Name __________________
Answers to the Chapter 12 Review 2010
1. What was early planet earth like? Earth was a ball of hot molten rock with no oxygen in the
atmosphere. Nothing could have lived here.
2. How old is the Earth? _______4.5 billion years old___
3. How do we know? Ancient rocks have been dated with radiometric dating.
4. What is an isotope? Isotopes are atoms of the same element with different numbers of neutrons,
therefore the atoms also have a slightly different atomic mass.
5. What is a radioisotope? Radioisotopes are just isotopes that are radioactive because their nucleus
is unstable.
6. How did James Hutton know that the earth had to be much older than anyone before him had
surmised? Hutton found rock formations that had obviously changed over time. He could see that
several sedimentary layers had been originally laid down horizontally. Then these layers were
tilted at an angle by an earthquake-type action and then eroded. Later still more sedimentary
layers had been laid down over the now tilted and eroded layers. Hutton knew that rocks couldn’t
form quickly so that for all this to have happened would have taken millions and millions of years.
7. Who is James Hutton anyway? He was the first real geologist and is called the ‘father of geology’.
8. What does the term half-life mean? The amount of time it takes for half of a particular amount of a
radioactive element to decay. Each radioactive element has its own specific half-life and nothing
affects the speed of the half-life. The half-life of carbon-14 is 5730 years so it would take 5730
years for a 10 grams sample of C-14 to decay to 5 grams.
9. If the half-life of potassium-40 is 1.3 billion years, how long would it take an 8 gram sample to
decay to 2 grams? Show all your work.
8 grams 0 years
4 grams 1.3 billion years
2 grams 2.6 billion years
So it would take 2.6 billion years to decay down to 2 grams.
10. What does the term radioactive decay mean? A radioactive element has an unstable nucleus so it
goes through radioactive decay. This means that it throws out energy and pieces of itself until it
gets down to a stable state. Since the atom actually loses protons, radioactive decay is the only
thing that can actually change one element into another.
11. What is Oparin and Haldane’s primordial soup model? They hypothesized that the gases in earth’s
early atmosphere reacted with each other, due to lightning and UV radiation, to form amino acids,
nucleic acids, lipids, and other molecules necessary for life. They then hypothesized that these
molecules would mix with the warm mineral filled ocean waters and react still further to form
proteins, RNA, and lipids.
12. What experiment did Miller and Urey do and what were the results of their experiment? Miller and
Urey set up an apparatus (in your book) that simulated the early oceans and atmosphere. They
then ‘zapped’ the atmosphere with electricity to simulate lightning and found that amino acids,
nucleotides, lipids, and other hydrocarbons had assembled and were in the ‘ocean’.
13. Why was Miller and Urey’s experiment reevaluated? Since there was no ozone layer in the early
earth’s atmosphere it was realized that methane (CH4) and ammonia (NH3) molecules would have
been immediately broken down by the UV rays.
14. What are the results of modern experiments like Miller & Urey’s? When there is no methane or
ammonia in the simulated atmosphere not all the life molecules can form.
15. So how did the molecules of life probably form on early earth and what is the model called? The
Lerman bubble model hypothesizes that the bubbles of sulfur, methane, ammonia, and other gases
that are emitted from deep ocean vents and undersea volcanoes is where the reactions took place
that formed amino acids, lipids, and nucleotides. Inside bubbles the gases would be more
concentrated and the ocean water would protect them from the UV radiation. Once the bubbles
got to the surface of the ocean they would burst and release their simple molecules which would
then react further due to the energy from the UV radiation. These heavier molecules would then
fall back into the ocean where they would react with other molecules to form more complicated
molecules. We do know that amino acids and RNA nucleotides will assemble into proteins and
RNA molecules respectively when clay particles are present.
16. What do the primordial soup model and the bubble model have in common? Both models have life
molecules developing without any living organisms present (and this has been done in labs today)
and both have live beginning in the warm seas.
17. Why is RNA most likely the nucleic acid used by early life and not DNA? Include three reasons.
RNA is a simpler molecule since it has only one strand instead of two. RNA is also a very versatile
molecule which can act as an enzyme, a template for protein synthesis, and it can replicate itself
without the help of other molecules. RNA can also form spontaneously in water. DNA can do none
of this.
18. What is a microsphere? A microsphere is a droplet/sphere made of short chains of amino acids.
These cell-like spheres can form spontaneously in water.
19. What is a coacervate? A coacervate is a cell-like sphere made of linked amino acids and sugars
that can also form spontaneously in water.
20. What is the significance of microspheres and coacervates? Both of these can form spontaneously
in water a make a membrane-like structure similar to the plasma membrane of a cell.
21. What is a fossil? A fossil is some type of remnant of an ancient organism. It can be bones or
footprints that have been turned to stone over time. Or it could be frozen remains or a small
organism trapped in amber.
22. The oldest fossils are 3.5 billion years old (your book has an error) and they are fossils of…
prokaryotes, a type of cyanobacteria that still has living relatives called stromatolites.
23. Why did oxygen begin to build up in the earth’s atmosphere? A type of prokaryotes, called
cyanobacteria began to carry out photosynthesis. These organisms lived in the oceans and once
the oceans were saturated with oxygen then the oxygen gas began to escape into the atmosphere
and began to build up.
24. What is the endosymbiosis theory and what is all the evidence that supports it? This theory says
that eukaryotic cells took in smaller prokaryotic cells and they established a mutualistic
relationship. Over time neither one could survive without the other. Mitochondria and
chloroplasts both appear to be ancient bacteria and are different from all the other cell organelles.
