Geol LE 2

• Change


  Inevitable, caused by environmental changes and the fact that nothing is permanent except change
• Man


  A recent agent of change
• Major Concepts


  • Time
  • Fossils & Rock Records
  • Life Domains
• Geologic Time


  • Concept of time is one of the major contributions of geosciences to knowledge
  • Time is immense (Earth is 4.56 billion years old)
  • Rate of changes: slow -> fast
• Earth came from dust-cloud or nebula derived from a supernova
• "You were at least once a star"
• Rates of changes


  Man's appearance: 2 - 2.5 Ma = 0.04% of geologic time
• Records of Earth History

  • Fossils
  • Earth Materials
  • Rock & Mineral Deposits
  • Structures and features in them
• Fossils


  Actual remains, imprints, and traces of formerly living organisms older than 11,000 years
• Types of Fossils


  • Actual remains (fossils)
  • Casts, molds
  • Trace fossils: manifestation of activity (burrows, coprolites, tracks)
  • Chemicals: molecules
• Actual Preservation


  • Amber
  • Tar Pits
  • Ice
• Ichnofossils/Trace Fossils


  Traces/tracks of animals
• Living Fossils


  An organism that has remained essentially unchanged from earlier geologic times and whose close relatives are usually extinct
• Living Fossils


  • Ginkgo biloba
  • Coelacanth (Latimeria chalumnae)
  • Horseshoe Crab
• The fossil record is incomplete but pattern recognition is still possible
• Evolution of the horse, showing reconstruction of the fossil species obtained from successive rock strata
• Major Domains of Life

  • Eubacteria
  • Archaea
  • Eucarya
• Eubacteria


  • Prokaryote: lacks a nuclear membrane
  • Some are considered ancestors of Archaea
  • Lack a nuclear membrane and are unicellular
  • Cell walls exhibit differences from those of Archaea and Eucarya
  • Capable of chlorophyll-based photosynthesis, although many can function anaerobically
  • A large number of heterotrophs oxidize organic molecules for energy; some utilize inorganic reactions to produce organic molecules
  • Some species thrive in high temperatures and may be ancestral to Archaea
  • Examples include Streptococcus pneumoniae and cyanobacteria (blue-green algae)
• Archaea


  • Prokaryote: lacks a nuclear membrane
  • Non-pathogenic
  • Probably share a common ancestor with Eucarya
  • Many obtain energy from inorganic reactions to synthesize organic matter
  • Typically found in extreme environments characterized by high temperature, high salinity, and anaerobic conditions
  • Example: Pyrolobus fumarii, which is found in hydrothermal vents and hot springs, capable of growth up to 113ºC
• Eucarya

  • Possess a nuclear membrane (eukaryote)
  • Contains many types of membranous organelles within the cell
  • Chloroplasts likely originated from cyanobacteria through endosymbiosis
  • Mitochondria likely originated from aerobic bacteria through endosymbiosis
  • Developed complex cells through symbiotic relationships with other organisms
  • Examples include protists, fungi, plants, and animals
• The origin of eukaryotic cells is thought to have occurred through a process known as endosymbiosis, which is a key aspect of the endosymbiotic theory
• Early heterotrophs and autotrophs were initially unicellular prokaryotes
• According to the endosymbiotic theory, free-living prokaryotic bacteria established a relationship with another primitive cell type containing a nuclear membrane
• The endosymbiotic theory suggests that eukaryotic cells evolved from symbiotic relationships between different types of prokaryotic cells
• Smaller prokaryotes, such as bacteria, were engulfed by larger prokaryotes, benefiting both parties. Over millions of years, these smaller cells evolved into organelles like mitochondria (from aerobic bacteria) and chloroplasts (from cyanobacteria) within eukaryotic cells, leading to the development of more complex multicellular organisms
• Cryptozoic/Precambrian (4.6 Ga - 540 Ma) or The Eon of Hidden Life


  • Represents approximately 90% of Earth's history
  • Records are much more obscure compared to the Phanerozoic eon
• Cryptozoic Climate


  Not significantly different from the Phanerozoic, except for some distinctive features: Acid rain, likely due to atmospheric pollutants; Warmer global temperatures caused by the greenhouse effect from increased carbon dioxide levels
• Evidence suggests periods of extremes such as glaciation (ice ages) and aridity (dry conditions) during the Cryptozoic
• Hadean Eon (4.56 - 3.8 billion years ago)


