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.
Sometimes also called the
Big Bang Theory
Age of Earth:
billion years old

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”

5. The Miller-Urey Experiment was based on Oparin’s Hypothesis:
Early Earth was warm, with lightning
Gases present: Water vapor, Hydrogen, Ammonia (NH3), Methane (CH4)
These combined to
make first organic molecules.
The Miller-Urey Experiment
made amino acids.
electrodes
heat source
amino acids
water
“atmosphere”
“ocean”

6. Meteorite Hypothesis
Amino acids may have arrived on Earth through meteorite or asteroid impacts.
Evidence: Scientists have found amino acids on meterorites.

7. There are different hypotheses of early cell structure.
Iron-sulfide bubbles hypothesis
Biological molecules first combined in compartments of chimmney-like structures on ocean floor
Compartments were first cell membranes.

8. There are different hypotheses of early cell structure.
Lipid membrane hypothesis
Lipid spheres (liposomes) could form around a variety of
organic molecules, acting
as early cell membranes.

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