Chapter 26 Early Earth and the Origin of Life

Chapter 26 Early Earth and the Origin of Life • Impact changing life • Life changes planet • History and life inseparable

History of the World part I.

Introduction to the History of Life • 3.5 and 4.0 billion years ago. Microscopic and unicellular. • Prokaryotic cells 3.5 billion years found in stromatolites. (hydrothermal vents/bacterial mats) • O2 accumulated app. 2.7 bill, years ago, photosynthesis by cyanobacteria, dissolved in water (oceans), marine sediments in form of iron oxide.

FossilizedCyanobacteria

Eukaryotic cells first found were 1.7 billion years old. • Chloroplasts • Mitochondrion • Cellular Respiration • Multicellular evolved 1.2 bill yrs. ago • Cell division, cell differentiation • Limited through early Precambrian age due to ice age • Snowball earth hypothesis: life confined to deep thermal vents

Cambrian Age: great diversity formed major groups • For nearly 90% of its existence, life on Earth was confined to aquatic environments. • Plants and fungi led the way to land about 475 million years ago. • Gradual progression. Plants associated with fungus. • Transformed landscape for herbivores etc.

Origin of life • Spontaneous generation: Life emerged from the inanimate. • Pasteur’s Experiments: formed Bio-genisis theory, Life from life. • Four Stage hypothesis for Life Formation • Abiotic (nonliving): accumulation of small organic molecules, or monomers, such as amino acids and nucleotides. • Joining of these monomers into polymers.(proteins and nucleic acids.) • Formation of self replicating molecules, inheritance possible. • Packing these molecules into “protobionts:

Protobionts can Form by Self-Assembly • Oparin/Haldane theory, Urey/Miller tested • Laboratory experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds. When mixed with cool water, proteinoids self-assemble into tiny droplets called microspheres. • These microspheres are coated with a selectively permeable protein membrane and undergo osmotic swelling or shrinking when placed in solutions of different salt concentration. • The protobionts can discharge a voltage in nerve-like fashions; such excitability is a characteristic of all life. Microspheres are not alive, they only display some of the properties of life.

Produced polymers (proteins, nucleic acids w/o enzymes) • Required hot clay to form.

RNA may have been the first Genetic Material • Molecular Replication: ribozymes as catalyst. • Natural Selection, competition for monomers. • RNA is autocatalytic, capable of ribozyme catalyzed replication • Genotype and phenotype (sequence & conformation)

Self Assembly of Protobionts • Form spontaneously, liposomes for basic bilayer • Selectively permeable. • Membrane potential as energy, discharge as electrical impulse. • Reproduce, simple metabolism

Natural Selection using inheritable information • Most successful would grow and split. • Copies of gene to each (reproduction) • Mutation/variation occurs • Evolution: differential reproductive success. • May have led to DNA becoming inheritable.

Major Lineages of Life • Two fundamental differences: • Prokaryotes • Eukaryotes

The Major Lineages of Life • Linnaeus divided all know forms of life between the plant and animal kingdoms. • A five Kingdom system. • 1. Monera: Prokaryotic cells. • 2. Protista: All eukaryotic cells that did not fit the definition of plant, fungi, or animal. • 3. Plantae • 4. Fungi • 5. Animalia

Classification Cont. • An eight-Kingdom system. Prokaryotes are split in two Kingdoms, Bacteria and Archaea. Also, Protists are split into three Kingdoms, Archaezoa, Protista, and Chromista. • Bacteria (eubacteria) • Archaea (archeabacteria) • Archaezoa • Protista • Chromista • Plantae • Fungi • Animalia

Classification Cont. A Three-domain System 1. Domain Bacteria 2. Domain Archaea 3. Domain Eukarya (Eukaryotes) 1. Archaezoa 2. Euglinozoa 3. Alveolata 4. Stramenopila 5. Rhodophyta 6. Plantae 7. Fungi 8. Animalia

Chapter 26 Early Earth and the Origin of Life