  • Characterized by meteorite bombardment and intense impacts on Earth's surface
  • Witnessed the formation of a second atmosphere and the development of oceans, marking crucial environmental changes
  • Formation of the oldest known crustal rocks dating back to 3.9 - 4.2 billion years ago, providing insights into early planetary geology
  • Towards the end of the eon, the origin of life is hypothesized to have occurred, potentially through processes like abiogenesis (spontaneous generation of life from non-living matter)
  • The concept of panspermia is considered, suggesting that life could have been seeded on Earth by cosmic sources such as meteoroids or comets during this period
• Archaean Eon (3.8 - 2.5 billion years ago)


  • Dominated by anaerobic (lacking oxygen) conditions
  • Transitioned to slightly aerobic conditions around 3 billion years ago
  • Hosted the earliest life forms, primarily prokaryotes (single-celled organisms lacking a nucleus)
  • The first life forms may have emerged around mid-ocean ridges during this eon
• Key Events in the Archaean Eon (3.8 - 2.5 billion years ago)


  • Formation of kerogen around 3.8 billion years ago in Greenland, suggesting the activity of photosynthetic organisms that altered the carbon reservoir
  • Possible appearance of the first life forms between 4.1 to 3.8 billion years ago
  • Discovery of rod and spherical shaped structures interpreted as remains of bacterial and blue-green algae, indicating the presence of ancient microbial life during this period
• Researchers have identified fossilized evidence of bacteria from ancient seafloor hydrothermal vent precipitates in the Nuvvuagittuq belt in Quebec, Canada, dating back at least 3.77 billion years (and possibly as old as 4.28 billion years). These findings suggest that these fossils represent the oldest indication of life discovered on Earth to date
• Stromatolites


  • Layered structures produced by the activity of cyanobacteria
  • Composed primarily of calcium carbonate (CaCO3)
  • Fossilized examples date back as old as 3.5 billion years
  • Modern stromatolites can still be found today, such as in Shark Bay, Australia, demonstrating the ongoing presence of these structures produced by cyanobacteria
• Archaean Life Characteristics


  • Rarity of fossils attributed to either low diversity or preservation bias
  • Dominance of prokaryotes, considered descendants of the earliest organisms on Earth
  • Life predominantly anaerobic during this period
  • Remarkable stability in life forms, showing no visible signs of change for approximately 1.5 billion years
  • Appearance of multicellular organisms occurred relatively late, around 0.7 billion years ago; prior to this, life was primarily unicellular bacteria
• The Proterozoic Eon (2.5 billion years ago - 540 million years ago)


  • Prokaryotic cyanobacteria played a crucial role by producing oxygen (O2), leading to a gradual increase in atmospheric oxygen levels
  • However, the released oxygen reacted with dissolved iron in water, forming banded iron formations (BIF) as evidenced in geological records
  • By approximately 1.1 billion years ago, the Earth had a single supercontinent known as Rodinia, representing a significant geological event during the Proterozoic eon
• Gunflint Fossils


  • Discovered in Canada dating back to approximately 1.9 billion years ago
  • Fossils include threads (potentially cyanobacteria), spherical bodies, and structures resembling star-, umbrella-, and parachute-shaped bodies
  • Some of these fossilized forms bear resemblance to modern manganese bacteria found in recent lake environments
• First Eukaryotic Cells (1.8 billion years ago)


  Marks the emergence of the first eukaryotic cells during the Proterozoic eon
• First Appearance of Multicellular Eukaryote


  • Characterized by the presence of carbonaceous sheets and ribbons
  • These structures became more abundant from around 1.3 billion years ago and onwards, indicating the early evolution and diversification of multicellular eukaryotes during the Proterozoic eon
• Varangian Glaciation


  • Occurred at the end of the Proterozoic eon
  • Involved the presence of continental glaciers at nearly equatorial latitudes, a phenomenon known as "snowball Earth"
  • The cause of this glaciation is controversial, but it resulted in Earth resembling a lifeless frozen world, possibly similar to Mars
  • Following the retreat of the glaciers, the emergence of multicellular life occurred after approximately 3 billion years of single-celled life, representing a significant evolutionary transition
• Late Proterozoic Period


  • Free iron (Fe) was used up, leading to the buildup of free oxygen (O2) in oceans and the atmosphere
  • Prokaryotes either died off or retreated to oxygen-free environments, such as within animal guts
  • Eukaryotes emerged during this period and developed mechanisms to tolerate and utilize oxygen, adapting to the increasing oxygen levels in the environment