Name __________________
History of Earth; Biology 4441 Chapter 19 Review 2013
Answer the following questions as you read chapter 19 in your textbook.
1. Is it possible to find fossils of extinct organisms? Explain.
Of course, most of the fossils we find are of extinct organisms, from bacteria to dinosaurs.
2. Describe three different types of fossils and give an example of each.
Actual bones, teeth, fur, feathers or other fragments of the organism.
3. Most types of fossils are in _sedimentary_ rock, but some fossils can also be found in substances
such as _amber__ which is really dried tree sap. Frozen or mummified organisms can also be
ancient and considered to be fossils.
4. Describe three types of information paleontologists can learn from fossils.
Paleontologists can see the types of organisms alive and what they ate, where they lived and the type of
environment they lived in. Some aspects of how they lived can also be seen.
5. What is relative dating?
This looks at different layers of rock to see which is older. The oldest layers are always laid down before
younger layers.
6. What is an index fossil?
An index fossil is one that is easily recognizable, is found in only a specific time period and occurs in
many places around the world. Such fossils can be used to date the layers they are found in to at least
their particular time period.
7. What is radiometric dating?
This type of dating using radioactive isotopes and compares the ratio of the radioactive isotope to its
decay product to determine the age of a fossil or rock layer.
8. What does the term half-life mean? Give an example.
Half-life is the amount of time it takes for half the amount of a radioactive element to decay. For
example, the half-life of C-14 is 5730 years, so if there was a 10 gram sample of C-14, after 5730 years
there would be 5 grams of C-14 left.
9. Why can carbon-14 only be used to date fossils that are 60,000 years old or less?
Since the half-life of C-14 is 5730 years, after that amount of time there is usually not enough C-14 left to
detect in an ancient organism.
10. How can older fossils be dated radiometrically?
Older fossils can be dated using other radioisotopes that have longer half-lives.
11. How did geologists establish the geologic time scale?
They looked at ancient rock layers, fossils and index fossils and put everything in order from oldest to
youngest. They noticed some major changes in fossils and rock layers so used those to divide the time
into eons, periods etc.
12. Describe three different processes that have affected life and earth’s history?
Geological events such as large volcanoes and movements of the continents/plate tectonics have affected
global climates and therefore life on earth. Astronomical events such as meteors have also had large
effects. Life itself has affected other life. For example, when photosynthetic organisms evolved and
added oxygen to earth’s atmosphere then other life forms could evolve.
13. What is macroevolution?
Evolution acting over long periods of time on a wide number and type of organisms.
14. What can cause new species to form?
major climate changes and competition between species
15. A clade is a group of organisms that all came from a common ancestor (see pages 516-517). How
do the rate of extinction and speciation affect the survival of a clade?
If the rate of speciation is higher than the rate of extinction then the clade will continue. If the reverse is
true then the clade will probably become extinct.
16. What does the term background extinction mean?
All species constantly struggle to survive due to competition with other species and changing
environmental conditions. This means that over time a few species will naturally go extinct. This
background extinction rate is low, less than 1%.
17. What is a mass extinction?
A mass extinction refers to a time period when a large number of species go extinct. In the past this was
due to major events such as large meteors striking earth, major movements of the tectonic plates or high
amounts of volcanic activity. The extinction of the dinosaurs is an example. Today the major cause of
extinction is humans wiping out the habitat of species or over-hunting them.
18. Does evolution always take place at the same rate?
No, sometimes evolution is slow as in gradualism and sometimes it is more rapid as in punctuated
equilibrium.
19. What is gradualism?
Darwin and Wallace discovered gradual evolution, the slow gradual change in a species over time.
20. What does it mean to say that a species is in equilibrium in relation to evolution?
A species that is well adapted to its environment and whose environment hasn’t changed much may be
virtually the same structurally for a very long time. Horseshoe crabs are an example. They have been
pretty much the same for millions of years even though they have continued to evolve genetically.
21. What is punctuated equilibrium?
Sometimes evolution occurs at a more rapid rate without gradual changes in-between. When the finches
arrived on the Galapagos Islands with few other species there and lots of open niches, the finch population
evolved rapidly into a number of different species. Each species filled a different niche. ‘Rapidly’ is a
relative term, it still took hundreds of years for the changes to occur.
