AP: CHAPTER 26: ORIGIN OF LIFE

1. Start with the origin of the earth and identify the time frame, conditions, and evidence for each of the following steps leading to current life forms on earth.

*bya- billions of years ago....
a. Origin of the earth
Time Frame: 4.6 bya, Archaen Eon
Conditions: Condensed from vast cloud of dust and rocks surrounding the sun to create a reducing atmosphere- huge chunks of rock & ice were bombarding the planet filled thick with water vapor and compouds released by volcanoes.
Evidence: Miller & Urey performed an experiment by creating lab conditions to those that existed on early Earth- yielded amino acids found in organisms today & other organic compounds.

beal. . . right

b. Prokaryotes
Time Frame: 3.2 bya, Archaen Eon
Conditions: The first protobionts used molecules for growth & replication found in the primitive soup. Some had to make molecules that they needed. These protobionts were replaced by organisms that could produce all needed compounds. These autotrophs and heterotrophs were the first prokaryotes.
Evidence: Stromatolites (rocklike structures composed of bacteria and sediment) from 3.5 bya.

beal. . . right

c. Oxidizing atmosphere
Time Frame: 2.7 bya Archaen Eon
Conditions: Only living photosynthetic prokaryotes = cyanobacteria. Oxygen produced by cyanobacteria probably dissolved into water until seas and lakes became saturated with oxygen. The oxygen reacted with iron to form iron oxide and the oxygen entered the atmosphere. The oxygen created compounds that could attack chemical bonds & inhibit enzymes and damage cells; began cellular respiration.
Evidence: Rusted iron-rich terrestrial rocks, implies cyanobacteria originated as early as 3.5 bya

beal. . . right

d. Eukaryotic cells
Time Frame: 2.1 bya, Archaen Eon
Conditions: Evolved when oxygen revolution began to transform Earth's environment. They have cytoskeletan and can change shape = can surround & engulf other cells, can shift internal structures & facilitates movement of chromosomes in mitosis & meiosis.
Evidence: Traces of molecules found in rocks dating back 2.7 billion years

beal. . . right

e. Multicellular life
Time Frame: 1.2 bya, Archaen Eon
Conditions: According to Snowball Earth hypothesis, most life would have been confined to areas near deep-sea vents & hot springs or areas of the ocean where ice had melted.
Evidence: Fossil Record

beal. . . right


2. What was significant about the discovery of the iron oxide bands in the sedimentary layers.


· Implies cyanobacteria may have originated 3.5 bya
· Valueable source of iron ore today beal. . . not needed, but oxygen was a game changer for planet Earth!
· Evidence of oxygenic photosynthesis

3. Describe the theory of Endosymbiosis
Endosymbiont= cell that lives in another cell (host cell)
Probably led to mitochondria and plastids. Mitochondria and plastids were said to be prokaryotes living within larger cells. the ancestors of mitochondria were aerobic heterotrophic prokaryotes that became endosymbioints' the ancestors of plastids were photosynthetic prokaryotes that became endosymbionts.

beal. . . hmmmmmm. . . keep it simple. . . larger prokaryotes engulfed smaller ones as food or because the smaller ones could do something for the larger like make energy. this set the stage for co-evolution between the two prokaryotes where the smaller evolved into today's organelles.



4. Why did evolution seem to slow 750 to 570 million years ago?
Evidence shows that a sever ice age occurred 750 to 570 million years ago. Glaciers covered land masses from pole to pole and seas were iced over.

beal. . . right!

5. What was special about the Cambrium Explosion?
Most of the major phyla of animals appear suddenly in fossil record during the Cambrian period called the "Cambrium Explosion". It shows the phyla of animals expanded in diversity suddenly and simultaneously.

beal. . . right!


6. Describe a few adaptations essential for the invasion of plants onto land.
Adaptations were made that helped prevent dehydration such as a wax coating on leaves to help retain water. Adaptations were also made to make reproduction possible. Plants and fungi began a symbiotic relationship. The fungi aids plants with absorbtion of water and minerals from the soil. In return, the fungi recieved organic nutrients necessary from plants.

beal. . . what about seeds and their coats!


7. Scientific Hypothesis for the origin of life (briefly elaborate or explain each of these)

a. The first cells may have originated by chemical evolution on a young Earth
Energy for early organic synthesis came from lightning and UV radiation.

beal. . . life on Earth developed from nonliving materials that turned into aggregates that were capable of self replication and had a metabolism.


b. Abiotic synthesis of organic monomers is a testable hypothesis
Dropping solutions of amino acids on hot rocks and polymers just formed.

beal. . . Both A.I. Oparin and J.B.S. Haldane in the 1920’s stated that conditions on early Earth allowed for the synthesis of organic compounds from inorganic ones.


c. Laboratory simulations of early-Earth conditions have produced organic polymers
Liposomes can form when lipids are added to water.

This hypothesis predicts that monomers link to form polymers without enzymes or other cellular equipment. Scientists produced polymers by dripping solutions of monomers into hot sand, clay, or rock.

beal. . . good. . . called dehydration synthesis!

d. RNA may have been the first genetic material
RNA can carry out enzyme like functions.

beal. . . what else. . . more here! RNA is used for coding and has multiple functions like mRNA, rRNA, tRNA, etc. .


e. Protobionts can form by self-assembly
Liposomes can form when lipids are added to water.

Protobionts can maintain an internal environment that is different form their environment. They also show some properties of life, metabolism, and excitability.

f. Natural selection could refine protobionts containing hereditary information
Protobionts containing useless things can be eliminated by natural selection.

beal. . . ah. . . you didn't answer the question. here we have an internal environmnet that can evolve seperately from the outside!

g. Debate about the origin of life abounds
Life could have come from meteors or from other planets


8. Describe the hypothesized conditions on earth when life arose

Atmosphere was thick with water vapor; volcanic eruptions; nitrogen and oxides; CO2, methane, amonia, hydrogen, and hydrogen sulfide. As earth cooled, water vapor condensed and hydrogen moved into space.

beal.. . . and then what? what was formed?

9. What did Louis Pasteur demonstrate with his experiment?

Louis disproved spontaneous generation of microorganisms. He set up an experiment in which air and no microorganisms was allowed to contact a broth that contained nutrients.

beal. . . good!

10. List the four stages for the formation of life.
a. Abiotic synthesis of small molecules

b. Joining of these smaller molecules into polymers

c. Packaging of these molecules into "protobionts"

d. Origin of self-replicating molecules that eventually made inheritance possible

beal. . . good!

11. What metabolic processes would you expect to see in protobionts?
You would expect to see simple reproduction and metabolism, as well as the maintenance of an internal chemical environment different from that of their surroundings.

beal. . . good!


12. Why is RNA now thought to be the first genetic code?
It is considered to be the first genetic code because it is multi-functional, is a regulatory molecule and transport molecule, and it carries out enzyme-like catalytic functions.

beal. . . good!


13. What did Oparin, Haldane, Miller and Urey accomplish?


Oparin and Haldane hypothesized that early Earth was a reducing environment. Miller and Urey set up an experiment to determine original conditions on Earth. They proved that organic molecules can form in a reducing atmosphere.

beal. . . and what was the outcome of their experiment?


14. What are some of the possible locations for the first life forms?


Thermal vents, less light exposed sea floor, shallow water and moist areas are all possible locations.

beal. . . good!