Transcript Life on Earth ppt notes

Early Earth Conditions
Origin of Life Beliefs
1. The Big Bang Theory states that
all matter and energy in the
universe was compressed into an
extremely small volume that 10 to
20 billion years ago exploded and
began expanding in all directions
Origin of Life Beliefs
2. Meteorites
a. Life started when a meteorite containing
organic matter collided with the Earth
b. Could explain how organic molecules that are
necessary for cell formation arrived on Earth
and entered the oceans
3. Divine Origins (Intelligent Design)
a. Many major religions teach that life was created
by supreme being
1. Explain it as life could not have been created
without the intervention of a divine force
Origin of Life Beliefs
• 4. 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)
The Modern Ideas (continued)
5. Primordial Soup
a. Idea that Earth’s ancient atmosphere probably
contained nitrogen, methane, ammonia, and
carbon dioxide
1. Energy from sun, volcanoes, and lightning
fueled chemical reactions among these
gases, which combined into small organic
molecules like amino acids
2. Rain washed these molecules into the oceans
making…primordial soup!
b. Harold Urey and Stanley Miller provided
evidence to support this.
Early Earth Conditions
• According to the geologic time scale it’s
believed that the Earth formed approximately
4.6 billion years ago
• SO HOT!!! Due to radiation (left over from
big bang), 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 3.5 byo (billion years ago) earth
started to cool and H2O condensed to form
liquid H2O
*Rock evidence shows 1st signs of life
(from fossils) was around 3.5 byo
• Led to millions of years of rainstorms to form
the oceans
• Helps support Miller/Urey experiment
How do scientists believe life
began?
• SO HOW DID LIFE BEGIN ON EARTH??
• TO GET LIFE YOU NEED TO FORM
ORGANIC MOLECULES (CONTAIN
CARBON)!!!
Formation of Organic Molecules
• 1. Believed early atmosphere contained
little to none free O2
• 2. Most atmosphere was made of (water
vapor, carbon dioxide gas, nitrogen gas,
methane gas, ammonia, hydrogen gas,
and carbon monoxide)
Key point- No Free Oxygen Yet!!
• *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, nucleotides & other organic
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 (bacteria) evolved
from protocells
*Remember there is no free O2 present yet
Evolution of Cells Timeline
4.5 byo
3.5 byo
2.5 byo
1.5 byo
0.5 byo
3.5 byo- So, 1st prokaryotes were
non-photosynthetic bacteria
(heterotrophic anaerobes) that ate
primordial soup or others did
chemosynthesis & made own glucose
Evolution of Cells Timeline
4.5 byo
3.5 byo
2.5 byo
1.5 byo
0.5 byo
• 3.2 byo- 1st photosynthesizing prokaryotes
•
•
(autotrophic bacteria) evolved
which released O2 in the atmosphere
Evolution of Cells Timeline
4.5 byo
3.5 byo
2.5 byo
1.5 byo
0.5 byo
• 2.0 byo-2 major events occurred: Due to
•
the accumulation of oxygen the 1st
•
eukaryotic cells evolved…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