THE EARLY EARTH AND THE EMERGENCE OF LIFE

• The planet Earth formed about 4.6 billion years ago (BYA) based on evidence from radiometric dating of meteorite materiaL
• Prokaryotes were Earth’s first organisms.
• Eukaryotes’ first appearance on Earth is about 1.8 BYA.
• FOUR MAIN STAGES OF CHEMICAL AND PHYSICAL PROCESSES ON EARLY EARTH

  1. The abiotic (nonliving) synthesis of small organic molecules, such as amino acids and nitrogenous bases.
  2. Joining of these small molecules into macromolecules, such as proteins and nucleic acids.
  3. The packaging of these molecules into protocells.
  4. The origin of self-replicating molecules that eventually made inheritance possible.
• Synthesis of Organic Compounds on Early Earth

  ● Miller-Urey Experiment provided the first evidence that organic molecules needed for life could be formed from inorganic components
• ● Second source of organic molecules may have been meteorites
• Meteorite was also found to have included simple sugars, and nitrogenous bases like uracil.
• Protocells: 1. Protocells likely originated with self-replicating molecules and a metabolism-like source in early Earth.
• Protocells: 2. Vesicles, fluid-filled compartments enclosed by membranes, played a crucial role in the existence of protocells.
• Protocells: 3. Abiotically produced vesicles displayed key characteristics such as simple reproduction, metabolism, and maintenance of internal chemical environments.
• Self-Replicating RNA

  ● RNA catalysts are called ribozymes.
• Self-Replicating RNA: 2. Some ribozymes can make complementary copies of short pieces of RNA (if they are supplied with nucleotide building blocks)
• Self-Replicating RNA: 3. Vesicles with self-replicating RNA would be unique and could grow, split, and pass RNA to daughter vesicles
• Self-Replicating RNA: 4. Early Earth may have had an "RNA world" where small RNA molecules replicated and stored genetic information.
• Self-Replicating DNA: 5. DNA is chemically more stable than RNA and can be replicated more accurately.
• The geologic record of Earth's history is divided into three eons: Archaean, Proterozoic, and Phanerozoic.
• Stromatolites are layered rocks formed by certain prokaryotes.
• Stromatolites are major constituents of the fossil record.
• Prokaryotes were Earth's sole inhabitants from about 3.5 billion years ago to 2.1 BYA, transforming life through photosynthesis, which produced atmospheric oxygen
• Cyanobacteria played a major role in releasing oxygen into the atmosphere.
• Atmospheric oxygen levels gradually increased between 2.7 to 2.3 BYA, with a rapid increase hypothesized to be caused by the emergence of eukaryotic cells containing chloroplasts.
• Eukaryotic cells are believed to have evolved from prokaryotic cells through the endosymbiotic theory.
• The Endosymbiotic Theory - suggests that mitochondria and chloroplasts were once independent prokaryotes that began living within larger host cells
• The Endosymbiotic Theory - Initially, this relationship was likely parasitic, with the host cell feeding on other organisms through phagocytosis.
• Mitochondria was formed through bacteria capable of aerobic respiration.
• Chloroplasts originated from photosynthetic bacteria.
• Evidence supporting the endosymbiotic origin of mitochondria and plastids are:

  ○ Similarities in membrane structure

  ○ Replication process

  ○ DNA structure

  ○ Protein synthesis machinery to living prokaryotes
• Mitochondria and plastids both have:

  ○ Single, circular DNA molecules similar to bacterial chromosomes

  ○ Ribosomes resembling prokaryotic ribosomes
• Such ribosomes resemble prokaryotic ribosomes in terms of:

  ○ Size

  ○ RNA sequence

  ○ Sensitivity to certain antibiotics.
• Which of the following is NOT a characteristic of the early earth right after its formation?

  a.Bombarded with huge chunk of rock and ice

  b. The water available was vaporized

  c. Eukaryotes inhabit the planet

  d. There is an extreme heat throughout the planet
• When did the massive bombardment on earth ended?

  a.4 million years ago

  b. 40 million years ago

  c. 4 billion years ago

  d. 40 billion years ago
• Who are the two people who hypothesized that that life arose gradually from inorganic molecules?

  • Alexander Oparin and Haldane
• When organic molecules coming from inorganic molecules were hypothesized, what were the source of energy scientists thought of?

  • Lightning and UV radiation
• What is the correct order of the eons in Earth’s history?

  • Archaean, Proterozoic, Phanerozoic
• Stromatolites are layered rocks formed by certain prokaryotes.
• Stromatolites are majorconstituents of the fossil record.
• Prokaryotes were Earth's sole

  inhabitants from about 3.5 billion

  years ago to 2.1 BYA, transforming

  life through photosynthesis, which

  produced atmospheric oxygen.
• Cyanobacteria played a major role

  in releasing oxygen into the

  atmosphere.
• Eukaryotic cells are believed to

  have evolved from prokaryotic cells

  through the endosymbiotic theory.
• endosymbiotic theory suggests that mitochondria and

  chloroplasts were once

  independent prokaryotes that

  began living within larger host cells.