9.4 Biogeochemical evolution

Biogeochemical evolution shaped Earth's environment through complex interactions between geological processes and life. From the primordial atmosphere to the Great Oxidation Event, these changes laid the foundation for modern biogeochemical cycles and ecosystems.

Understanding this evolution provides crucial insights into Earth's history and future. It reveals how life and the environment co-evolved, creating the conditions that support modern biodiversity and influencing global climate patterns we see today.

Early Earth conditions

• Biogeochemical evolution shaped Earth's early environment through complex interactions between geological processes and emerging life forms
• Understanding early Earth conditions provides crucial insights into the foundations of modern biogeochemical cycles and their impact on global ecosystems

Primordial atmosphere composition

Top images from around the web for Primordial atmosphere composition

• 

  Atmosphere of Earth - Wikipedia View original

  Is this image relevant?

• 

  Atmospheric Gasses | Physical Geography View original

  Is this image relevant?

• 

  Biogeochemical Cycles · Biology View original

  Is this image relevant?

• 

  Atmosphere of Earth - Wikipedia View original

  Is this image relevant?

• 

  Atmospheric Gasses | Physical Geography View original

  Is this image relevant?

1 of 3

Top images from around the web for Primordial atmosphere composition

• 

  Atmosphere of Earth - Wikipedia View original

  Is this image relevant?

• 

  Atmospheric Gasses | Physical Geography View original

  Is this image relevant?

• 

  Biogeochemical Cycles · Biology View original

  Is this image relevant?

• 

  Atmosphere of Earth - Wikipedia View original

  Is this image relevant?

• 

  Atmospheric Gasses | Physical Geography View original

  Is this image relevant?

1 of 3

• Consisted primarily of hydrogen, helium, methane, ammonia, and water vapor
• Lacked free oxygen, creating a reducing environment conducive to prebiotic chemistry
• Gradually evolved through volcanic outgassing and impacts from comets and asteroids
• Atmospheric pressure significantly higher than present-day levels due to increased CO2 content

Formation of oceans

• Occurred through a combination of volcanic outgassing and delivery of water by comets and asteroids
• Condensation of water vapor as Earth's surface cooled below 100°C
• Early oceans were likely acidic due to dissolved CO2 and other volcanic gases
• Provided a crucial medium for prebiotic chemical reactions and the emergence of life
  • Facilitated concentration and interaction of organic molecules
  • Offered protection from harmful UV radiation

Prebiotic chemistry

• Involves the synthesis of complex organic molecules from simpler precursors in the absence of life
• Miller-Urey experiment demonstrated the formation of amino acids under simulated early Earth conditions
• Key processes include:
  • Polymerization of simple organic molecules into more complex structures
  • Formation of lipid membranes, crucial for the development of cellular life
  • Concentration of organic molecules in hydrothermal vents or clay minerals
• Potential role of extraterrestrial organic matter delivered by comets and meteorites

Origin of life

• Marks the transition from prebiotic chemistry to self-replicating, evolving systems
• Understanding the origin of life is crucial for interpreting the early stages of biogeochemical evolution and the development of Earth's ecosystems
• Provides insights into the potential for life on other planets and the universality of biological processes

RNA world hypothesis

• Proposes that self-replicating RNA molecules preceded the development of DNA and proteins
• RNA serves dual roles as both genetic material and catalytic molecules (ribozymes)
• Key features of the RNA world:
  • RNA-based replication and catalysis
  • Gradual evolution of more complex RNA structures
  • Transition to DNA-based genetic storage and protein-based catalysis
• Supported by the discovery of ribozymes in modern organisms and laboratory experiments demonstrating RNA self-replication

First cellular organisms

• Emerged approximately 3.5-3.8 billion years ago
• Likely prokaryotic in nature, lacking a membrane-bound nucleus
• Key characteristics:
  • Lipid membrane encapsulating genetic material and metabolic machinery
  • Ability to maintain homeostasis and respond to environmental stimuli
  • Capacity for energy production and self-replication
• Diversified into two main domains: Bacteria and Archaea
  • Distinct cell membrane compositions and metabolic pathways
  • Adaptation to various environmental niches (extremophiles)

