Origins

                  Miller Experiment 1956

- Miller attempts to replicate (in vitro)  conditions of the Early atmosphere (H₂O NH₃, CH_4, H_2, CO₂)

- heat and high voltage electrical energy was applied to the closed circuit

- in several days water samples revealed amino acids, nucleic acids,  complex molecules common to all life forms

- what does this prove?

Life's progress over time

> 3.6-3.7 billion years ago: appearance of life
> 2.5 billion years ago oxygen-forming photosynthesis
> ~2.2 billion years ago: aerobic respiration
> ~1.5 billion years ago: first evidence of fossil eukaryotes

         Precambrian Era (simple unicellular life, prokaryotes, low diversity,  anaerobic life) 

3.6-3.7 billion years ago: appearance of life anaerobic heterotrophes
> likely first cells were anaerobic, heterotrophic bacteria
anaerobic = does not require free oxygen
heterotrophic = does not make its own food  (primordial broth supplies food)

>  next step: anaerobic autotrophs
Were able to fix CO₂ (take carbon from air)
turning CO2 + H into organic molecules
Hydrogen donors initially were H₂, H₂S

Energy sources for autotrophics >>>>                              Deep Sea Thermal Vent
> First used chemical energy from elements in surrounding medium (primordial broth)
chemoautotrophs  ( we see this in deep-sea vents today!)
> As this energy ran low, evolved ability to capture energy from light
> Photoautotrophs  (primitive photosynthesis)

   Life' s first major environmental crisis  (loss of H+ donors in primordial broth))

Available hydrogen donors (H₂, H₂S) used up quickly  (goodbye primordial broth)
Key innovation around 2.5 billion years
oxygen-forming photosynthesis (cyanobacteria)
Use of H₂O as a hydrogen donor

              Life' s second major environmental crisis                 Iron Banded Rock

Toxic O₂ released into atmosphere
Most of the initial O₂ was locked up by iron in the oceans and soils (Banded iron formations) = rusting of Earth minerals 
More O₂ from water keep coming, leading to an O₂ rich atmosphere

                                      Aerobic respiration
endosymbiotic evolution of mitochondria led to aerobic respiration a highly efficient system
allowed larger cells and the potential of multicellular organisms that establish complex food webs within ecosystems

            Cambrian Era (sudden appearance of vast species diversity , eukaryotes)
- the Cambrian era started about 600 M Y ago dinosaurs died off 65 million years ago
- human culture about 50K Y old
- scientific human culture about 250 Y old

want to know about geochronology visit my Earth Space Site