The Origins of Living Systems

*Enduring understanding 1.D: The origin of living systems is explained by natural processes.

-Essential knowledge 1.D.1: There are several hypotheses about the natural origin of life on Earth, each with supporting scientific evidence.

• a. Scientific evidence supports various models. Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. Primitive Earth provided inorganic precursors from which organic molecules could have been synthesized due to the presence of available free energy and the absence of a significant quantity of oxygen.
  • 2. In turn, these molecules served as monomers or building blocks for the formation of more complex molecules, including amino acids and nucleotides.
  • 3. The joining of these monomers produced polymers with the ability to replicate, store and transfer information.
  • 4. These complex reaction sets could have occurred in solution (organic soup model) or as reactions on solid reactive surfaces.
  • 5. The RNA World hypothesis proposes that RNA could have been the earliest genetic material.
    • Learning Objectives:
      • LO 1.27: The student is able to describe a scientific hypothesis about the origin of life on Earth.
      • LO 1.28: The student is able to evaluate scientific questions based on hypotheses about the origin of life on Earth.
      • LO 1.29: The student is able to describe the reasons for revisions of scientific hypotheses of the origin of life on Earth.
      • LO 1.30: The student is able to evaluate scientific hypotheses about the origin of life on Earth.
      • LO 1.31: The student is able to evaluate the accuracy and legitimacy of data to answer scientific questions about the origin of life on Earth.

-Essential knowledge 1.D.2: Scientific evidence from many different disciplines supports models of the origin of life.

• a. Geological evidence provides support for models of the origin of life on Earth. Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. The Earth formed approximately 4.6 billion years ago, and the environment was too hostile for life until 3.9 bya, while the earliest fossil evidence for life dates to 3.5 bya. Taken together, this evidence provides a plausible range of dates when the origin of life could have occurred.
  • 2. Chemcial experiments have shown that is is possible to form complex organic molecules from inorganic molecules in the absence of life.
• b. Molecular and genetic evidence from extant and extinct organisms indicates that all organisms on Earth share a common ancestral origin of life. Evidence of student learning is a demonstrated understanding of each of the following:
  • 1. Scientific evidence includes molecular building blocks that are common to all life forms.
  • 2. Scientific evidence includes a common genetic code.
    • Learning Objectives:
      • LO 1.32: The student is able to justify the selection of geographical, physical, and chemical data that reveal early Earth conditions.