Microbial mats vs stromatolites

• Microbial mats
  • Layered communities of microorganisms, often dominated by photosynthetic bacteria
  • Form in various aquatic environments (shallow marine, hypersaline lakes)
  • Play crucial roles in nutrient cycling and sediment stabilization
  • Modern examples include cyanobacterial mats in Shark Bay, Australia
• Stromatolites
  • Layered sedimentary structures formed by the trapping and binding of sediment by microbial mats
  • Represent some of the oldest evidence of life on Earth (dating back 3.5 billion years)
  • Provide insights into ancient microbial communities and environmental conditions
  • Notable examples found in Shark Bay, Australia, and Yellowstone National Park, USA
• Differences between microbial mats and stromatolites:
  • Stromatolites involve mineral precipitation and sediment trapping, while mats may not
  • Stromatolites form distinct, often dome-shaped structures, while mats are typically flat
  • Stromatolites preserve a record of microbial activity over time, while mats represent active communities

Great Oxidation Event

• Marks a pivotal moment in Earth's biogeochemical evolution, fundamentally altering the planet's atmosphere and biosphere
• Occurred approximately 2.4-2.1 billion years ago, transforming Earth from a reducing to an oxidizing environment
• Profoundly impacted the evolution of life and the cycling of elements in the Earth system

Rise of photosynthesis

• Emerged in cyanobacteria around 3 billion years ago
• Oxygenic photosynthesis uses water as an electron donor, producing oxygen as a byproduct
• Key components of the photosynthetic process:
  • Light-harvesting complexes (chlorophyll)
  • Electron transport chain
  • Calvin cycle for carbon fixation
• Gradually increased atmospheric oxygen levels over hundreds of millions of years
  • Initially, oxygen was consumed by reduced minerals in the oceans and on land
  • Eventual saturation of oxygen sinks led to atmospheric accumulation

Oxygen accumulation in atmosphere

• Atmospheric oxygen levels increased from <0.001% to >1% during the Great Oxidation Event
• Caused major changes in Earth's geochemistry and biology:
  • Oxidation of reduced minerals (iron, sulfur) in oceans and on land
  • Formation of the ozone layer, protecting life from harmful UV radiation
  • Development of aerobic respiration in organisms, enabling more efficient energy production
• Triggered a mass extinction of anaerobic organisms unable to cope with oxygen toxicity
  • Survival of some anaerobes in oxygen-poor environments (deep ocean, sediments)
• Led to the evolution of more complex life forms, including eukaryotes

Banded iron formations

• Distinctive sedimentary rocks characterized by alternating layers of iron-rich and silica-rich minerals
• Formed primarily between 3.8 and 1.8 billion years ago, with peak deposition around the time of the Great Oxidation Event
• Key features and significance:
  • Indicate the presence of dissolved iron in early oceans
  • Reflect the gradual oxygenation of the atmosphere and oceans
  • Serve as important economic sources of iron ore (Hamersley Basin, Australia)
• Formation process:
  • Photosynthetic bacteria release oxygen, oxidizing dissolved iron in seawater
  • Precipitated iron oxides settle to the seafloor, alternating with silica-rich layers
  • Cyclical nature of deposition may reflect seasonal or longer-term variations in biological activity or ocean chemistry

Evolution of biogeochemical cycles

• Describes the development and interconnection of elemental cycles crucial for life and Earth system functioning
• Reflects the co-evolution of life and the environment over geological time scales
• Understanding these cycles is essential for interpreting Earth's history and predicting future environmental changes

