Early Life - Proterozoic Eon Notes

EARLY LIFE

• Proterozoic Eon: History of Earth through Deep Time

WHAT IS LIFE?

• Biologists define life using criteria such as metabolism (chemical activity for self-maintenance) and reproduction.
• The distinction between life and non-life is complex (e.g., viruses, microspheres/protocells).
• Viruses and/or microspheres might have been involved in the origin of life.

ORIGIN OF LIFE

• The early Earth's atmosphere contained $CO<em>2$, $H</em>2O$, $N<em>2$, along with $NH</em>3$ and $CH_4$.
• Lightning and ultraviolet radiation could have provided energy to convert atmospheric chemicals into organic monomers (molecules reacting to form polymers).
• Monomers, such as amino acids, are the building blocks of life.

EXPERIMENTS

• Stanley Miller and Harold Urey (1950s) simulated early Earth's atmosphere in vitro to explore the origin of life.
• They combined water, methane, ammonia, and hydrogen in a flask connected to a smaller flask of water.
• Water was heated to produce vapor, which entered the chemical flask, and electrical sparks simulated lightning between the containers.
• The vapor was cooled, collected, and analyzed.
• Five amino acids were identified initially. Reanalysis revealed greater than 20 amino acids.

EXPERIMENTS (CONTINUED)

• Additional experiments using different gases synthesized many of the 20 amino acids found in organisms.
• Monomers can polymerize into polymers, including thermal proteins or proteinoids.
• In aqueous solutions, they form microspheres with life-like characteristics: outer wall, osmotic swelling/shrinking, budding, binary fission, and streaming movement of inner particles.

RNA AND DNA

• All known life contains polymeric nucleic acids DNA and RNA.
• These molecules create, encode, store, transmit, and express information; essential for reproduction and evolution.
• The exact development of RNA and DNA is not known.
• Scientists agree on the basic requirements for the origin of life, but debate the exact steps and significance of experimental results.

RNA WORLD

• Before DNA genomes and protein enzymes, RNA may have served as both genetic material and catalyst.
• Joyce (2002) proposed simpler lifeforms using RNA for genetic storage and catalysis.

EARLY LIFE

• Earliest known life was prokaryotic (no nucleus or membrane-bound organelles): Bacteria and Archaea.
• Archaea can thrive in very hot, acidic, and saline environments.

HYDROTHERMAL VENTS

• Submarine hydrothermal vents precipitate copper, zinc, and iron minerals.
• These vents may have produced the first self-replicating molecules.
• Vents contain C, N, S, P, and other elements necessary for life, along with a hydrothermal energy source.
• Polymerization could have occurred on the surfaces of clay minerals.
• Some amino acids have been detected in vent emissions.
• Hydrothermal vents are a favored site for the origin of life, but other geological settings and extraterrestrial origins are also proposed.

EARLIEST FOSSILS

• Earliest fossils are controversial; distinguishing single cells from mineral grains is difficult.
• Stromatolites are some of the oldest known fossils.
• Microbial mats trap layers of sediment via sticky microorganisms.
• Stromatolites can be confused with sedimentary structures.

LACA

• Origins of life: <4.3 Ga
• LUCA (Last Universal Common Ancestor)
• LBCA (Last Bacterial Common Ancestor)
• FECA (Last Eukaryotic Common Ancestor): >1.65 Ga
• LECA (Last Eukaryotic Common Ancestor)
• Methanogenesis: >2.77 Ga
• Photosynthesis: >3.42 Ga
• Stromatolite: >3.42 Ga
• Microfossil: >3.22 Ga
• Cyanobacteria: >1.88 Ga
• Protist: >1.65 Ga
• Algae: >1.05 Ga

PROTEROZOIC EON

• Precambrian: 4600 to 542.0 mya
• Archean: 4000 to 2500 mya
  • Neoarchean: 2800 to 2500 mya
  • Mesoarchean: 3200 to 2800 mya
  • Paleoarchean: 3600 to 3200 mya
  • Eoarchean: 4000 to 3600 mya
• Proterozoic: 2500 to 542.0 mya
  • Paleoproterozoic: 2500 to 1600 mya
  • Mesoproterozoic: 1600 to 1000 mya
  • Neoproterozoic: 1000 to 542.0 mya
• Hadean: 4600 to 4000 mya
• Key aspects of the Proterozoic Eon include tectonics, orogenies, supercontinents, atmosphere, glaciation, and mineral resources.

PROTEROZOIC

• 2.5 Ga - 542 Ma (~42% of total Earth history)
• Subdivisions: Neoproterozoic, Mesoproterozoic, Paleoproterozoic
• Late Proterozoic: 650 Ma

SUPERCONTINENTS

PALEOPROTEROZOIC

• Rise in atmospheric $O_2$ (Great Oxidation Event).
• Tectonically active: mountain-building on all continents.
• First major ice age.
• Single-celled life.

Atmospheric Oxygen Levels

• Trends in atmospheric oxygen levels over time, relative to present atmospheric level (PAL).
• Diagrammatic representation of oxygen levels and their relationship to continental processes.

Oxygenation and Early Life

• A graphical representation depicting oxygen levels in relation to geological periods and the diversification of life, including bacteria, archaea, and eucarya. The graph spans from the Archean to the Neoproterozoic, marked by significant events like the Great Oxidation Event (GOE).
• Key: F - Fossil evidence, I - Isotopic evidence, B - Biomarker evidence.

LAURENTIA

• Land masses sutured together ~1.7 Ga to form the North American craton.
• Characterized by intense folding, metamorphism, and volcanism.
• Shallow epicontinental (epicratonic) seas flooded continental interiors.