(LINKS TO PAST FOSSIL FRIDAYS)
Community
College (LRCCD)
Geology & Earth Science Instructor: Arthur Reed, P.G.
Happy Fossil Friday!
Friday May 7, 2021
First Multi-cellular Creatures?
MY SIMPLIFIED OVERVIEW OF LIFE’S PROGRESS ON EARTH:
Three primary steps:
1.
First single-cell
organisms around 3.6 billion years ago
2.
First algae around
1 billion years ago, likely ancestor to all plants
3.
First sponges or
worms around 650 million years ago, likely ancestor to all animals
In the study of geologic time we often speak of the
proliferation of ‘complex multicellular’ life happening with the beginning the
Paleozoic Era approx. 542 million years ago. For approx. 100 million years
before that there is evidence of multicellular life but few fossilized remains
due to lack of ‘hard parts’ in these organisms. And, the approx. 3 billion
years before that there existed only single cell organisms. There has been little in the geologic record
to help us understand the transition from single-cell to multi-cell creatures. The following recent article claims to have
found an early example of a multicellular creature all the way back to 1
billion years ago. If true, it will be
very helpful in understanding this step in our evolution.
~~
Fossil
'balls' are 1 billion years old and could be Earth's oldest known multicellular
life (LiveScience)
By Mindy Weisberger - Senior
Writer 1 day ago
The spherical
fossils came from sediments that were formerly at the bottom of a lake.
Bicellum
brasieri holotype specimen. (Image credit: Paul Strother)
Scientists have discovered
a rare evolutionary "missing link" dating to the
earliest chapter of life on Earth.
It's a microscopic, ball-shaped fossil that bridges the gap between the very
first living creatures — single-celled organisms — and more complex
multicellular life.
The spherical fossil contains two different
types of cells: round, tightly-packed cells with very thin cell walls at the
center of the ball, and a surrounding outer layer of sausage-shaped cells with
thicker walls. Estimated to be 1 billion years old, this is the oldest known
fossil of a multicellular organism, researchers reported in a new study.
Life on Earth is widely accepted as having
evolved from single-celled forms that emerged in the primordial oceans. However,
this fossil was found in sediments from the bottom of what was once a lake in
the northwest Scottish Highlands (see map below). The discovery offers a new
perspective on the evolutionary pathways that shaped multicellular life, the
scientists said in the study. PLAY SOUND
"The origins of complex multicellularity
and the origin of animals are considered two of the most important events in
the history of life on Earth," said lead study author Charles Wellman, a
professor in the Department of Animal and Plant Sciences at the University of
Sheffield in the United Kingdom.
"Our discovery sheds new light on both
of these," Sheffield said in a statement.
Today, little evidence
remains of Earth's earliest organisms. Microscopic fossils estimated to be 3.5
billion years old are credited with being the oldest fossils of life on Earth, though some experts
have questioned whether chemical clues in the so-called fossils were truly
biological in origin.
Other types of fossils
associated with ancient microbes are even older: Sediment ripples in Greenland date to 3.7 billion years
ago, and hematite tubes in Canada date between 3.77 billion
and 4.29 billion years ago. Fossils of the oldest known algae, ancestor to all of Earth's plants, are
about 1 billion years old, and the oldest sign of animal life — chemical traces
linked to ancient sponges — are at least 635 million and possible as much as
660 million years old, Live Science previously reported.
The tiny fossilized cell
clumps, which the scientists named Bicellum brasieri, were
exceptionally well-preserved in 3D, locked in nodules of phosphate minerals
that were "like little black lenses in rock strata, about one centimeter
[0.4 inches] in thickness," said lead study author Paul Strother, a
research professor in the Department of Earth and Environmental Sciences at
Boston College's Weston Observatory.
"We take those and slice them with
a diamond saw and make thin sections out of them," grinding the slices thin
enough for light to shine through — so that the 3D fossils could then be studied
under a microscope, Strother told Live Science.
The researchers found
not just one B. brasieri cell clump embedded
in phosphate, but multiple examples of spherical clumps that showed the same
dual cell structure and organization at different stages of development. This
enabled the scientists to confirm that their find was once a living organism,
Strother said.
"Bicellum" means "two-celled,"
and "brasieri" honors the late paleontologist and study co-author,
Martin Brasier. Prior to his death in 2014 in a car accident, Brasier was a
professor of paleobiology at the University of Oxford in the U.K., Strother said.
Multicellular
and mysterious
In the B. brasieri fossils, which measured about 0.001 inches
(0.03 millimeters) in diameter, the scientists saw something they had never
seen before: evidence from the fossil record marking the transition from single-celled
life to multicellular organisms. The two types of cells in B. brasieri differed from each other not only in their
shape, but in how and where they were organized in the organism's "body."
"That's something that doesn't exist
in normal unicellular organisms," Strother told Live Science. "That amount
of structural complexity is something that we normally associate with complex multicellularity,"
such as in animals, he said.
It's unknown what
type of multicellular lineage B. brasieri represents,
but its round cells lacked rigid walls, so it probably wasn't a type of algae, according
to the study. In fact, the shape and organization of its cells "is more
consistent with a holozoan origin," the authors wrote. (Holozoa is a group
that includes multicellular animals and single-celled organisms that are
animals' closest relatives).
The Scottish Highlands
site — formerly an ancient lake — where the scientists found B. brasieri presented another intriguing puzzle piece
about early evolution. Earth's oldest forms of life are typically thought to
have emerged from the ocean because most ancient fossils were preserved in marine
sediments, Strother explained. "There aren't that many lake deposits of
this antiquity, so there's a bias in the rock record toward a marine fossil
record rather than a freshwater record," he added.
B. brasieri is therefore an important
clue that ancient lake ecosystems could have been as important as the oceans
for the early evolution of life. Oceans provide organisms with a relatively
stable environment, while freshwater ecosystems are more prone to extreme
changes in temperature and alkalinity — such variations could have spurred
evolution in freshwater lakes when more complex life on Earth was in its
infancy, Strother said.
The findings were published
online April 13 in the journal Current Biology.
Originally published on Live Science.
Location map and geological
section at Lower Diabaig
Bicellum Brasieri in
mature form
Examples of the distributed
(palynological) form