Living Fossils

Located in Hamelin’s Pool, a shallow area of Shark Bay in Western Australia, these odd formations aren’t rocks—they’re stromatolites, and they were built over millennia by single-celled cyanobacteria (also known as blue-green algae). 4,000 to 6,000 years ago, a huge bank of seagrass began to block the tidal flow into Hamelin’s Pool, which meant that the water became twice as salty as the open ocean. Animals like snails and chitons that would usually feed on the algae couldn’t survive, so the blue-green algae began to flourish. Gathered in colonies, they trapped sediment with their sticky surface coatings. This sediment reacted with calcium carbonate in the water and formed limestone, essentially creating a living fossil—this limestone is alive, its top surface layer teeming with active cyanobacteria. The limestone builds up slowly at a rate of about 1mm per year. The stromatolites in Shark Bay are estimated to be between 3,000 and 2,000 years old, but they’re similar to life forms in Precambrian times, 3.5 billion years ago, at the dawn of complex organisms. There are over 50 kinds of cyanobacteria in Shark Bay, and one is thought to have descended from an organism that lived nearly 2 million years ago, making it a part of one of the longest biological lineages.

(Image Credit: 1, 2)

The Archean World, Peter Sawyer, The Smithsonian Institution

In the Archean, life is at its purest. No courtship, no conflict, no sleep, no song, no fear, no lust—just organisms, simplified to abstraction, thriving in poison, water, and ash. Life is not a substance, but a process: consume and continue.

Thermophiliacs feast on hot spring chemicals, relishing the heavy stink of sulphur, and kaleidoscope the steaming pool’s edges. Elsewhere, stromatolites, shallow-water plateaus of sediment and biofilm, learn photosynthesis, change the atmosphere, and terraform the dawn planet. 

The microbes are oblivious to anything outside of their own homeostasis, yet assemble into communities, unknowingly nestling cell walls against each other. Millions of lives surround each bacteria, but they only know their own, like a man running through the streets of Prague, bumping elbows with a thousand other lives—each rich with hope and love and loss—but thinking only of catching the 207 bus on time.

Earliest Evidence of Life Found in Australia

by PhysOrg staff

A group of US researchers studying some of the oldest rocks in the world in the Pilbara region of Western Australia, say they have found the oldest traces of life on Earth, dated at 3.49 billion years old.

The scientists, led by Associate Professor Nora Noffke of the Old Dominion University in Norfolk, Virginia, did not strictly find fossils of that age, but actually found web-like patterns criss-crossing the surfaces of the Pilbara sandstone. Dr. Noffke calls the patterns and textures Microbially Induced Sedimentary Structures (MISS) and said the structures were created by a complete ecosystem of different types of bacteria living in the Archean eon (roughly 3.8 to 2.5 GA) almost three-and-a-half billion years ago.

The Pilbara region is a popular area for scientists searching for traces of early life on the planet because the ancient sedimentary rocks are extremely well preserved. The rocks were originally sand, and the region was originally a coastal plain. The sand was then built up into microbial mats by microbes, and over time the sand turned to rock and preserved the bacterial mats and structures such as MISS…

(read more: PhysOrg)                               (photoL: Paul Harrison)

Scientists Solve Disappearance of Stromatolites Mystery

The widespread disappearance of stromatolites, the earliest visible manifestation of life on Earth, may have been driven by single-celled organisms called foraminifera.

The findings, by scientists at Woods Hole Oceanographic Institution (WHOI); Massachusetts Institute of Technology; the Univ. of Connecticut; Harvard Medical School; and Beth Israel Deaconess Medical Center, were published online this week in the Proceedings of the National Academy of Sciences.

Read more:

What Doomed the Stromatolites? - Scientists find key clue to an ancient enigma

by Cherie Winner

About a billion years before the dinosaurs became extinct, stromatolites roamed the Earth until they mysteriously disappeared. Well, not roamed exactly. 

Stromatolites (“layered rocks”) are rocky structures made by photosynthetic cyanobacteria. The microbes secrete sticky compounds that bind together sediment grains, creating a mineral “microfabric” that accumulates in fine layers. Massive formations of stromatolites showed up along shorelines all over the world about 3.5 billion years ago. They were the earliest visible manifestation of life on Earth and dominated the scene for more than two billion years. 

“They were one of the earliest examples of the intimate connection between biology—living things—and geology—the structure of the Earth itself,” said Joan Bernhard, a geobiologist at Woods Hole Oceanographic Institution (WHOI). “Then, around one billion years ago, their diversity and abundance begin to take a nosedive.” …

(read more: Oceanus - WHOI)

Delightful stromatolite

This layered rock is a 2.2. billion year old fossil from Bolivia. These layers are the characteristic shape of stromatolites, formed by alternating layers of sediment and microscopic organisms. 

As the organism or organisms grow upwards, they changed the chemistry of the waters around them, causing sediment to stick and sometimes to harden. In samples this old, its difficult to figure out exactly which species were present in any stromatolite or what role they served. Modern day stromatolites tend to have a variety of species, which alternate their growth depending on the chemistry and the availability of food.

Colonies like these were likely hosts of cyanobacteria, which helped build up oxygen in the early Earth’s atmosphere, and are a possible place where eukaryotic organisms and even multicellular life could have first evolved.


Image credit:

Read more:


A continuation of the fossil parade with younger fossils!

Turritella agates (the youngest of my current fossils, around 46 mya), sea sediment jasper (bits of crinoids and other fossil jumbles that sank to the bottom), fossilized coral, stromatolites (basically pond scum, but the pond scum that helped oxygenate the atmosphere and create an earth habitable to species than then ate it and took over the planet).

Single-Cell Smackdown: The Battle for Earth’s Early Oceans

by Becky Oskin

For 2 billion years stromatolites ruled the fossil record, dominating shallow-water environments everywhere on Earth. But, long before algae-munching animals appeared 550 million years ago, stromatolites mysteriously plummeted in number, and now scientists think they’ve found a possible culprit…

(read more :Live Science)

(photo: stromatolites in Sharks Bay, Australia, one of the few places on Earth where these living fossils survive, by Virginia Edgcomb, WHOI)


Lab coat commission for a biologist!

Depicts the strata and fossils of the Front Range of Colorado, as well as the DNA encoding strand for hemoglobin.

Calamites -
Dinosaur Ridge -
Fountain Fmt -
Morrison Fmt -
Paleobiology - Historical Geology Notes, Dr. Jennifer Stempien, Lecturer Spring 2012, CU Boulder Geology Dept.
Paleobiology - “A Correlated History of Earth” poster by Pan Terra Inc.
Strata Summary -
Strata Summary -
Strata Summary -