The History of Life and Earth

You can estimate quantitative data (fairly precisely) from a graph. The first step is to obtain a conversion factor by measuring along an axis that has a scale. In this case, 25 million years (my; from 60 to 35 million years ago (mya) on the x-axis) is represented by a distance of 7.0 cm. This yields a conversion factor (a ratio) of 25 my/7.0 cm = 3.6 my/cm. To estimate the time period represented by a horizontal bar on this graph, measure the length of that bar in centimeters and multiply that measurement by the conversion factor, 3.6 my/cm. For example, a bar that measures 1.1 cm on the graph represents a persistence time of 1.1 cm * 3.6 my/cm = 4 million years.

Your measurements indicate that a fossilized skull you unearthed has a carbon-14/carbon-12 ratio about 1 ⁄ 16 that of the skulls of present-day animals. What is the approximate age of the fossilized skull?

Calculate the mean (average) persistence times for species with planktonic larvae and species with nonplanktonic larvae.

Count the number of new species that form in each group beginning at 60 mya (the first three species in each group were present around 64 mya, the first time period sampled, so we don’t know when those species first appear in the fossil record).

Propose a hypothesis to explain the differences in longevity of snail species with planktonic and nonplanktonic larvae.

What hypothesis did Miller test in his classic experiment?

How would the appearance of protocells have represented a key step in the origin of life?

In changing from an “RNA world” to today’s “DNA world,” genetic information must have flowed from RNA to DNA. After reviewing Figures 17.4 and 19.9, suggest how this could have occurred. Does such a flow occur today?

Describe an example from the fossil record that shows how life has changed over time.

The first appearance of free oxygen in the atmosphere likely triggered a massive wave of extinctions among the prokaryotes of the time. Why?

What evidence supports the hypothesis that mitochondria preceded plastids in the evolution of eukaryotic cells?

What would a fossil record of life today look like?

Explain the consequences of plate tectonics for life on earth.

What factors promote adaptive radiations?

Suppose that an invertebrate species was lost in a mass extinction caused by a sudden catastrophic event. Would the last appearance of this species in the fossil record necessarily be close to when the extinction actually occurred? Would the answer to this question differ depending on whether the species was common (abundant and widespread) or rare? Explain.

Explain how new body forms can originate by heterochrony.

Why is it likely that Hox genes have played a major role in the evolution of novel morphological forms?

Given that changes in morphology are often caused by changes in the regulation of gene expression, predict whether noncoding DNA is likely to be affected by natural selection. See Concept 18.3 to review noncoding DNA and regulation of gene expression.

Fossilized stromatolites 

(A) formed around deep-sea vents. 

(B) resemble structures formed by bacterial communities that are found today in some shallow marine bays. 

(C) provide evidence that plants moved onto land in the company of fungi around 500 million years ago. 

(D) contain the first undisputed fossils of eukaryotes.

The oxygen revolution changed Earth's environment dramatically. Which of the following took advantage of the presence of free oxygen in the oceans and atmosphere?

(A) the evolution of cellular respiration, which used oxygen to help harvest energy from organic molecules 

(B) the persistence of some animal groups in anaerobic habitats 

(C) the evolution of photosynthetic pigments that protected early algae from the corrosive effects of oxygen 

(D) the evolution of chloroplasts after early protists incorporated photosynthetic cyanobacteria

Which factor most likely caused animals and plants in India to differ greatly from species in nearby southeast Asia?

(A) The species became separated by convergent evolution.

(B) The climates of the two regions are similar.

(C) India is in the process of separating from the rest of Asia.

(D) India was a separate continent until 45 million years ago.

Adaptive radiations can be a direct consequence of three of the following four factors. Select the exception. 

(A) vacant ecological niches 

(B) genetic drift 

(C) colonization of an isolated region that contains suitable habitat and few competitor species 

(D) evolutionary innovation

Which of the following steps has not yet been accomplished by scientists studying the origin of life? 

(A) synthesis of small RNA polymers by ribozymes 

(B) formation of molecular aggregates with selectively permeable membranes 

(C) formation of protocells that use DNA to direct the polymerization of amino acids

(D) abiotic synthesis of organic molecules.

A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of 

(A) the influence of environment on development. 

(B) paedomorphosis. 

(C) a change in a developmental gene or in its regulation that altered the spatial organization of body parts. 

(D) heterochrony

A swim bladder is a gas-filled sac that helps fish maintain buoyancy. The evolution of the swim bladder from the air-breathing organ (a simple lung) of an ancestral fish is an example of 

(A) exaptation. 

(B) changes in Hox gene expression. 

(C) paedomorphosis. 

(D) adaptive radiation

Describe how gene flow, genetic drift, and natural selection all can influence macroevolution.

Herbivory (plant eating) has evolved repeatedly in insects, typically from meat-eating or detritus-feeding ancestors (detritus is dead organic matter). Moths and butterflies, for example, eat plants, whereas their “sister group” (the insect group to which they are most closely related), the caddisflies, feed on animals, fungi, or detritus. As illustrated in the following phylogenetic tree, the combined moth/butterfly and caddisfly group shares a common ancestor with flies and fleas. Like caddisflies, flies and fleas are thought to have evolved from ancestors that did not eat plants. There are 140,000 species of moths and butterflies and 7,000 species of caddisflies. State a hypothesis about the impact of herbivory on adaptive radiations in insects. How could this hypothesis be tested?

WRITE ABOUT A THEME: Organization You have seen many examples of how form fits function at all levels of the biological hierarchy. However, we can imagine forms that would function better than some forms actually found in nature. For example, if the wings of a bird were not formed from its forelimbs, such a hypothetical bird could fly yet also hold objects with its forelimbs. In a short essay (100–150 words), use the concept of “evolution as tinkering” to explain why there are limits to the functionality of forms in nature.

In 2010, the Soufriere Hills volcano on the Caribbean island of Montserrat erupted violently, spewing huge clouds of ash and gases into the sky. Explain how the volcanic eruptions at the end of the Permian period and the formation of Pangaea, both of which occurred about 252 million years ago, set in motion events that altered evolutionary history.