1. KEY CONCEPT The origin of life on Earth remains a puzzle.

2. Earth was very different billions of years ago.
There have been many hypotheses of Earth’s origins.
The most widely accepted hypothesis of Earth’s origins is the nebula hypothesis.
The solar system was
created from a rotating
cloud of gas and dust.
Computer models and
the Hubble telescope
support this hypothesis

3. Earth was molten and hot due to the bombardment of Asteroids, Meteorites, Comets, and radioactive elements.
4 bya, earth cooled to form the crust.
3.8 bya – Earth cooled, and water vapor condensed to form the seas. Looked brown. Contained iron. Earliest sedimentary rock
Hydrogen, carbon monoxide, and nitrogen gas were released.
Atmosphere was composed of – ammonia, water vapor, Methane, and carbon dioxide
This caused the sky to be
pinkish-orange and toxic.
No free oxygen yet – not until
2 bya.

4. Several sets of hypotheses propose how life began on Earth.
There are two organic molecule hypotheses.
Miller-Urey experiment
electrodes
heat source
amino acids
water
“atmosphere”
“ocean”
meteorite hypothesis

5. Miller and Urey experiment
Simulation of how life could have formed with the right “abiotic stew” and conditions.
able to create amino acids and other organic molecules such as nucleic acids in just one week
Abiotic stew consisted of:
Methane (CH4), ammonia (NH3),
Hydrogen (H), and water vapor
(H20)
Used spark of electricity –lightning
Proved that organic molecules
(Carbon) could be produced from
inorganic molecules.

6. Meteorite Hypothesis
1969 meteorite hit Murchison, Australia
Contained over 90 different amino acids (organic)
Proved that amino acids could have been present when Earth formed or arrived when meteorites or asteroids bombarded the Earth.

7. There are different hypotheses of early cell structure.
iron-sulfide bubbles hypothesis
Hot iron sulfide rising from the ocean floor combines with cold ocean water to form chimneylike -hydrothermal vents Proposed 4 bya these compartments acted as a cell membrane for the 1st cell

8. There are different hypotheses of early cell structure.
lipid membrane hypothesis
Lipid = fat
Liposomes- membrane-enclosed spheres which can be spontaneously produced could have lead to a bilayer (double) membrane surrounding organic molecules
1st cell membrane which led
to the 1st cell????????

9. A hypothesis proposes that RNA was the first genetic material
A hypothesis proposes that RNA was the first genetic material. (RNA came before DNA)
Ribozymes are RNA molecules that catalyze their own replication.
DNA needs enzymes to replicate itself.