Topic 6: Origins of Life

Question 1

List the important events in the history of life in order

Answer 1

1. Formation of earth and the solar system
2. Prokaryotes emerge
3. Atmospheric oxygen emerges (and photosynthesis)
4. Single-celled eukaryotes emerge
5. Multicellular eukaryotes emerge
6. Animals emerge
7. Colonization of land
8. Humans emerge

Question 2

What is a fossil?

Answer 2

• preserved remnant/evidence of organisms that lived in the past
• associated with sedimentary rock (rocks formed through the accumulation of mud, silt, sand with distinct layers called strata)

Question 3

What does the fossil record tell us?

Answer 3

-it provides evidence of how life has changed over time

Question 4

What characteristics make an organism more likely to be fossilized?

Answer 4

• hard rather than soft-bodied
• aquatic than terrestrial (least likely to be exposed to oxidation or decomposition)
• inshore marine than offshore
• decomposing organisms absent

Question 5

What is relative dating?

Answer 5

• allows us to determine the relative order of past events
• can determine which stratum (layer) is older than another to determine the sequence, but can’t tell exact age (older fossils will be in bottom stratum and newer ones will be on the top)

Question 6

What is Absolute Dating?

Answer 6

• uses radioactive isotopes of elements in the rock to estimate the age of the rock
• determine using half-lives of isotopes (the amount of time needed for half of the atoms of the radioactive substance to decay)

Question 7

What is Continental Drift in terms of plate tectonics?

Answer 7

• land masses drift around on plates “floating” on the hot mantle
• this results in relative location of land masses to have changed over time
• tectonic boundaries (points where plates meet) are sites of earthquakes and volcanoes
  eg: ring of fire, east and west coast moving away from each other

Question 8

How do fossils provide evidence of continental drift?

Answer 8

The same genus of fossil plants was found on different continents, which gives evidence for all continents being one many years ago (Panagia)

Question 9

Explain the 2 consequences of continental drift

Answer 9

1. Change to the environment and climate
   - opportunities for the diversification of life (allopatric speciation)
   eg: when land masses are isolated, each can develop its own suite of species
2. Mass Extinction
   - will allow other species to colonize and diversify
   eg: when dinos went extinct when Antarctica drifted to the pole and froze

Question 10

Why is our fossil record biased and incomplete and what implications does it have?

Answer 10

• not all fossils are able to be preserved, some will decompose and not be in the record
• the intermediate stages of how some organisms came to be are missing
• can be interpreted as a punctualist theory where species evolve rapidly, or as gradualism (the intermediate stages exist but are missing from the record)

Question 11

What was the Hadean era?

Answer 11

• it was a time of great geological change in which the earth was formed
• at first, the earth was a molten ball of fire, that cooled to form a crust
• solid rocks floated on the melting magma
• the steaming gases from the cooling rock results in the forming of an atmosphere (that lacks oxygen)
• temp dropped and gases condensed and rained down
• when gases cooled we had a release of water vapor from the air, so the basins filled with water and formed transient oceans

Question 12

What are stromatolites?

Answer 12

• earth’s oldest fossils (3.5 billion years old)
• they are rocks with a distinctive layer structure
• layers of microbes and sediment (remains of living things)
• the top layer is used in photosynthesis
• lower layers use the byproducts of the first layer

Question 13

What was the primordial soup theory?

Answer 13

• a theory proposed by Alexander Oparin and John Haldane
• is a possible explanation for the creation of life
• under the weird conditions of the Hadean era, a soup-like nature of organic matter was formed, which came together to create life on its own

Question 14

What are the four steps in the creation of life (theory of spontaneous creation-abiogenesis)? Do they have to be sequential?

Answer 14

1. Abiotic synthesis of organic molecules (inorganic compounds to organic molecules)
2. Abiotic synthesis of macromolecules (make more complicated and longer chains)
3. Formation of protocells (membrane-enclosed compartments that hold molecules)
4. Self-replicating molecules
   - steps 1 and 2 have to be in sequence but steps 3 and 4 do not have to be in sequence

Question 15

Explain how the abiotic synthesis of organic molecules occurs

Answer 15

-energy (in the form of lightning, UV, collisions, deep-sea hydrothermal vent) is applied to organic gases (methane, ammonia, hydrogen, water vapor, CO2, nitrogen), which created organic molecules (amino acids, nitrogenous bases, sugars, lipids)

Question 16

Why is oxygen not included in the organic gases that formed organic molecules?

