Chapter 26Early Earth and the Origin of LifeImpact changing lifeLife changes planetHistory and life inseparable

History of the World part I.

Figure 26.1 Some major episodes in the history of life

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.

Figure 26.4 Bacterial mats and stromatolites

Fossilized Cyanobacteria

Eukaryotic cells first found were 1.7 billion years old.ChloroplastsMitochondrionCellular RespirationMulticellular evolved 1.2 bill yrs. agoCell division, cell differentiationLimited through early Precambrian age due to ice ageSnowball earth hypothesis: life confined to deep thermal vents

Figure 26.6 Fossilized alga about 1.2 billion years old

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.

Figure 26.8 The Cambrian radiation of animals

Origin of lifeSpontaneous generation: Life emerged from the inanimate.

Pasteurs Experiments: formed Bio-genisis theory, Life from life.Four Stage hypothesis for Life FormationAbiotic (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-AssemblyOparin/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.

Figure 26.10 The Miller-Urey experiment

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

Figure 26.11 Abiotic replication of RNA

Self Assembly of ProtobiontsForm spontaneously, liposomes for basic bilayerSelectively permeable.Membrane potential as energy, discharge as electrical impulse.Reproduce, simple metabolism

Figure 26.12 Laboratory versions of protobionts

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

Figure 26.13 Hypothesis for the beginnings of molecular cooperation

Major Lineages of LifeTwo fundamental differences:ProkaryotesEukaryotes

Figure 26.15 Whittakers five-kingdom system

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. Plantae4. Fungi5. Animalia

Figure 26.16 Our changing view of biological diversity

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) ArchaezoaProtistaChromistaPlantaeFungiAnimalia

Classification Cont.1.Domain Bacteria2.Domain Archaea3.Domain Eukarya (Eukaryotes)1. Archaezoa2. Euglinozoa3. Alveolata4. Stramenopila5. Rhodophyta6. Plantae7. Fungi8. AnimaliaA Three-domain System