Biology Chapter 12 Section Review Questions and Answers

what were some of the key appearances and radiations of the mesozoic era?

- began 251 million years ago and ended 65 million years ago - dinosuars roamed the earth - marsupials had evolved to survive the mass extinction - the fossil record shows that the first mammals evolved during this era - evidence shows that a meteorite hit the earth and killed the dinosaurs (the most accepted hypothesis is that the impact sent enormous amounts of dust and debris into the air, blocking much of the sun's light)

what important events occurred during the paleozioc era?

- began 542 million years ago - members of every major animal group within only a few million years - ended 251 million years ago with a mass extinction - more than 90% of the marine animal species and 70% of land animal species of that time became extinct - in between this time multicellular animals evolved, the first vertebrates evolved, and early plats moved onto land - the cambrian explosion took place

how early did cyanobacteria affect the physical and chemical conditions on the earth?

3.5 billion years ago.

in radiometric dating, why is a uranium isotope often used instead of carbon-14 to determine the age of the earth?

because carbon-14 only has a half-life of 5730 years, while any uranium isotope has a half-life of around 4 billion years.

what types of evidence of ancient life can be preserved as fossils?

bones, shells, tissue (rarely), nests, footprints, plants, insects, etc can all be fossilized.

examine the illustrations of the paleozoic, mesozoic, and cenozoic ears in this section. what differences can you see in plant and animal diversity across the eras?

during the palezoic era the animals mainly consisted of reptiles, amphibians, and marine life. the cenozoic era was mostly dinosaurs and was the start of mammals. then the mesozoic era was different species of mammals mostly. vegetation wise the palezoic and the cenozoic eras mostly consisted of ferns while the mesozoic era consisted of pine trees and evergreens.

the most common index fossils are shells of invertebrates. give two reasons why this is so.

fusulinids make good index fossils. they are very abundant in marine sediment, widely distributed, and existed during a specific period in time.

according to the fossil record, what other homo species was preset when modern humans arose?

homo neanderthalensis

from the hominid fossils described, what common trends can be found?

human evolution would not have advanced as it did without an enlarging skull and brain size. throughout the millenia our skulls have been becoming more rounded and have enlarged, while our brains have been changing in size (decreasing and increasing).

how are index fossils used to date rock layers?

index fossils are fossils of organisms that existed only during specific spans of time and lived in large geographic areas. if an index fossil is found in a layer of rock, it means that the rock layer and other fossils found in that layer are the same age as the index fossil

how does a great diversity of organisms increase the chances that some will survive a major change in the environment?

just like animals change, so does land. so if you have different variations of a species in a population and some go extinct they will have the remaining to continue the species. if there were only one form of a species and they couldn't survive the environment change, then they'd become extinct.

describe the environmental conditions that are thought to have existed during the hadeon eon.

many asteroids, meteorites, and comets struck the planet, releasing enormous amounts of heat during the hadean period. the radioactive decay was also rising from the earth. this intense heat kept the earth in a molten state.

considering that millions of species have lived on earth, why are there relatively few fossils?

over time, pressure from additional sediment compresses the body, and the mineral slowly replaces all hard structures (such as bone), leaving practically nothing left over.

what two groups of mammals evolved during the cenozoic era?

placetal mammals and monotremes, a small group of mammals that lay eggs, evolved during the cenozoic era.

what characteristics shared by humans and other primates suggests that they have a common ancestor?

primates make yo a category of mammals with flexible hands and feet, forward-looking eyes (which allow for excellent 3d vision), and enlarged brains relative to body size. primate also have arms that can rotate in a circle around their shoulder joint, and many primates have thumbs that can moves against their fingers.

explain the difference between relative dating and radiometric dating.

relative dating is using the use of surrounding rock layers to get an approximate age, while radiometric (absolute) dating is the use of half-lives to determine an exact age.

how does sexual reproduction increase diversity among living things?

sexual reproduction allows new combinations of genes to come together, because both parents have a set of genes to offer, allowing harmful mutations to be masked at times and better mutations to arise.

how does sexual reproduction increase the chances that some individuals will survive changed environmental conditions?

sexual reproduction creates more genetic variation, which lets a population adapt quickly to new conditions. this use of natural selections allows some species to prevail over others.

the theory of impact frustration proposes that life may have started several times during the hadeon eon, but was interrupted by space debris hitting earth. what makes this theory difficult to test?

since the hadean era was so hot, it would be hard to start a species; and if in some case they were destroyed by a meteor all remains would have been destroyed by the immense heat/the power of the meteors impact.

what is the usefulness of categorizing earth's history into the geological time scale?

the geological time scale organizes earth's history by major changes or events that have occurred, using evidence from the fossil and geological records.

describe two different hypotheses of the origin of early cell structure.

the iron-sulfide bubbles hypothesis is believed that around 4 billion years ago biological molecules combined in the compartments of chimney-like structures; the compartment walls concentrated the basic organic molecules in a small space. the lipid membrane hypothesis is the belief that at some point liposomes were formed with a double, or a bilayer, lipid membrane. these liposomes could then form around a variety of organic chemicals.

how are the two organic molecule hypotheses different?

the irthe iron-sulfide hypothesis believes that molecules were combined and stored away in small compartment spaces, while the lipid membrane hypothesis believes that liposomes formed with a bilayer lipid membrane and then formed around an organic molecule.

scientists have inferred that there have been at least five mass extinctions in earth's history. how would fossil evidence support this inference?

the largest adaptive radiations tend to follow the largest mass extinctions. So by examining the fossils and following the adaptive radiation of a species you can find the niches that mass extinction has left.

how does the theory of endosymbiosis account for the evolution of eukaryotes?

the theory of endosymbiosis proposes that the first eukaryotic cells arose from a large prokaryote engulfing a smaller prokaryote.