Geobiology is a field of scientific research that explores the interactions between the physical Earth and the biosphere. It is a relatively young field, and its borders are fluid. There is a considerable overlap with the fields of ecology, evolutionary biology, microbiology, paleontology, and particularly soil science and biogeochemistry. Geobiology applies the principles and methods of biology, geology, and soil science to the study of the ancient history of the co-evolution of life and Earth as well as the role of life in the modern world. Geobiological 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. It differs from biogeochemistry in that the focus is on processes and organisms over space and time rather than on global chemical cycles.
Even though the terms biogeology and geobiology are often used interchangeably, they have slightly different definitions. Biogeology refers to the field of science where biological aspects of geology, or the interaction between the biosphere and lithosphere is studied. Whereas the extent of Geobiology spans much wider. The scope of geobiology has also evolved and expanded over time, now comprising secondary disciplines such as geomicrobiology, geoecology, molecular geobiology, biogeochemistry, paleobiology, applied geobiology etc.
Geobiological research synthesizes the geologic record with modern biological studies. It deals with process - how organisms affect the Earth and vice versa - as well as history - how the Earth and life have changed together. It's an all encompassing field which tries to understand the interactions between the living system and the geological and geochemical surroundings of where it evolved. Much research is grounded in the search for fundamental understanding, but geobiology can also be applied, as in the case of microbes that clean up oil spills.
Geobiology employs molecular biology, environmental microbiology, organic geochemistry, and the geologic record to investigate the evolutionary interconnectedness of life and Earth. It attempts to understand how the Earth has changed since the origin of life and what it might have been like along the way. Some definitions of geobiology even push the boundaries of this time frame - to understanding the origin of life and to the role that humans have played and will continue to play in shaping the Earth in the Anthropocene.
History
The term geobiology was coined by Lourens Baas Becking in 1934. In his words, geobiology "is an attempt to describe the relationship between organisms and the Earth," for "the organism is part of the Earth and its lot is interwoven with that of the Earth." Baas Becking's definition of geobiology was born of a desire to unify environmental biology with laboratory biology. The way he practiced it aligns closely with modern environmental microbial ecology, though his definition remains applicable to all of geobiology. In his book, Geobiology, Bass Becking stated that he had no intention of inventing a new field of study. 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, and Sergei Vinogradsky, famous for discovering lithotrophic bacteria.Winogradsky, Sergei (1887). "Über Schwefelbakterien". Bot. Zeitung (45): 489–610.
Baas Becking started writing his book Geobiologie in the late summer of 1944, when he was a prisoner of the German Kriegsmarine in Utrecht. With limited access to resources and scientific literature, he drafted the manuscript on a ledger, in barely legible handwriting. His manuscript, which he finished in just seven weeks, was heavily inspired by the works of his predecessors including Lawrence Henderson, Victor Moritz Goldschmidt, Alfred J. Lotka, Vladimir Vernadsky and Martinus Beyarink. In his book, he introduced the concept of dissipation, where he expressed his frustrations on the disastrous treatment of the earth by man. Despite being unfinished with major gaps, Baas Becking's Geobiologe is still one of the most foundational and influential works in the field of geobiology.
The first laboratory officially dedicated to the study of geobiology was the Baas Becking Geobiological Laboratory in Australia, which opened its doors in 1965. 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, thereby founding organic geochemistry and establishing the notion of biomarkers, a critical aspect of geobiology. But several decades passed before the tools were available to begin to search in earnest for chemical marks of life in the rocks. 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.Gaines, S. M. (2008). Echoes of Life: What Fossil Molecules Reveal about Earth History. Oxford University Press, USA.
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. And in the 1990s, genetics and genomics studies became possible, broadening the scope of investigation of the interaction of life and planet.
Today, geobiology has its own journals, such as Geobiology, established in 2003, and Biogeosciences, established in 2004, as well as recognition at major scientific conferences. It got its own Gordon Research Conference in 2011, a number of geobiology textbooks have been published, and many universities around the world offer degree programs in geobiology (see External links).