Carbon cycle development

• Evolved from a predominantly abiotic cycle to one heavily influenced by biological processes
• Key stages in carbon cycle evolution:
  • Early carbon dioxide-rich atmosphere and oceans
  • Development of photosynthesis and carbon fixation by microorganisms
  • Emergence of carbonate biomineralization (shells, skeletons)
  • Burial of organic carbon in sediments, leading to long-term carbon sequestration
• Modern carbon cycle components:
  • Atmospheric CO2 exchange with oceans and terrestrial biosphere
  • Weathering of silicate rocks as a long-term CO2 sink
  • Volcanic and metamorphic CO2 emissions balancing long-term sinks

Nitrogen cycle emergence

• Developed as life evolved to utilize nitrogen in various forms
• Key processes in the nitrogen cycle:
  • Nitrogen fixation by specialized microorganisms (diazotrophs)
  • Nitrification: conversion of ammonia to nitrate by chemolithotrophic bacteria
  • Denitrification: reduction of nitrate to nitrogen gas by anaerobic bacteria
  • Anammox: anaerobic ammonium oxidation, discovered in the 1990s
• Evolution of nitrogen cycle components:
  • Early nitrogen fixation by abiotic processes (lightning) and primitive microorganisms
  • Diversification of nitrogen-cycling microorganisms and metabolic pathways
  • Development of symbiotic relationships (legumes and nitrogen-fixing bacteria)
  • Anthropogenic impacts on the nitrogen cycle through fertilizer use and fossil fuel combustion

Sulfur cycle changes

• Underwent significant changes throughout Earth's history, closely linked to oxygen levels
• Key stages in sulfur cycle evolution:
  • Predominance of reduced sulfur species in early anoxic oceans
  • Gradual oxidation of sulfur with increasing atmospheric oxygen
  • Development of sulfate reduction by anaerobic microorganisms
  • Emergence of sulfur oxidation pathways in chemolithotrophic bacteria
• Modern sulfur cycle components:
  • Weathering of sulfur-containing rocks
  • Biological sulfate reduction in anoxic environments
  • Volcanic sulfur emissions
  • Anthropogenic sulfur pollution and acid rain formation
• Sulfur isotopes as indicators of past environmental conditions and microbial activity

Paleoenvironmental proxies

• Provide crucial information about past environmental conditions and biogeochemical processes
• Allow reconstruction of Earth's climate, ocean chemistry, and ecosystem dynamics over geological time scales
• Essential for understanding long-term trends and natural variability in the Earth system

Stable isotope ratios

• Measure variations in the relative abundance of stable isotopes of elements (C, O, N, S)
• Reflect biological, chemical, and physical processes in past environments
• Key applications in paleoenvironmental studies:
  • δ13C: indicates carbon sources, productivity, and ocean circulation patterns
  • δ18O: serves as a proxy for temperature and global ice volume
  • δ15N: provides information on nutrient cycling and food web structure
  • δ34S: reflects sulfur cycling and redox conditions in past oceans
• Analytical techniques:
  • Mass spectrometry for precise measurement of isotope ratios
  • Microsampling methods for high-resolution temporal records (foraminifera shells)

Trace element distributions

• Analyze concentrations and ratios of trace elements in geological materials
• Provide insights into past environmental conditions and biogeochemical processes
• Key trace element proxies:
  • Mg/Ca ratios in carbonate shells: indicator of past ocean temperatures
  • Cd/Ca ratios: proxy for past ocean nutrient concentrations
  • Rare earth elements (REEs): indicators of ocean circulation and redox conditions
  • Redox-sensitive elements (U, Mo, V): reflect past ocean oxygenation states
• Analytical methods:
  • Inductively coupled plasma mass spectrometry (ICP-MS) for precise elemental analysis
  • Laser ablation techniques for high-resolution spatial mapping of trace elements

