Lecture 3- sljde 27

Phylogeny of Eukarya

  • Overview of the phylogenetic tree of eukaryotes.

    • Human classification within the eukaryotic tree.

    • Eukaryote branch includes organisms like animals and plants.

    • Significant branches include:

      • Apotheia (refers to early forms or lineages).

      • Kingdom Animalia (Animals).

      • Other subdivisions: Biteria, Deuterosomes.

Historical Context of Earth

  • Age of Earth: Approximately 4.6 billion years old.

    • Estimating time:

      • Example exercise counting to four billion sequentially.

      • Provides perspective on the vastness of geologic time.

  • Missing geological records:

    • Oldest rocks are approximately 4 billion years old, indicating missing history due to geological processes.

  • Meteorite dating as a basis for Earth's age:

    • Radioactive dating of meteorites yields an age similar to Earth.

Evolution and the Development of Life

  • Original Earth atmosphere:

    • Believed to be a reducing atmosphere:

    • Main components included:

      • Hydrogen sulfide, ammonia, methane, etc.

    • Contrast with today's oxidizing atmosphere which has 21% oxygen.

  • Importance of ozone layer:

    • Ozone layer (O3) protects Earth from harmful ultraviolet radiation.

The Miller-Urey Experiment (1953

  • Conducted by Stanley Miller and Harold Urey.

  • Aim: To simulate the conditions of early Earth and test the chemical origins of life.

  • Method: Created a mixture of gases (methane, ammonia, hydrogen, water vapor) and stimulated lightning.

  • Result: Formation of amino acids, building blocks of proteins, demonstrating that organic compounds could be synthesized under prebiotic conditions.

  • Further implications of the Miller-Urey Experiment:

    • Demonstrated the possibility of abiogenesis, where life arises from non-living matter.

    • Suggested pathways for the development of more complex organic molecules.

  • Evolution of Prokaryotic Cells:

    • First forms of life on Earth were prokaryotic, which include bacteria and archaea.

    • Key characteristics:

    • Lack of nucleus and membrane-bound organelles.

    • Reproduce asexually via binary fission.

  • Endosymbiotic Theory:

    • Proposed by Lynn Margulis.

    • Explains the origin of eukaryotic cells from prokaryotic cells through symbiosis.

    • Evidence includes:

    • Mitochondria and chloroplasts have their own DNA similar to bacterial DNA.

    • Double membranes present in these organelles.

  • Evolution of Multicellular Life:

    • Multicellularity allowed for specialization of cells and complexity in organisms.

    • Examples include:

    • Fungi, plants, and animal kingdoms developed from single-celled ancestors.

  • Cambrian Explosion:

    • Occurred approximately 541 million years ago.

    • Represents a significant evolutionary event where most major animal phyla appeared in the fossil record.

  • Mass Extinctions:

    • Five major mass extinction events have reshaped life on Earth.

    • Resulted in the loss of biodiversity but also provided opportunities for the evolution of new species.