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Origin of Life – Solutions
1. a. Origin of the Earth http://www.youtube.com/watch?feature=player_embedded&v=8brEo1_7Iro
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Time frame: Earth formed 4.55 billion years ago from a collection of gas and
dust.
Conditions: Primitive atmosphere  water vapour, carbon dioxide, nitrogen
gas, nitrous oxides, hydrogen gas, ammonia, methane, hydrogen sulfide; no
free oxygen (O2) so organic compounds could not break down as quickly;
energy sources  lightning, UV radiation, volcanoes; mostly water on surface
of Earth
Evidence: C. Patterson dated Canyon Diablo
Meteorites and calculated Earth to be 4.55 billion years
old; Miller and Urey’s experiment that incorporated
compounds present in hypothesized “primitive”
atmosphere  produced some organic compounds
(building blocks of life) like amino acids, adenine (a
nucleotide), hydrocarbons
b. Prokaryotes
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Time frame: 3.5 billion years ago, and solely
dominated the earth up until 2.0 billion years ago
Conditions: Lighting as an energy source converted
compounds from primitive atmosphere into small
organic molecules called monomers (e.g. amino acids,
nucleotides, fatty acids and simple sugars), which in
time combined to form organic polymers (e.g. proteins,
nucleic acids, lipids and carbohydrates). Then, these
organic polymers were packaged into droplets called
protobionts which contain compartmentalized
membranes. Successful protobionts evolved to make
at least some of the molecules it needed to survive.
These early prokaryotes used primitive compounds and
sunlight in order to photosynthesize.
Evidence: Oldest known prokaryotes were in the form
of stromatolites which are fossilized mats of
prokaryotes (layers of fossilized bacteria and
sediment).
c. Oxidizing atmosphere
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Time frame: oxygen begins to accumulate 2.7 billion
years ago
Conditions: biological origin within the ocean (i.e. as
a result of first photosynthetic bacteria called bluegreen algae or cyanobacteria). Oxygen within the
ocean reacted with iron to produce iron oxide, which
produced sediments in the form of bands on rock.
Oxygen, over time, was then released into the
atmosphere.
Evidence: banded iron in rocks (rusting)
d. Eukaryotic cells
http://www.youtube.com/watch?v=nc6ddfWK0sA
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Time frame: first eukaryotic cells appear approximately 2 billion years ago
Conditions: formed by Endosymbiosis. This started with the development of internal
membranes (i.e. infolding of prokaryotic plasma membrane, forming eukaryotic cells with ER,
golgi, and nucleus). Eukaryotes developed the ability to respire (i.e. use the oxygen from the
atmosphere) by ingesting but not digesting aerobic bacteria (that have mitochondria). Some of
these eukaryotic cells developed the ability to respire and photosynthesize by engulfing but not
digesting a photosynthetic bacteria (that have chloroplast. This evolution occurred because it
was beneficial to both parties  the host would get the nutrients released from the bacteria, and
in turn it would be protected form the oxygen outside the cell.
Evidence: mitochondria and chloroplasts  resemble bacteria in terms of structure, have their
own circular DNA (like bacteria), can move freely within the cell and can reproduce
independently from the cell.
2. The discovery of iron oxide bands in sedimentary rock was significant because it proved that there
was a significant amount of oxygen in the atmosphere starting at about 2.7 billion years ago. It was
also significant because something must have caused the existence of oxygen, when there was none
before that. This provides evidence for the existence of the first photosynthesizing bacteria
(cyanobacteria).
3. Theory of Endosymbiosis.
In general:
5. The Cambrian Explosion.
The Cambrian Explosion was “special” because in a relatively short period of
time (i.e. 10-20 million years) most of the major phyla of animals appear in
fossil record (e.g. sponges, cnidarians, chordates, etc.) This occurred 543
million years ago. Animals appeared that have hard shells or exoskeletons,
many still in water.
6. Some adaptations essential for the invasion of plants onto land:
 Water resistant (waxy) coating on their leaves so they don’t lose water (dehydrate).
 Vascular system so they could soak up water from deep within the ground and air and store it in
their leaves (to be used when needed).
 Thick cell wall for structure and support
 Stomata (pores in leaves) to allow water and nutrients in and out of the plant.
 Colonization with fungi  fungi help absorb water and minerals form the soil, while fungi obtain
nutrients from plant (symbiotic relationship)
8. See question #1a.
10. Four stages for the formation of life:
a. Synthesis of organic monomers (e.g. amino
acids, fatty acids, nucleotides, simple sugars)
b. Joining of monomers to form organic polymers
(e.g. protein, lipid, DNA/RNA, carbohydrates)
c. Formation of droplets called Protobionts that
undergo simple metabolism and reproduction
d. Origin of self-replicating molecules that made
inheritance possible
12. RNA is thought of to be the first genetic code because it is a lot less sophisticated than DNA and we
know that DNA evolved from RNA. RNA plays a central role in the making of proteins. The ribosomes
use the RNA to make the proteins. RNA when it was first around was very short and as time went on,
they became more adaptive, longer and eventually developed DNA and the double-helix structure. RNA
became DNA through many years of mutation and natural selection to make the genetic material better.
13. Oparin and Haldane, Miller and Urey
In 1920, Oparin and Haldane proposed the compounds that made up the “primitive atmosphere” (e.g.
methane, hydrogen gas, ammonia, water vapour and lightning as energy source).
In 1953, Miller and Urey tested Oparin and Haldane’s hypothesis about the “primitive atmosphere”
using the apparatus shown below. Organic molecules (e.g. adenine and amino acids) were appeared
after a few days. This proved Oparin and Haldane’s hypothesis about gases in “primitive atmosphere”
but also showed that molecules present in living things could have been “created” from the presence of
certain compounds found within the primitive atmosphere.
17. Problems with 5 kingdom classification system (monera, protista, plantae, fungi, animalia):
a. Monera too diverse (should be 2 distinct lines of prokaryotes  bacteria and archae)
b. Protists are still too diverse (part of Eukarya, but not yet sorted out)
20. membrane transport (along with formation of membrane), nucleic acid replication (DNA/RNA
replication), photosynthesis, fermentation (anaerobic respiration – no oxygen required), aerobic
respiration.
21. See question 13 above.
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