Transcript SO HOW DID LIFE BEGIN ON EARTH??

Early Earth Conditions
Origin of Life Beliefs
• 1. Spontaneous Generation- idea that
nonliving material can produce life
ex. People believed decaying meat
produced maggots
ex. Mice suddenly appearing in sacks of
grain
• 1668- Francesco Redi (Italian physician)
disproved spon. gen.
Redi’s Spontaneous Generation
Experiment
Disproving spontaneous generation
• Redi disproving spon. Gen. allowed
people to believe in biogenesis (idea that
living organisms come from other
living organisms)
• SO HOW DID LIFE BEGIN ON EARTH??
• TO GET LIFE YOU NEED TO FORM
ORGANIC MOLECULES (CONTAIN
CARBON)
Early Earth Conditions
• SO HOT!!! Due to radiation, volcanoes,
friction from colliding meteorites
• All eruptions of volcanoes made all gases
present (CO2, N2, H2, CO, methane, and
ammonia
• H2O is present as water vapor b/c it’s so
hot!!
Early Earth Conditions
• About 3.6 byo (billion years ago) earth
started to cool and H2O condensed to form
liquid H2O
*Rock evidence shows 1st life began then
• Led to millions of years of rainstorms to
form the oceans
• Helps support Miller/Urey experiment
Formation of Organic Molecules
• 1. Believed early atmosphere contained
little free O2
• 2. Most atmosphere was made of (water
vapor, carbon dioxide gas, nitrogen gas,
methane gas, ammonia, hydrogen gas,
and carbon monoxide
• *1938 Alexander Oparin proposed
Primordial Soup Theory (says life began
in the oceans)
Primordial Soup Theory
• Oparin said energy from sun, lightning, &
Earth’s heat triggered chem rxns. to
produce small organic molecules from
substances present in Earth’s atmosphere
• Then rain washed these molecules into
oceans making this primordial soup
• 1953 Stanley Miller/Harold Urey (American
Scientists) wanted to test Oparin’s theory
by simulating Earth’s early conditions in
the lab
Miller/Urey Experiment
• 1. Mix water vapor (steam) w/ ammonia,
methane gas, and hydrogen gas
• 2. Send electric current (simulates lighting)
through it
• 3. Cool gases- which produces a liquid
that simulates rain
• 4. Collect liquid in flask
• 5. Results- found several kinds of amino
acids, sugars, & other org. molecules
that supported Oparin’s hypothesis
So, how do organic molecules lead
to cells??
• Evolution of Cells
• 1st cells- protocells- large structure w/ a
membrane that contains the primordial
soup & carries out cell division
• Believed that prokaryotes evolved from
protocells
*Remember there is no free O2 present yet
• So, 1st prokaryotes were heterotrophic
anaerobes that ate primordial soup
Evolution of Cells
• So, 1st autotrophic bacteria made food (glucose)
by chemosynthesis by releasing energy of
inorganic molecules & lived in harsh
environments
*Similar to present day archaebacteria that live in
hot springs
• 2nd autotrophic bacteria may have been
photosynthesizing prokaryotes which released
O2 in the atmosphere
• Lightning striking the O2 would have formed O3
(ozone) and allowed more complex organisms
(eukaryotes) to thrive
Endosymbiont Theory
• *Believed that eukaryotes evolved from
prokaryotes
• 1960s- Lynn Margulis proposed this theory
• She said eukaryotes evolved by symbiotic
relationships w/ prokaryotes
Evidence to support Margulis’
beliefs
• Cyanobacteria & chloroplasts (contain
DNA & ribosomes) look similar & can both
do photosynthesis
• Some bacteria & mitochondria (contain
DNA & ribosomes) look similar