Evolution - Chapter 3 Book Questions

How do biomarkers add to our understanding of the history of life?

Biomarkers are specific kinds of traces left by living organisms; they are molecules that were formed through biological processes. For example, okenane functions as a biomarker because it is produced only by purple sulfur bacteria. Scientists don't know of any nonbiological source of okenane. As a result, the presence of okenane in rocks means that purple sulfur bacteria must have been around producing it before those rocks formed. Radiometric dating can indicate the age of the rocks, and scientists can gain insight into the history of life.

Why are fossils rare?

Fossils are rare for several reasons. Most important, not all animals' remains are left to be fossilized. Most animals are food for other organisms, so their bodies may not even be available to be fossilized. Moreover, organisms that die are left to the elements, like wind and rain, which can destroy any remaining evidence of their existence. If an organism is buried by sediments and its remains fossilize, paleontologists have to be able to access the rocks — and access them quickly. Over time the fossils themselves can again be exposed to the elements, destroying what is now pretty rare evidence. Soft tissues, like skin and organs, can be especially difficult because it takes an especially rare set of circumstances to mineralize and preserve these tissues.

What evidence refutes Kelvin's claim that Earth is only 20 million years old?

Kelvin didn't know that Earth's interior was dynamic — that within it hot rock was rising, cooling, and sinking. He assumed that the planet was a rigid sphere, so his model didn't account for the greater heat flow that results from this movement. More important, scientists figured out a way to measure the absolute age of rocks using decay rates of isotopes. Radiometric dating indicates that Earth formed as part of a dust cloud around the Sun 4.568 billion years ago.

Why do scientists believe that plants and fungi may have been integral to each other's colonization of dry land?

Scientists believe that plants and fungi may have been integral to each other's colonization of dry land because the oldest fossil fungi are found mingled with the early land plant fossils. Today, similar fungi live in close association with land plants and supply nutrients to their roots in exchange for the organic carbon that the plants create in photosynthesis.

How can scientists understand the behavior of extinct animals?

Scientists have found fossils that actually show different behaviors, such as live birth, predation, herding, and even parental care. In addition, scientists can examine the behavior of animals today and combine that knowledge with the physical evidence from fossils to develop hypotheses about how the extinct creatures lived. They can test their predictions with additional lines of evidence. So scientists can examine muscle attachment sites in the legs of T. rex, the organization of the melanosomes of fossil feathers, or the structure of nasal passages of hadrosaurs and compare those data to data from living animals. As a result, they can gain insight into how dinosaurs ran, how they may have used feathers in courtship display (a behavior common in modern birds), and how they communicated.

What are stromatolites, and why are they evidence of very early life?

Stromatolites are ancient rocks found in some of the oldest geological formations on Earth. They bear striking microscopic similarities to large mounds built by colonies of bacteria alive today. Although these formations are rare on Earth today, they are abundant in the early fossil record. So stromatolites are not only evidence of early bacterial life, they may also be important to understanding life on Earth 3.7 billion years ago.

Define prokaryote. a. A descriptive grouping for microorganisms that lack membrane-bound organelles. b. A grouping useful in the classification of early microorganisms. c. A grouping often used instead of Archaea. d. A single-celled eukaryote.

a. A descriptive grouping for microorganisms that lack membrane-bound organelles.

Which isotope would be useful for dating a fossil found in relatively recent sediments? a. An isotope with a moderately high probability of decay. b. An isotope with a low probability of decay. c. Rubidium. d. Strontium.

a. An isotope with a moderately high probability of decay.

Which of the following helped scientists determine that multicellular life arose more than once? a. Animals are more closely related to single-celled eukaryotes than to fungi. b. Fungi can produce multicellular structures. c. Bacteria live as multicellular groups called biofilms. d. Scientists have no idea if multicellular life arose more than once.

a. Animals are more closely related to single-celled eukaryotes than to fungi.

Which group is not considered one of the major lineages of all living organisms? a. Bacteria. b. Prokarya. c. Archaea. d. Eukarya.

b. Prokarya.

How did the fossils of the Burgess Shale likely form? a. The animals fell to the bottom of a deep lake and over thousands of years turned to rock. b. The animals dropped into anoxic ocean depths and were covered by fine sediment. c. The animals were rapidly covered by ash falling from a volcano. d. Shallow seas disappeared, exposing mud sediments to the air.

b. The animals dropped into anoxic ocean depths and were covered by fine sediment.

Why is a notochord an important adaptation for understanding the evolution of humans? a. The development of a notochord occurred in early fishes. b. A notochord is a backbone. c. A notochord is characteristic of chordates. d. A notochord serves to distinguish the Ediacaran fauna from the trilobites.

c. A notochord is characteristic of chordates.

What evidence did Darwin use to predict the age of Earth? a. Darwin didn't predict the age of Earth. b. Darwin used mathematical formulas to calculate the age of the Earth. c. Darwin used processes he could observe, such as erosion and sedimentation, to predict that Earth must be hundreds of million years old. d. It doesn't matter, because Lord Kelvin refuted Darwin's evidence.

c. Darwin used processes he could observe, such as erosion and sedimentation, to predict that Earth must be hundreds of million years old.

Which outcome would you predict if you compared the isotopes of fossils of two species of human ancestors and found high ratios of carbon-13: carbon-12 in one and low ratios in the other based on the illustration at the right? a. The species with low ratios likely ate grains from grasses or meat from animals that grazed on grasses. b. The species with low ratios likely ate a mixed diet containing berries, leaves, and tubers. c. The species with high ratios likely ate a mixed diet. d. It would depend on the type of human fossils.

c. The species with high ratios likely ate a mixed diet.

What is an isochron? a. The ratio of rubidium (Rb) to strontium (Sr). b. The rate of radioactive decay of an isotope. c. The slope of the line describing the ratio of 87Sr to 86Sr. d. A line on a graph of isotope ratios that indicates mineral samples formed at a similar time.

d. A line on a graph of isotope ratios that indicates mineral samples formed at a similar time.

How did scientists determine that Tyrannosaurus rex could not run very fast? a. They compared skeletal structures of Tyrannosaurus rex to modern animals to determine the size of T. rex's muscles. b. They used living animals to test a model they had developed on the biomechanics of running. c. They used evolutionary theory to determine the most closely related living organisms to T. rex. d. All of the above.

d. All of the above.

What allows us to know that synapsids were tetrapods? a. They lived on land. b. They were the dominant land animals. c. They evolved into mammals. d. They had four legs that they used for walking.

d. They had four legs that they used for walking.