Chapter 26 – Early Earth and the Origin of Life

History of Earth on a clock…

1

2 3

4

Billion Years Ago

Origin of Earth (4.5 BYA)

- Earth Cools(3.9 BYA)

Origin of life (3.8 BYA)

Origin of Prokaryotes (3.5 BYA)

Oxygen in atmosphere (2.7 BYA)Endosymbiosis creates eukaryotic life (2.1 BYA)

Multicellular eukaryotic life begins in the sea (1.2 BYA)

Marine invertebrates evolve (.54 BYA)

Colonization of Land (.5 BYA)

Dinosaurs (.1 BYA) Humans (Today)

Origin of Earth

• 4.5 BYA, earth bombarded by rocks intense heat, no water (evaporated)

• Primordial atmosphere form due to volcanic activity– Gases released

• CO, CO2, H2, N2, S, HCL

• No O2

No oxygen = “reducing” power To create organic molecules

(Spontaneous Synthesis)

Back to clock

Primordial Seas

• Earth cools, crust solidifies

• Water is no longer vaporized, and seas form

Back to clock

Origin of LifeDue to non-oxygenated, reducing atmosphere and energy from lightening, heat, UV rays

small monomers (AA, nucleotides, etc.) randomly assemble (kinetics)

Polymerization occurs, forming macromolecules- RNA = 1st hereditary material

(single stranded)- RNA serves as 1st enzymes- Protobionts (membrane droplets) randomly packages organic

molecules inside (precursor to cells)

• Natural selection of protobionts favored those with primitive metabolism and inheritance

• DNA (double stranded) replaces RNA as hereditary material– DNA more stable– RNA take on more modern roles (translation)

Origin of Life

Back to clock

Origin of Prokaryotes

• 3.5 BYA

• 1st prokaryotes were – anaerobic (no O2) in atmosphere, and

– heterotrophic (abundant organic material to be used as food)

Back to clock

Oxygen in Atmosphere (2.7

BYA)• Mutation

heterotrophs gained ability to photosynthesize

• Oxygen gas generated, ends reducing power of atmosphere

• Ends of Spontaneous Generation Phase

Back to clock

Endosymbiosis Creates Eukaryotic Life

• Mutual symbiosis develop amongst autotrophic and heterotrophic prokaryotes

• Endocytosis of symbiotic prokaryotes occur

• Infolding of plasma membrane creates other membrane-bound organelles

Endosymbiosis Creates Eukaryotic Life

Chloroplasts and Mitochondria Support Endosymbiotic Theory because they

- have their own DNA and ribosomes

- are similar in size to prokaryotes

- self-replicate within eukaryotic cells by binary fission

- made up of double membranes, similar in structure to prokaryotes

Back to clock

Last 1.2 Billion Years

Multicellular life in oceans (1.2 BYA)

Colonization of Land (.5 BYA)

Dinosaurs (.1 BYA)

Humans Today