Molecular fossils

• Organic compounds preserved in sediments that retain information about their biological sources
• Provide insights into past ecosystems, environmental conditions, and evolutionary events
• Types of molecular fossils:
  • Lipid biomarkers (steranes, hopanes): indicate sources of organic matter and environmental conditions
  • Pigments (chlorophylls, carotenoids): reflect past primary productivity and phototrophic communities
  • Amino acids: provide information on protein preservation and diagenesis
  • Ancient DNA: offers direct evidence of past biodiversity and evolutionary relationships
• Analytical techniques:
  • Gas chromatography-mass spectrometry (GC-MS) for biomarker identification and quantification
  • High-performance liquid chromatography (HPLC) for pigment analysis
  • Polymerase chain reaction (PCR) and next-generation sequencing for ancient DNA analysis

Mass extinctions

• Represent periods of elevated extinction rates affecting a wide range of taxa across the globe
• Profoundly impact ecosystem structure, biogeochemical cycles, and evolutionary trajectories
• Understanding mass extinctions provides insights into ecosystem resilience and potential future scenarios

Causes and consequences

• Multiple potential triggers for mass extinctions:
  • Bolide impacts (Cretaceous-Paleogene extinction)
  • Volcanic eruptions and associated climate changes (End-Permian extinction)
  • Rapid climate shifts (End-Ordovician extinction)
  • Ocean anoxia and euxinia (Frasnian-Famennian extinction)
• Consequences of mass extinctions:
  • Dramatic reductions in biodiversity across multiple trophic levels
  • Disruption of ecosystem functions and biogeochemical cycles
  • Opening of ecological niches for surviving and newly evolving species
  • Long-term changes in evolutionary trajectories and ecosystem structure

Biogeochemical perturbations

• Mass extinctions often associated with significant disruptions to global biogeochemical cycles
• Key biogeochemical indicators of extinction events:
  • Carbon isotope excursions: reflect changes in primary productivity and carbon burial
  • Sulfur isotope anomalies: indicate shifts in ocean redox conditions and sulfur cycling
  • Trace metal enrichments: suggest widespread ocean anoxia or euxinia
  • Nitrogen isotope perturbations: reflect changes in nutrient cycling and marine productivity
• Feedback mechanisms between biotic crises and biogeochemical cycles:
  • Collapse of primary productivity leading to carbon cycle imbalances
  • Release of methane hydrates amplifying climate change
  • Ocean acidification impacting carbonate-secreting organisms

Recovery and diversification

• Post-extinction recovery periods characterized by ecosystem reorganization and adaptive radiation
• Timescales of recovery vary depending on extinction magnitude and environmental conditions
  • Rapid recovery (thousands of years) for some ecosystem components
  • Prolonged recovery (millions of years) for pre-extinction levels of biodiversity
• Key aspects of post-extinction recovery:
  • Survival of "disaster taxa" adapted to perturbed environments
  • Gradual reestablishment of complex food webs and ecosystem functions
  • Evolution of novel morphologies and ecological strategies (Cambrian Explosion)
  • Shifts in dominant taxonomic groups (rise of mammals after K-Pg extinction)
• Importance of understanding recovery processes for predicting future ecosystem responses to global change

Anthropogenic impacts

• Human activities have become a dominant force shaping Earth's biogeochemical cycles and ecosystems
• Understanding anthropogenic impacts is crucial for developing sustainable management strategies and predicting future environmental changes
• Geochemistry plays a key role in quantifying and tracking human-induced changes to the Earth system

Industrial revolution effects

• Marked a significant shift in human impact on the environment, beginning in the late 18th century
• Key environmental changes associated with industrialization:
  • Increased atmospheric CO2 concentrations due to fossil fuel combustion
  • Release of pollutants (sulfur dioxide, heavy metals) from industrial processes
  • Land use changes and deforestation for agriculture and urban development
  • Alteration of hydrological cycles through dam construction and water diversion
• Geochemical signatures of the Industrial Revolution:
  • Rise in atmospheric CO2 recorded in ice cores and tree rings
  • Heavy metal pollution in lake sediments and polar ice
  • Changes in nitrogen isotope ratios reflecting increased fertilizer use

