Unit 3: History of Life Flashcards
How long ago did Earth form?
~4.5 billion years
What was Earth like soon after it formed?
Hot (heavy bombardment)
No liquid water
Not much O2
A lot of N2, CO2, CH4, NH4, and H2
The first life on Earth
(describe)
Simple, prokaryote-like (no organelles)
Self-replicating molecules wrapped in membrane
When did the first cells appear on Earth?
Between 1/2 and 1 billion years after the Earth formed
e.g. about 3.5 - 4 billion years ago
What happened between the first prokaryotic cells on Earth and the first eukaryotic cells?
Photosynthesis, which lead to an
oxygenic atmosphere
What four steps lead to the formation of the first cells on Earth?
- Abiotic synthesis of small organic molecules
- Polymerization of those small organic molecules into polymers
- Packaging of polymers into protocells
- Self-replication of molecules / protocells
Outline Operin & Haldane’s hypothesis
Earth’s early conditions would have allowed the production of complex organic molecules because:
* Molecules in the atmosphere were reducing, meaning they provided the electrons needed for the formation of organic molecules; and
* Lightning and UV radiation would have supplied the energy necessary to build complex molecules
Outline the Miller & Urey Experiment
- What hypothesis was being tested?
- How?
- What did it show?
Tested Operin & Haldane’s hypothesis
Made lab set-up that mimicked Early Earth
Demonstrated that organic compounds could form in the absence of living organisms
What were the parts of the apparatus used by Miller & Urey?
- A chamber for gases, including those that would have been present in Early Earth
- An electrode, which mimicked the lightning strikes that were frequent in Early Earth
- A condenser to cool the gases
- A chamber for liquids, including water and any liquid that was formed from the other parts of the apparatus, and could be heated to vaporize the liquids
What are
Protocells
“Early cells”
Droplets of organic molecules with membranes around them, whose contents differ from the surroundings
What was likely the first genetic material?
RNA / Ribozymes
Why is DNA unlikely to have been the first genetic material?
DNA codes for proteins but needs proteins to make more DNA
Ribozyme
An RNA-based molecule that both 1) carries genetic information and 2) can act as an enzyme to help in its replication
RNA World Hypothesis
RNA was probably the first genetic material, which eventually gave rise to a system where one molecule held genetic information (DNA), while another catalyzed its replication (protein)
