Geobiology

[2] Geobiologic studies tend to be focused on microorganisms, and on the role that life plays in altering the chemical and physical environment of the pedosphere, which exists at the intersection of the lithosphere, atmosphere, hydrosphere and/or cryosphere.

[3] Geobiology employs molecular biology, environmental microbiology, organic geochemistry, and the geologic record to investigate the evolutionary interconnectedness of life and Earth.

[4] Baas Becking's understanding of geobiology was heavily influenced by his predecessors, including Martinus Beyerinck, his teacher from the Dutch School of Microbiology.

Others included Vladimir Vernadsky, who argued that life changes the surface environment of Earth in The Biosphere, his 1926 book,[5] and Sergei Vinogradsky, famous for discovering lithotrophic bacteria.

[4] However, it took another 40 or so years for geobiology to become a firmly rooted scientific discipline, thanks in part to advances in geochemistry and genetics that enabled scientists to begin to synthesize the study of life and planet.

In the 1930s, Alfred Treibs discovered chlorophyll-like porphyrins in petroleum, confirming its biological origin,[7] thereby founding organic geochemistry and establishing the notion of biomarkers, a critical aspect of geobiology.

In the 1970s and '80s, scientists like Geoffrey Eglington and Roger Summons began to find lipid biomarkers in the rock record using equipment like GCMS.

[8] On the biology side of things, in 1977, Carl Woese and George Fox published a phylogeny of life on Earth, including a new domain - the Archaea.

The ancestors of cyanobacteria began using water as an electron source to harness the energy of the sun and expelling oxygen before or during the early Paleoproterozoic.

[23] The presence of oxygen on Earth from its first production by cyanobacteria to the GOE and through today has drastically impacted the course of evolution of life and planet.

Earth acquired a magnetic field about 3.4 Ga[37] that has undergone a series of geomagnetic reversals on the order of millions of years.

[43] Comparing DNA sequences alone gives a record of the history of evolution with an arbitrary measure of phylogenetic distance “dating” that last common ancestor.

However, if information about the rate of genetic mutation is available or geologic markers are present to calibrate evolutionary divergence (i.e. fossils), we have a timeline of evolution.

Searching for similar genes in other organisms and in metagenomic and metatranscriptomic data allows us to understand what processes could be relevant and important in a given ecosystem, providing insight into the biogeochemical cycles in that environment.

[53] While animals such as ourselves are limited to aerobic respiration, other organisms can "breathe" sulfate (SO42-), nitrate (NO3-), ferric iron (Fe(III)), and uranium (U(VI)), or live off energy from fermentation.

[8] The sedimentary record allows scientists to observe changes in life and Earth in composition over time and sometimes even date major transitions, like extinction events.

[55] While geobiology is a diverse and varied field, encompassing ideas and techniques from a wide range of disciplines, there are a number of important methods that are key to the study of the interaction of life and Earth that are highlighted here.

Some practitioners take a very broad view of its boundaries, encompassing many older, more established fields such as biogeochemistry, paleontology, and microbial ecology.

Astrobiology is an interdisciplinary field that uses a combination of geobiological and planetary science data to establish a context for the search for life on other planets.

In addition, astrobiologists research the possibility of life based on other metabolisms and elements, the survivability of Earth's organisms on other planets or spacecraft, planetary and solar system evolution, and space geochemistry.

[57] Biogeochemistry is a systems science that synthesizes the study of biological, geological, and chemical processes to understand the reactions and composition of the natural environment.

Geobiochemistry is founded on the notion that life is a planetary response because metabolic catalysis enables the release of energy trapped by a cooling planet.

Microbial ecology is similar, but tend to focus more on lab studies and the relationships between organisms within a community, as well as within the ecosystem of their chemical and geological physical environment.

While it is generally reliant on the tools of microbiology, microbial geochemistry uses geological and chemical methods to approach the same topic from the perspective of the rocks.

Geomicrobiology and microbial geochemistry (GMG) is a relatively new interdisciplinary field that more broadly takes on the relationship between microbes, Earth, and environmental systems.

Billed as a subset of both geobiology and geochemistry, GMG seeks to understand elemental biogeochemical cycles and the evolution of life on Earth.

Specifically, it asks questions about where microbes live, their local and global abundance, their structural and functional biochemistry, how they have evolved, biomineralization, and their preservation potential and presence in the rock record.

Molecules like sterols and hopanoids, membrane lipids found in eukaryotes and bacteria, respectively, can be preserved in the rock record on billion-year timescales.

Following the death of the organism they came from and sedimentation, they undergo a process called diagenesis whereby many of the specific functional groups from the lipids are lost, but the hydrocarbon skeleton remains intact.

[63] The search for molecular fossils, such as lipid biomarkers like steranes and hopanes, has also played an important role in geobiology and organic geochemistry.

The colorful microbial mats of Grand Prismatic Spring in Yellowstone National Park , USA. The orange mats are composed of Chloroflexia , " Cyanobacteria ", and other organisms that thrive in the 70˚C water. Geobiologists often study extreme environments like this because they are home to extremophilic organisms. It has been hypothesized that these environments may be representative of early Earth. [ 1 ]
A microbial mat in White Creek, Yellowstone National Park , USA. Note the conical microstructure of the bacterial communities. These are hypothesized to be a living analogue of ancient fossil stromatolites . Each cone has an oxygen gas bubble on top, the product of oxygenic photosynthesis by cyanobacteria in the multi-species microbial mats .
The geologic timescale overlain with major geobiologic events and occurrences. The oxygenation of the atmosphere is shown in blue starting 2.4 Ga, although the exact dating of the Great Oxygenation Event is debated. [ 14 ]
Banded iron formation (BIF), Hammersley Formation , Western Australia
Modern, living stromatolites in Shark Bay, Australia. Shark Bay is one of the few places in the world where stromatolites can be seen today, though they were likely common in ancient shallow seas before the rise of metazoan predators.
A phylogenetic tree of living things, based on rRNA data and proposed by Carl Woese , showing the separation of bacteria , archaea , and eukaryotes and linking the three branches of living organisms to the LUCA (the black trunk at the bottom of the tree).
3.4 billion year-old stromatolites from the Warrawoona Group , Western Australia . While the origin of Precambrian stromatolites is a heavily debated topic in geobiology, [ 50 ] stromatolites from Warrawoona are hypothesized to have been formed by ancient communities of microbes. [ 51 ]
"Giant" ooids of the Johnnie Formation in the Death Valley area, California, USA. Ooids are near-spheroidal calcium carbonate grains that accumulate around a central nucleus and can be sedimented to form oolite like this. Microbes can mediate the formation of ooids. [ 50 ]
A microbial mat growing on acidic soil in Norris Geyser basin , Yellowstone National Park , USA. The black top serves as a sort of sunscreen, and when you look underneath you see the green cyanobacteria .
Stromatolites in the Green River Shale, Wyoming , USA, dating to the Eocene
A vertical cross section of a microbial mat containing different organisms that perform different metabolisms . The green are presumably cyanobacteria , and teepee-like microstructures are visible on the surface.
Ediacaran fossils from Mistaken Point , Newfoundland. Ediacaran biota originated during the Ediacaran Period and are unlike most animals around today.