Both mitochondria and chloroplasts have their own DNA, different from what is in the nucleus.
This DNA also consists of a single loop of DNA just like in bacteria. The cell membranes of
mitochondria and chloroplasts are similar to that of bacteria and both organelles have their own
ribosomes which are also similar to bacterial ribosomes. Mitochondria and chloroplasts also make
their own proteins. They also reproduce on their own by the same method as bacteria (binary
fission).
25. What are the advantages of being multicellular? Multicellular organisms can separate different
types of chemical reactions from each other so they are more efficient. Having different types of
cells also allows cells to become specialized for a particular job and therefore be more efficient.
Multicellular organisms can also become more complicated.
26. What is a mass extinction? (Mass extinctions often determine the end of a period.) A mass
extinction is when a large number and type of organisms die. This is not really ‘sudden’ in our
sense of the word but on a geological time scale. The dinosaurs, for example it took over a
thousand years for all the dinosaurs to become extinct.
27. Why is our current time described as another mass extinction? A vast number of species are
becoming extinct everyday due to human activities. All the world’s large mammals are
endangered due to habitat destruction and/or poaching. Thousands of birds, insects, and plants are
being wiped out with the logging of rainforests, many before we even knew they existed or what
benefit they may have held for mankind. In developed countries acres of habitat are destroyed
everyday to build more houses, malls, and roads.
28. Why was the formation of the ozone layer important? The ozone layer protected any organisms
that came on land, from UV radiation. Until there was an ozone layer life could survive only in
the oceans.
29. Would there have been soil on land when plants first developed there? Explain. No, there would
have been only bare rock. Soil forms over centuries as rock is eroded and broken down by lichens
and mosses. Fertile soil also only develops as decaying plant and animal material are added to it.
30. What are mycorrhizae and why are they important? Mycorrhizae are the filaments of a type of
fungus that grows into the roots of plants. This is a mutualistic relationship. The plants are
provided with more water and minerals and the fungus gets food. Many plants cannot survive
without mycorrhizae. Most forest trees depend on mycorrhizae and don’t grow well without them.
31. What is mutualism? Mutualism is a type of symbiotic relationship in which both organisms
benefit.
32. What is an arthropod? Why are they significant? An arthropod is an animal with jointed legs, an
exoskeleton, and a segmented body. Today’s arthropods include spiders and insects. Arthropods
were the first land animals.
33. What are the two main types of fish? How are they different? There are jawless fish and jawed
fish. Jawless fish include sea lampreys which have a sucker for a mouth and attach to a host and
suck out body fluids. Jawed fishes have a regular mouth and can bite and chew food. This
allowed jawed fishes to become efficient predators and herbivores and diversify.
34. What did amphibians evolve from? Amphibians evolved from fish. Probably something similar to
today’s mudskipper which can live in the water or walk around on muddy shores. It is now known
that the change in one nitrogen base can cause the lower fins of a fish to be more leg-like.
35. What did reptiles evolve from? Why are reptiles better suited to live on dry land than amphibians?
Reptiles evolved from amphibians. Reptiles don’t have moist skin but have a watertight skin instead.
Reptiles also lay eggs with a tough leathery covering that keeps in the moisture so they do not have to
be laid in water.
36. What did birds evolve from? Birds evolved from a particular type of dinosaur. Archaeopteryx is
an example of a bird-like dinosaur.
37. What did mammals evolve from? Mammals also evolved from reptiles, such as therapsids. These
reptiles had complex teeth and their legs were underneath their body instead of out to the side as in
other reptiles. Dinosaurs and mammals evolved about the same time.
38. How did continental drift affect the evolution of species? As the continents drifted their climates
changed causing species to evolve or die out. When some continents were together common
species evolved. Later when those continents separated the common species were isolated from
each other on the different continents so they changed and evolved in their own separate ways.
39. What is continental drift? This is the movement of the continents over the earth’s surface
throughout geological time, due to plate tectonics.
40. Did humans and dinosaurs ever exist on earth at the same time? No!
41. How long did dinosaurs roam the earth? They roamed the earth during the Mesozoic Era which
includes the Triassic, Jurassic, and Cretaceous periods. This is from about 251 million years ago
to 65.5 million years ago, over 185 million years. Dinosaurs were really quite successful for a
long time.
42. How long have humans been on the earth? Modern humans have been around less than half a
million years.
See the geologic events below:
bya = billion years ago;
mya = million years ago
Some major occurrences in geologic time: Please use these dates & not the ones in your book!
Precambrian Era:
3.5 bya oldest fossil of a living organism a prokaryote
2.7 bya oxygen began to increase in the atmosphere
2.2 bya oldest fossil of eukaryotic cells
1.5 bya oldest multicellular eukaryotic fossils
600 mya first animals (sponges or jellies)
Paleozoic Era:
540 mya beginning of the ‘Cambrian explosion’, many new animals appear
500 mya beginning of the Ordovician, first land plants; first arthropods; first jawless fishes
440 mya mass extinction
430 mya early Silurian, first jawed fishes
400 mya early Devonian, first insects
370 mya late Devonian, first land animals called tetrapods
360 mya mass extinction
351 mya early Carboniferous, first reptiles; first seed plants
252 mya mass extinction
Mesozoic Era:
251-65.5 mya first dinosaurs; first flowering plants; first mammals
210 mya mass extinction
65.5 mya mass extinction
Cenozoic Era:
65.5-present first primates; first humans
current mass extinction