22. What is adaptive radiation? Give an example.
Adaptive radiation is when once species, or a small group of species, evolves into several new species.
These species would form a clade since they would be descended from a common ancestor. An example
would be dinosaurs which be an adaptive radiation from reptiles.
23. What is convergent evolution? Give an example.
When two unrelated species evolve in very similar niches they often evolve similar characteristics.
Examples include the ostrich, rhea and emu as well as the pangolin, anteater and echidna.
24. What is coevolution? Give an example.
An evolutionary change in one organism may cause an evolutionary change in another organism. This
occurs when two organisms are dependent on each other for survival. For example the moth with a 40 cm
tongue that is long enough to reach the nectar in a particular flower. Or a particular orchid that evolves to
look like the female of the bees that pollinate it.
25. 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.
26. How old is the Earth? _______4.5 billion years old___
27. How do we know? Ancient rocks have been dated with radiometric dating.
28. 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.
29. What is a radioisotope? Radioisotopes are just isotopes that are radioactive because their nucleus
is unstable.
30. 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.
31. Who is James Hutton anyway? He was the first real geologist and is called the ‘father of geology’.
32. What is the law of superposition? This simply states that the oldest rock layers & fossils would be
the lowest or deepest layers of undisturbed rock.
33. 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.
34. 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.
35. 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.
36.
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.
37. 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’.
38. 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.
39. 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 but many still do.
40. 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. Life may also have started around
the deep ocean vents themselves.
41. 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.
42. 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.
43. What are microspheres & coacervates? A microsphere is a droplet/sphere made of short chains of
amino acids. These cell-like spheres can form spontaneously in water. A coacervate is a cell-like
sphere made of linked amino acids and sugars that can also form spontaneously in water.
44. 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.
45. What are archaea?
Archaea are a kingdom of bacteria-like organisms that are very ancient. Their cell walls and metabolic
processes are different from those of bacteria and archaea can live in extreme environments such as the
hot springs of Yellowstone National Park.
46. What is a fossil?
A fossil is an ancient organism that has been preserved by some method.
47. The oldest fossils are 3.5 billion years old and they are fossils of…
stromatolites, which are layers of prokaryotes and their wastes.
48. Why did oxygen begin to build up in the earth’s atmosphere?
Photosynthetic prokaryotes evolved and began producing oxygen.
49. What is the endosymbiotic theory and what is the evidence that supports it?
Mitochondria and chloroplasts were once free-living prokaryotes that became part of eukaryotic cells.
Both mitochondria and chloroplasts have their own DNA, divide on their own by binary fission and
have a double phospholipid bilayer all just like a prokaryotes.
50. Why is sexual reproduction important? Sexual reproduction increases the genetic variability in a
species so natural selection is more likely to be able to occur.
51. Why is our current time described as another mass extinction? A high number and variety of
species are being wiped out by human actions such as building roads, malls and houses. Also
clearing deciduous forests and rain forests for paper and grazing beef or growing coffee is
destroying habitat and many species.
52. Why was the formation of the ozone layer important? The ozone layer protects living things on
earth from the harmful UV rays from the sun. Without the ozone layer life cannot exist on the
surface of the planet.
53. Would there have been soil on land when plants first developed there? Explain. Only a very poor
soil would have existed when plants first appeared. There would have been weathered rock but
not as much organic matter s there is today since there weren’t as many organisms leaving their
wastes and dead bodies to decay and add nutrients to the soils. There were bacteria though.
54. How did/does continental drift affect the evolution of species? As the continents move away or
toward the equation their climates change drastically causing the selection pressures to change.
The movement of the continents also affects the path of ocean currents which can also cause
drastic changes in global climate.
55. What is continental drift?
Movement of the continents caused by the shifting and movement of the tectonic plates
56. Did humans and dinosaurs ever exist on earth at the same time? ________NO_________
57. How long did dinosaurs roam the earth? From the Triassic to the Cretaceous periods, about 230
million years ago to 66 million years ago.
58.
How long have humans been on the earth? Modern humans have been on earth about 200,000
years
59. Know the main events on the geological time scale and what era they occurred in.
See pages 560 to 563 in your textbook.