1. The Origin of Life

2. The Origin of Life is Hypothesis
Special Creation
Was life created by a supernatural or divine force?
not testable
Extra-terrestrial Origin
Was the original source of organic (carbon) materials comets & meteorites striking early Earth?
testable
Spontaneous Abiotic Origin
Did life evolve spontaneously from inorganic molecules?

3. Early conditions on Earth
Reducing atmosphere
water vapor (H2O), CO2, N2, NOx, H2, NH3, CH4, H2S
lots of available H & its electron
no free oxygen
Energy source
lightning, UV radiation, volcanic
It is unclear whether young Earth’s atmosphere contained enough methane and ammonia to be reducing. Growing evidence suggests that the early atmosphere was made up primarily of nitrogen and carbon dioxide and was neither reducing nor oxidizing (electron–removing). Miller–Urey–type experiments using such atmospheres have not produced organic molecules. Still, it is likely that small “pockets” of the early atmosphere—perhaps near volcanic openings—were reducing.
Instead of forming in the atmosphere, the first organic compounds on Earth may have been synthesized near submerged volcanoes and deep–sea vents—weak points in Earth’s crust where hot water and minerals gush into the ocean.

4. Conditions on Early Earth
Reducing atmosphere
water vapor (H2O), CO2, N2, NOx, H2, NH3, CH4, H2S
lots of available H & its electron
no free oxygen
Energy source
lightning, UV radiation, volcanic
low O2 = organic molecules do not breakdown as quickly
It is unclear whether young Earth’s atmosphere contained enough methane and ammonia to be reducing. Growing evidence suggests that the early atmosphere was made up primarily of nitrogen and carbon dioxide and was neither reducing nor oxidizing (electron–removing). Miller–Urey–type experiments using such atmospheres have not produced organic molecules. Still, it is likely that small “pockets” of the early atmosphere—perhaps near volcanic openings—were reducing.
Instead of forming in the atmosphere, the first organic compounds on Earth may have been synthesized near submerged volcanoes and deep–sea vents—weak points in Earth’s crust where hot water and minerals gush into the ocean.

5. Earth = 4.6 billion years old
First life forms appeared ~3.8 billion years ago
How did life arise?
Small organic molecules were synthesized
Small molecules  macromolecules (proteins, nucleic acids)
Packaged into protocells (membrane-containing droplets)
Self-replicating molecules allow for inheritance
“RNA World”: 1st genetic material most likely RNA
First catalysts = ribozymes (RNA)

6. Synthesis of Organic Compounds on Early Earth
Oparin & Haldane:
Early atmosphere = H2O vapor, N2, CO2, H2, H2S methane, ammonia
Energy = lightning & UV radiation
Conditions favored synthesis of organic compounds - a “primitive soup”

7. Tested Oparin-Haldane hypothesis Simulated conditions in lab
Miller & Urey:
Tested Oparin-Haldane hypothesis
Simulated conditions in lab
Produced amino acids
produced
-amino acids
-hydrocarbons
-nitrogen bases
-other organics

8. Protocells & Self-Replicating RNA

9. Fossil Record: used to reconstruct history
Sedimentary rock (layers called strata)
Mineralized (hard body structures)
Organic – rare in fossils but found in amber, frozen, tar pits
Incomplete record – many organisms not preserved, fossils destroyed, or not yet found

11. Both used to date fossils and determine age
Relative Dating
Radiometric Dating
Both used to date fossils and determine age
Uses order of rock strata to determine relative age of fossils
Measure decay of radioactive isotopes present in layers where fossils are found
Half-life: # of years for 50% of original sample to decay

12. Clock Analogy of Earth’s History

13. Key Events in Life’s History
Origin of Cells (Protobionts)
lipid bubbles  separate inside from outside
 metabolism & reproduction
Origin of Genetics
RNA is likely first genetic material
multiple functions: encodes information (self-replicating), enzyme, regulatory molecule, transport molecule (tRNA, mRNA)
makes inheritance possible
makes natural selection & evolution possible
Origin of Eukaryotes
endosymbiosis
The earliest living organisms were prokaryotes.
About 2.7 billion years ago, oxygen began to accumulate in Earth’s atmosphere as a result of photosynthesis.
Eukaryotes appeared about 2.1 billion years ago.
Multicellular eukaryotes evolved about 1.2 billion years ago.
The colonization of land occurred about 500 million years ago, when plants, fungi, and animals began to appear on Earth.
O2 accumulates in atmosphere
(2.7 bya)
Humans
(200,000)

14. Endosymbiont Theory
Mitochondria & plastids (chloroplasts) formed from small prokaryotes living in larger cells
Evidence:
Replication by binary fission
Single, circular DNA (no histones)
Ribosomes to make proteins
Enzymes similar to living prokaryotes
Two membranes
Evidence
structural
mitochondria & chloroplasts resemble bacterial structure
genetic
mitochondria & chloroplasts have their own circular DNA, like bacteria
functional
mitochondria & chloroplasts move freely within the cell
mitochondria & chloroplasts reproduce independently from the cell

15. Pangaea = Supercontinent Formed 250 mya
Continental drift explains many biogeographic puzzles
Continental drift is movement of Earth’s continents on great plates that float on the hot, underlying mantle. The San Andreas Fault marks where two plates are sliding past each other. Where plates have collided, mountains are uplifted.
Continental drift can help explain the disjunct geographic distribution of certain species, such as a fossil freshwater reptile found in both Brazil and Ghana in west Africa, today widely separated by ocean.

16. Mass extinctions  Diversity of life
Mass extinctions, loss of large numbers of species in a short period, have resulted from global environmental changes that have caused the rate of extinction to increase dramatically.
Adaptive radiations are periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological niches. Example: Galapagos finch species.
Major periods in Earth’s history end with mass extinctions and new ones begin with adaptive radiations

17. Major events during each Era
Precambrian: microscopic fossils (stromatolites)
Photosynthesis, atmospheric O2
Eukaryotes (endosymbiont theory)
Paleozoic: Cambrian Explosion
Plants invade land, many animals appear
Permian Extinction (-96% species)
Mesozoic: “Age of Reptiles”, dinosaur, plants
Formation of Pangaea supercontinent
Cretaceous Extinction – asteroid off Mexico’s coast
Cenozoic: Primates
Note: All end with major extinction & start with adaptive radiation

18. Need Help? Here are Some Extra Resources:
Bozeman Biology: Origin of Life Video
PBS NOVA: Origin of Life