Major geobiological events
Perhaps the most profound geobiological event is the introduction of oxygen into the atmosphere by photosynthetic bacteria. This oxygenation of Earth's primordial atmosphere (the so-called oxygen catastrophe or Great Oxygenation Event) and the oxygenation of the oceans altered surface biogeochemical cycles and the types of organisms that have been evolutionarily selected for.
A subsequent major change was the advent of multicellularity. The presence of oxygen allowed eukaryotes and, later, multicellular life to evolve.
More anthropocentric geobiologic events include the origin of animals and the establishment of terrestrial plant life, which affected continental erosion and nutrient cycling, and likely changed the types of rivers observed, allowing channelization of what were previously predominantly braided rivers.
More subtle geobiological events include the role of termites in overturning sediments, coral reefs in depositing calcium carbonate and breaking waves, sponges in absorbing dissolved marine silica, the role of dinosaurs in breaching river levees and promoting flooding, and the role of large mammal dung in distributing nutrients.
S.G Neruchev (1927-2012), a petroleum geologist, described seventeen major geobiologic events in his 1999 paper, titled, "Periodicity of global geologic and biologic events in the Phanerozoic". He described these events chronologically, based on where black shales (organic rich, radioactive, copper, bituminous) were found.
Important concepts Geobiology is founded upon a few core concepts that unite the study of Earth and life. While there are many aspects of studying past and present interactions between life and Earth that are unclear, several important ideas and concepts provide a basis of knowledge in geobiology that serve as a platform for posing researchable questions, including the evolution of life and planet and the co-evolution of the two, genetics - from both a historical and functional standpoint, the metabolic diversity of all life, the sedimentological preservation of past life, and the origin of life.
Co-evolution of Life and Earth A core concept in geobiology is that life changes over time through evolution. The theory of evolution postulates that unique populations of organisms or species arose from genetic modifications in the ancestral population which were passed down by drift and natural selection.Darwin, C. (1859). On the origin of species London. UK: John Murray.
Along with standard biological evolution, life and planets co-evolve. Since the best adaptations are those that suit the ecological niche that the organism lives in, the physical and chemical characteristics of the environment drive the evolution of life by natural selection, but the opposite can also be true: with every advent of evolution, the environment changes.
A classic example of co-evolution is the evolution of oxygen-producing photosynthetic cyanobacteria which oxygenated Earth's Archean atmosphere. 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. During this time, around 2.4 to 2.1 billion years ago, geologic data suggests that atmospheric oxygen began to rise in what is termed the Great Oxygenation Event (GOE). It is unclear for how long cyanobacteria had been doing oxygenic photosynthesis before the GOE. Some evidence suggests there were geochemical "buffers" or sinks suppressing the rise of oxygen such as volcanism though cyanobacteria may have been around producing it before the GOE. Other evidence indicates that the rise of oxygenic photosynthesis was coincident with the GOE.
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. It may have triggered the formation of oxidized minerals and the disappearance of oxidizable minerals like pyrite from ancient stream beds. The presence of banded-iron formations (BIFs) have been interpreted as a clue for the rise of oxygen since small amounts of oxygen could have reacted with reduced ferrous iron (Fe(II)) in the oceans, resulting in the deposition of sediments containing Fe(III) oxide in places like Western Australia. However, any oxidizing environment, including that provided by microbes such as the iron-oxidizing photoautotroph Rhodopseudomonas palustris, can trigger iron oxide formation and thus BIF deposition. Other mechanisms include oxidation by UV light. Indeed, BIFs occur across large swaths of Earth's history and may not correlate with only one event.
Pyrite has been hypothesized as the first source of energy that paved the way of life formation. In Early earth, and even now, phosphate was generally considered a limiting nutrient for life. Pyrite, being positively charged, can concentrate anionic phosphate and phosphorylated organic molecules. The free energy yield from anaerobic biomineralization of pyrites by chemoautotrophs is enough for supporting life.
Some scientists have also proposed that clay minerals facilitated the origin of life. Clay and clay minerals, such as kaolinite and montmorillonite, have been widely distributed in geologic time and space. Clay mineral surfaces concentrated simple organic molecules and protected and preserved them. This process could also occur on other planets, comets, meteorites and asteroids.