Charlespogi

• The Earth is about 4.6 billion years old (time of the first likely solid surface)
• Radioisotope dating


  Method used to determine the age of the Earth
• Evidence for the age of the Earth


  • Oldest known Earth minerals (4.4 billion years ago)
  • Oldest known rocks on Earth (4.1 billion years ago)
  • Oldest known meteorites (4.6 billion years ago; for the age of the solar system)
• Components of the early Earth's atmosphere (when life first appears in the fossil record)


  • CO2
  • H2O
  • CO
  • H2
  • N2
  • Small amounts of NH3, H2S, and CH4
• The early Earth's atmosphere lacked free oxygen
• Abundant energy sources on the early Earth

  • Volcanism
  • Thunderstorms
  • Bombardment with particles and radiation from space
• The early Earth had more UV radiation than today
• Four requirements for the current model of chemical evolution of life on the early Earth

  • Little or no free oxygen
  • Abundant energy sources
  • Chemical building blocks (water, dissolved mineral ions, atmospheric gases)
  • Time (plenty before the first traces of life from 3.8 billion years ago)
• Spontaneous Generation (Abiogenesis)


  The hypothesis that life arises regularly from non-living things
• Francesco Redi (1668) demonstrated that maggots were the offspring of flies, not products of spontaneous generation
• Louis Pasteur (1859) showed that microorganisms do not arise from meat broth

  
• Miller/Urey Experiment (1953)


  Simulated the conditions of Earth's early atmosphere and oceans, adding energy to simulate lightning, and produced organic compounds including amino acids
• Primordial Soup Hypothesis


  Proposed by Alexander Oparin that life on Earth developed through gradual chemical changes of organic molecules in the "primordial soup" on early Earth
• Exogenesis


  The hypothesis that primitive life may have originally formed extraterrestrially either in space or on a nearby planet such as Mars
• Protobionts


  The simple cell that is the precursor to life, resembling microspheres composed of inorganic and organic molecules trapped inside a lipid bilayer membrane
• RNA world hypothesis


  RNA can catalyze reactions and store genetic information, and in vitro evolution of RNA has shown this is feasible
• DNA likely came later and had the selective advantage of greater stability
• Microfossils


  The first evidence of life in the fossil record, isotopic carbon "fingerprints" in rocks from ~3.8 billion years ago
• Stromatolites


  Rocklike structures made up of layers of bacteria and sediment, containing the first evidence of cells as microfossils of prokaryotic cells dated to ~3.5 billion years ago
• The first cells were most likely anaerobic heterotrophs, as there was likely an abundance of organic molecules available for food early on
• The first photosynthetic organisms were likely the purple and green sulfur bacteria, which use H2S as a hydrogen donor
• Banded iron formations


  Indicate the massive release of oxygen into the oceans around 2.5 billion years ago
• By 2 billion years ago, oxygen levels began to build up in the atmosphere, which had a profound impact on life on Earth
• The formation of the ozone layer soon after oxygenation of the atmosphere provided protection from UV radiation and allowed life to expand to regions at and near the Earth's surface
• Eukaryotic cells first appear in the fossil record about 2 billion years ago, long after prokaryotic cells
• DNA sequencing provides evidence of common ancestry of all life on Earth, with eukaryotes splitting from Archaea about 2 billion years ago
• Paleontology


  The scientific study of the existence of life, including the origin and eventual destruction or extinction of different groups of organisms, through careful observation and documentation of fossils
• Paleontologists


  Scientists who specialize in studying the ecologies of the past and the evolution of organisms that thrived in these ecologies
• Geology


  The study of the different materials that make up Earth, to understand the history of Earth by focusing on changes in climate and land formation over time
• Geologists


  Scientists who carefully study rock formations and fossils to measure different physical properties of Earth
• Paleontologists look at fossil remains to study primitive life, while geologists study the outer layer of Earth's crust to understand Earth's history
• Levels in the Geologic Time Scale

  • Eons
  • Eras
  • Periods
  • Epochs
• Eons in the Geologic Time Scale

  • Hadean
  • Archaeozoic
  • Proterozoic
  • Phanerozoic
• Hadean Eon


  From 4.6 to 3.9 billion years ago, characterized by Earth's formation from dust and gases
• Archaeozoic Eon


  From 3.9 to 2.5 billion years ago, where the first life-forms represented by single-celled organisms appeared
• Proterozoic Eon


  From 2.5 billion years ago to 540 million years ago, where the first multicellular organisms arose and mass extinctions occurred
• Phanerozoic Eon


  The most recent eon, beginning more than 500 million years ago, characterized by the existence of organisms with skeletons or hard shells
• Eras in the Phanerozoic Eon

  • Pre-Cambrian
  • Paleozoic
  • Mesozoic
  • Cenozoic
• Paleozoic Era


  Began about 540 million years ago and lasted for about 300 million years, marked by a rich fossil record of many marine organisms and the start of Pangea formation
• Mesozoic Era


  Began about 200 million years ago and lasted for about 180 million years, also called the Age of Dinosaurs and the Age of Reptiles, also marked by the appearance of flowering plants