Answer 16

The absence of oxygen is necessary, or it will degrade the organic matter that is created

Question 17

How do we know that the theory of abiotic synthesis could be true?

Answer 17

• Miller’s experiment
• put inorganic gases in a chamber with water vapor, zapped with electricity, condensed the products out of the air, and analyzed them (replicated conditions of earth billions of years ago)
• they found organic molecules like amino acids and nitrogenous bases
• however, did not create life (can only make building blocks)

Question 18

Explain how the abiotic synthesis of macromolecules occurs?

Answer 18

• single monomer units will combine themselves into polymer units (amino acids, nitrogenous bases, sugars to proteins, enzymes, and nucleic acids)
• RNA monomers are produced spontaneously from simple molecules (can sometimes become a functional unit and cleave other molecules as enzymes do)

Question 19

What speeds up the process of monomers combining to form polymers?

Answer 19

• can put monomers under conditions of hot sand, clay, or rock and will combine spontaneously at faster rates
• happens in deep seas, would create more polymers than we would expect on their own

Question 20

Explain the formation of protocells

Answer 20

• lipid “bubbles” (hollow lipid vesicles) are formed, which creates a membrane that separates the organic molecules inside of the cell and from the outside of the cell
• a bi-layered structure similar to living cell membranes
• however, the free-floating amino acids, proteins, and nucleic acids would not have been able to behave like cells

Question 21

What are the advantages of having a lipid vesicle?

Answer 21

• this makes it easier to moderate conditions inside the cell and concentrates the organic molecules needed (more concentration of reactants=more products formed)
• cells would be able to keep or export their own products
• encourages the evolution of cooperative relationships
• houses DNA molecules (genetic info)

Question 22

What allows the lipid vesicle to form more rapidly?

Answer 22

• volcanic clay makes the reaction go faster

- allows the polymers to line up (adds structure)

Question 23

Describe basic characteristics of RNA

Answer 23

• first genetic material
• single-stranded, fragile, self-replicating
• can form different shapes depending on the environment
• can catalyze many different reactions (ribozymes)
• favored by natural selection (RNA world)
• evolved to become DNA (two strands aligned)

Question 24

Describe basic characteristics of DNA

Answer 24

• double helix: paired strands are twisted around each other
• very stable structure
• more accurately replicated-will retained at greater frequencies than RNA (also favored by natural selection)

Question 25

Explain how RNA could have led to protocells replicating

Answer 25

- gets captured in a protocell or evolved in a protocell - capable of copying itself, therefore it makes many copies - the cell volume goes up so the cell splits into two

Question 26

Why do scientists believe that RNA came first?

Answer 26

- DNA can only store information, it can not do functions, while proteins can perform functions, but not without instructions (genetic information) - therefore RNA must have come first because it can perform both functions-store information and perform tasks that keep the cell alive - eventually, RNA mutated into DNA

Question 27

Why don't we have actual evidence of which came first, DNA or RNA?

Answer 27

- are not able to preserve in fossils - organic things often decompose and teeny tiny things like DNA and RNA would not preserve well - can have preserved organic material but not RNA and DNA

Question 28

Where does life originate?

Answer 28

- hot, mineral-rich deep-sea vents - this is where many of the earliest derivative prokaryotes (Archaea) still live - experiments mimicking characteristics of underwater volcanoes produce more amino acids than those not mimicking them - the absence of oxygen gas is important (allows molecules to form organic things that don't decompose quickly)

Question 29

What is the extraterrestrial origin theory?

Answer 29

- life originated from outside the earth and was brought here - panspermia (seeds everywhere-asteroids brought these seeds of organic molecules to earth-enough energy on the asteroid to turn monomers into polymers) - ET transplant (life was dropped off here by other beings)

Question 30

What is the creation theory?

Answer 30

- creationism and intelligent design (there is some sort of god who created life) - FSM movement rose in opposition