Quaternary glaciation

(noun)

Related Terms

Examples of Quaternary glaciation in the following topics:

  • Early Lifestyles

    • However, the traditional theory has been that these early migrants moved into the Beringia land bridge between eastern Siberia and present-day Alaska around 40,000–17,000 years ago, when sea levels were significantly lowered due to the Quaternary glaciation. 
    • As the Quaternary extinction event was happening, the early inhabitants of the Americas began to rely more on other means of subsistence.

  • Shifts Occurring by Addition-Elimination Mechanisms.

    • A nitrogen ylide, formed by reaction of a quaternary ammonium salt with strong base, is the reactive intermediate.

  • Protein Structure

    • To determine how the protein gets its final shape or conformation, we need to understand these four levels of protein structure: primary, secondary, tertiary, and quaternary.
    • The quaternary structure of a protein is how its subunits are oriented and arranged with respect to one another.
    • As a result, quaternary structure only applies to multi-subunit proteins; that is, proteins made from one than one polypeptide chain.
    • Proteins made from a single polypeptide will not have a quaternary structure.

  • Secondary & Tertiary Structure of Large Peptides and Proteins

    • Mellitin, from honey bee venom, has a well-defined quaternary structure, half of which is shown here.
    • Collagen is a widely distributed fibrous protein with a large and complex quaternary structure.
    • The supramolecular assembly of four subunits exemplifies a quaternary structure.
    • Such multiple-subunit proteins possess a quaternary structure, in addition to the tertiary structure of the subunits.
    • The four polypeptide chains are bound to each other by salt bridges, forming a tetrameric quaternary structure.

  • Nucleophilicity of Sulfur Compounds

    • Sulfides, for example, react with alkyl halides to give ternary sulfonium salts (equation # 1) in the same manner that 3º-amines are alkylated to quaternary ammonium salts.

  • The Pleistocene Extinction

    • It is well known that the North American, and to some degree Eurasian, megafauna disappeared toward the end of the last glaciation period.

  • Conclusion: Pre-Colonial Development of North America

  • Types of Disinfectants

    • Types of disinfectants include: Air disinfectants, Alcohols, Aldehydes, Oxidizing agents, Phenolics, Quaternary ammonium compounds, Silver, and Copper alloy surfaces.
    • Quaternary ammonium compounds (quats), such as benzalkonium chloride, are a large group of related compounds.

  • Electrophilic Substitution at Nitrogen

    • Even 3º-amines may be alkylated to form quaternary (4º) ammonium salts.
    • In the latter case a quaternary "onium" salt may be formed as an intermediate, but this rapidly breaks down in water to liberate the original 3º-amine (lower right equation).

  • Biodiversity Change through Geological Time

    • The main hypothesis for its cause was a period of glaciation followed by warming.