EARTHS HISTORY CH 14 2 Earths age 4

EARTH’S HISTORY CH 14. 2 - Earth’s age – 4. 6 billion years - Determined by geology and radioactive dating of materials

Dating Isotopes- atoms of same element with different # neutrons

- Radioactive isotopes decay – unstable nuclei release particles or radiant energy - Half–life – length of time for ½ sample size to decay

• Compare amount of radioactive isotope to a constant –Ex: Carbon 14 • Carbon 14 declines with respect to Carbon 12 • After 5715 years half Carbon 14 in a sample will have decayed (half-life) • Date objects to ~50, 000 yrs

Origin of 1 st organic compounds • 3 Hypotheses 1. Extraterrestrial Organic molecules carried to Earth on Meteorite

2. Creation –Life put on Earth by divine forces Common to many religions

3. Origin from non-living matter –Miller/Urey experiment (1953)

–Where? » Atmosphere? » Lakes and seas? » Deep sea hydrothermal vents?

1 ST Cells Anaerobic – did not require O 2 Prokaryotic – small, no nucleus Heterotrophic – “fed” on organic molecules from env. Competition for food leads to evolution

nd 2 Cells Autotrophic – made own food – Chemosynthetic – energy from oxidation of inorganic substances – Archaebacteria

rd 3 Photosynthetic Cells – sunlight for energy Byproduct was oxygen – created ozone layer over a billion yrs (protects DNA from UV rays)

th 4 Cells Eukaryotic – Evolved through endosymbiosis –A small aerobic prokaryote entered larger anaerobic prokaryote –Aerobic prok. gave rise to mitochondria (site of aerobic respiration) 2 nd photosynthetic prok. entered & gave rise to chloroplast