford). On a journey to the
ruined Leicester Abbey—one of those razed to the ground by Henry
VIII's dissolution of the monasteries—Harley and Plant stopped to
visit a recently disused quarry in the area now known as Bradgate
Park, where they noticed strange circular marks on the Precambrian
slates, which they likened in shape to ammonites. The two travellers
had discovered fossils in rocks where science then said no fossils
could be found.