Global warming vs climate change

• Global warming: refers specifically to the increase in Earth's average surface temperature
  • Primarily driven by increased greenhouse gas concentrations in the atmosphere
  • Observed temperature increase of approximately 1°C since pre-industrial times
  • Impacts include melting ice sheets, sea-level rise, and increased frequency of extreme weather events
• Climate change: encompasses broader changes in the Earth's climate system
  • Includes changes in precipitation patterns, wind patterns, and ocean circulation
  • Affects ecosystems, agriculture, and human societies on a global scale
  • Involves complex feedbacks between the atmosphere, oceans, and biosphere
• Geochemical approaches to studying climate change:
  • Stable isotope analysis of ice cores, tree rings, and marine sediments
  • Trace element analysis in coral skeletons and mollusk shells
  • Biomarker analysis in sedimentary records

Ocean acidification

• Refers to the ongoing decrease in ocean pH due to absorption of atmospheric CO2
• Represents a major threat to marine ecosystems and biogeochemical cycles
• Key aspects of ocean acidification:
  • Decrease in carbonate ion concentrations, impacting calcifying organisms
  • Potential disruption of marine food webs and ecosystem functions
  • Alteration of nutrient cycling and trace metal availability in seawater
• Geochemical approaches to studying ocean acidification:
  • Boron isotope analysis in coral skeletons as a proxy for seawater pH
  • Trace element ratios in foraminifera shells reflecting carbonate chemistry
  • Monitoring of dissolved inorganic carbon and alkalinity in seawater

Future biogeochemical scenarios

• Projecting potential changes in Earth's biogeochemical cycles under various human impact scenarios
• Crucial for informing policy decisions and developing strategies for environmental management
• Requires integration of geochemical data, Earth system models, and socioeconomic factors

Potential tipping points

• Represent critical thresholds in Earth system components that, when crossed, lead to rapid and potentially irreversible changes
• Key potential tipping points in the Earth system:
  • Amazon rainforest dieback: transition from rainforest to savanna ecosystem
  • Melting of Arctic sea ice: altering global heat distribution and ocean circulation
  • Permafrost thaw: releasing stored carbon and methane into the atmosphere
  • Collapse of Atlantic Meridional Overturning Circulation: disrupting global climate patterns
• Geochemical approaches to identifying and studying tipping points:
  • Analysis of past abrupt climate changes in paleoclimate records
  • Monitoring of early warning signals in environmental time series data
  • Development of high-resolution proxies for rapid environmental changes

Geoengineering proposals

• Involve deliberate large-scale interventions in Earth's climate system to mitigate global warming
• Controversial due to potential unintended consequences and ethical considerations
• Major categories of geoengineering proposals:
  • Solar radiation management: reflecting sunlight to reduce global temperatures
    • Stratospheric aerosol injection
    • Marine cloud brightening
  • Carbon dioxide removal: actively removing CO2 from the atmosphere
    • Enhanced weathering of silicate rocks
    • Ocean iron fertilization
    • Direct air capture and storage
• Geochemical considerations in geoengineering:
  • Impacts on global biogeochemical cycles (carbon, nitrogen, sulfur)
  • Potential side effects on ocean chemistry and marine ecosystems
  • Long-term fate and storage of captured carbon dioxide

Planetary habitability

• Explores the conditions necessary for life to exist and thrive on Earth and other planets
• Integrates knowledge from geochemistry, astronomy, and biology
• Key factors influencing planetary habitability:
  • Presence of liquid water
  • Energy sources (solar radiation, geothermal heat)
  • Essential elements for life (C, H, O, N, P, S)
  • Protective magnetic field and atmosphere
• Geochemical approaches to studying planetary habitability:
  • Analysis of meteorites and lunar samples for insights into early Solar System conditions
  • Remote sensing of exoplanet atmospheres for biosignatures
  • Study of extreme environments on Earth as analogs for other planets
• Implications for the search for life beyond Earth and the long-term future of life on our planet