1. Origins of Life
Chapter 12
Section 3
pg. 368

2. Nebula Hypothesis
Most widely accepted
hypothesis of Earth’s origins
States the solar system was formed by a condensing nebula
Nebula – cloud of dust and gas in space

3. Nebula Hypothesis Sun formed from nebula
Over time material in the nebula pulled together due to gravity
Materials that remained in the nebulas disk circled the newly formed sun
Repeated collisions of this space debris built up into the planets of our solar system

4. Nebula Hypothesis
Hadean Eon – first 700 million years of Earth, it was hot and violent
Many asteroids and meteorites struck the planet, releasing heat, trapping elements deep in the earth
These turned into earths layers and released elements into the atmosphere

5. Organic Molecule Hypothesis
Two hypothesis about how life supporting molecules appeared on early Earth.
Miller-Urey Experiment
Meteorite Hypothesis

6. Miller Urey Experiment
Proposed an input of energy from lightning led to the formation of organic molecules from inorganic molecules present in Earths atmosphere.

7. Miller Urey Experiment
Miller and Urey built a system to test this hypothesis
They demonstrated organic molecules could be made by passing an electric current through gas

8. Meteorite Hypothesis
Analysis of a meteorite revealed that organic molecules can be found in space
More than 90 amino acids were found on the meteorite, 19 naturally occurring on Earth.
Suggests amino acids could have been present when Earth formed, or that these organic molecules arrived on Earth from a meteorite.

9. Early Cell Structure Hypothesis
Two hypotheses about how the first cells may have formed on Earth
Iron-sulfide bubbles hypothesis
Lipid membrane hypothesis

10. Iron-sulfide Bubble Hypothesis
Hot iron sulfide mixed with cool ocean water form chimney like structures with many compartments.
It is proposed that 4 billion years ago biological molecules combined in these compartments.

11. Iron-sulfide Bubble Hypothesis
These compartments acted as the first cell membranes, holding the organic molecules in small compartments.
From here, cell membranes formed.

12. Lipid Membrane Hypothesis
Proposed that evolution of lipid membrane was a crucial step for the origin of life.
Lipid molecules spontaneously formed liposomes (membrane enclosed spheres)
Liposomes could then form around organic molecules and act as membranes that separated these molecules from the environment
Gave rise to the first cells

13. RNA as Early Genetic Material
Hypothesis that states RNA as the genetic material on early Earth

14. Ribozymes RNA molecules that can catalyze specific chemical reactions.
Ribozymes catalyze replication and synthesis
DNA can’t do this!