2.5B-year-old fossils of bacteria that predate the formation of oxygen
The Geek Keep: 2.5 billion-year-old fossils of bacteria that predate the formation of oxygen


                     
                            
                                
                                    
    

A microscopic image of 2.5 billion-year-old sulfur-oxidizing 
bacterium. Credit: Andrew Czaja, UC assistant professor of geology
    



        Somewhere between Earth's creation and 
where we are today, scientists have demonstrated that some early life 
forms existed just fine without any oxygen.
                                
                                        While 
researchers proclaim the first half of our 4.5 billion-year-old planet's
 life as an important time for the development and evolution of early 
bacteria, evidence for these life forms remains sparse including how 
they survived at a time when oxygen levels in the atmosphere were less 
than one-thousandth of one percent of what they are today.

Recent geology research from the University of Cincinnati presents 
new evidence for bacteria found fossilized in two separate locations in 
the Northern Cape Province of South Africa.

"These are the oldest reported fossil sulfur bacteria to date," says 
Andrew Czaja, UC assistant professor of geology. "And this discovery is 
helping us reveal a diversity of life and ecosystems that existed just 
prior to the Great Oxidation Event, a time of major atmospheric 
evolution."

The 2.52 billion-year-old sulfur-oxidizing bacteria are described by 
Czaja as exceptionally large, spherical-shaped, smooth-walled 
microscopic structures much larger than most modern bacteria, but 
similar to some modern single-celled organisms that live in deepwater 
sulfur-rich ocean settings today, where even now there are almost no 
traces of oxygen.


    

UC Professor Andrew Czaja indicates the layer of rock from which
 fossil bacteria were collected on a 2014 field excursion near the town 
of Kuruman in the Northern Cape Province of South Africa. Credit: Aaron 
Satkoski, UWM postdoc on the excursion.
    



        In his research published in the December issue of the journal Geology
 of the Geological Society of America, Czaja and his colleagues Nicolas 
Beukes from the University of Johannesburg and Jeffrey Osterhout, a 
recently graduated master's student from UC's department of geology, 
reveal samples of bacteria that were abundant in deep water areas of the
 ocean in a geologic time known as the Neoarchean Eon (2.8 to 2.5 
billion years ago).

"These fossils represent the oldest known organisms that lived in a 
very dark, deep-water environment," says Czaja. "These bacteria existed 
two billion years before plants and trees, which evolved about 450 
million years ago. We discovered these microfossils preserved in a layer
 of hard silica-rich rock called chert located within the Kaapvaal 
craton of South Africa."

With an atmosphere of much less than one percent oxygen, scientists 
have presumed that there were things living in deep water in the mud 
that didn't need sunlight or oxygen, but Czaja says experts didn't have 
any direct evidence for them until now.

                                        
Czaja argues that finding rocks this old is rare, so researchers' 
understanding of the Neoarchean Eon are based on samples from only a 
handful of geographic areas, such as this region of South Africa and 
another in Western Australia.


    
    
    

    

    
    

According to Czaja, scientists through the years have theorized that 
South Africa and Western Australia were once part of an ancient 
supercontinent called Vaalbara, before a shifting and upending of 
tectonic plates split them during a major change in the Earth's surface.

Based on radiometric dating and geochemical isotope analysis, Czaja 
characterizes his fossils as having formed in this early Vaalbara 
supercontinent in an ancient deep seabed containing sulfate from 
continental rock. According to this dating, Czaja's fossil bacteria were
 also thriving just before the era when other shallow-water bacteria 
began creating more and more oxygen as a byproduct of photosynthesis.

"We refer to this period as the Great Oxidation Event that took place 2.4 to 2.2 billion years ago," says Czaja.
    

Microstructures here have physical characteristics consistent 
with the remains of compressed coccodial (round) bacteria 
microorganisms. Credit: Andrew Czaja, permission to publish by 
Geological Society of America
    



        Early recycling

Czaja's fossils show the Neoarchean bacteria in plentiful numbers 
while living deep in the sediment. He contends that these early bacteria
 were busy ingesting volcanic hydrogen sulfide—the molecule known to 
give off a rotten egg smell—then emitting sulfate, a gas that has no 
smell. He says this is the same process that goes on today as modern 
bacteria recycle decaying organic matter into minerals and gases.

"The waste product from one [bacteria] was food for the other," adds Czaja.

"While I can't claim that these early bacteria are the same ones we 
have today, we surmise that they may have been doing the same thing as 
some of our current bacteria," says Czaja. "These early bacteria likely 
consumed the molecules dissolved from sulfur-rich minerals that came 
from land rocks that had eroded and washed out to sea, or from the 
volcanic remains on the ocean's floor.

There is an ongoing debate about when sulfur-oxidizing bacteria arose
 and how that fits into the earth's evolution of life, Czaja adds. "But 
these fossils tell us that sulfur-oxidizing bacteria were there 2.52 billion years ago, and they were doing something remarkable."

credit; Melanie Schefft
                      
                  
                 