Chapter 25: The History Of Life On Earth

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adaptive radiation

Back 1

Period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill vacant ecological roles in their communities.

Front 2

amino acid

Back 2

An organic molecule possessing both carboxyl and amino groups. Amino acids serve as the monomers of polypeptides.

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ammonite

Back 3

A member of a group of shelled cephalopods that were important marine predators for hundreds of millions of years until their extinction at the end of the Cretaceous period (65.5 mya).

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Cambrian explosion

Back 4

A relatively brief time in geologic history when large, hard-bodied forms of animals with most of the major body plans known today appeared in the fossil record. This burst of evolutionary change occurred about 535–525 million years ago.

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endosymbiosis

Back 5

A process in which a unicellular organism (the “host”) engulfs another cell, which lives within the host cell and ultimately becomes an organelle in the host cell

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geologic record

Back 6

The division of Earth’s history into time periods, grouped into three eons—Archaean, Proterozoic, and Phanerozoic—and further subdivided into eras, periods, and epochs.

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half-life

Back 7

The amount of time it takes for 50% of a sample of a radioactive isotope to decay.

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heterochrony

Back 8

Evolutionary change in the timing or rate of an organism’s development.

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macroevolution

Back 9

Evolutionary change above the species level, including the origin of a new group of organisms or a shift in the broad pattern of evolutionary change over a long period of time. Examples of macroevolutionary change include the appearance of major new features of organisms and the impact of mass extinctions on the diversity of life and its subsequent recovery.

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marsupial

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A mammal, such as a koala, kangaroo, or opossum, whose young complete their embryonic development inside a maternal pouch called the marsupium.

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mass extinction

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Period of time when global environmental changes lead to the elimination of a large number of species throughout Earth.

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paedomorphosis

Back 12

The retention in an adult organism of the juvenile features of its evolutionary ancestors.

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Pangaea

Back 13

The supercontinent that formed near the end of the Paleozoic era, when plate movements brought all the landmasses of Earth together.

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physiology

Back 14

The processes and functions of an organism and their study.

Front 15

protobiont

Back 15

A collection of abiotically produced molecules surrounded by a membrane or membrane-like structure.

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radioactive isotope

Back 16

An isotope (an atomic form of a chemical element) that is unstable

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radiometric dating

Back 17

A method for determining the absolute ages of rocks and fossils, based on the half-life of radioactive isotopes.

Front 18

ribozyme

Back 18

An RNA molecule that functions as an enzyme, catalyzing reactions during RNA splicing.

Front 19

serial endosymbiosis

Back 19

A hypothesis for the origin of eukaryotes consisting of a sequence of endosymbiotic events in which mitochondria, chloroplasts, and perhaps other cellular structures were derived from small prokaryotes that had been engulfed by larger cells.

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stromatolite

Back 20

Layered rock that results from the activities of prokaryotes that bind thin films of sediment together.

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hetero

Back 21

different (heterochrony: evolutionary changes in the timing or rate of development)

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macro

Back 22

large (macroevolution: long-term evolutionary change including the origin of novel designs, adaptive radiations, and mass extinctions)

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paedo

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child (paedomorphosis: the retention in the adult organism of the juvenile features of its evolutionary ancestors)

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proto

Back 24

first (protobionts: aggregates of abiotically produced molecules)

Front 25

stromato

Back 25

something spread out

Front 26

List the sequence of four stages that could have led to the origin of the first living cells.

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1.Abiotic synthesis of organic molecules.

2.Abiotic synthesis of macromolecules.

3.Spontaneous formation of protobionts.

4.Origin of self-replicating molecules, probably RNA that made inheritance and natural selection possible.

Front 27

Label the eons, eras, and the key events shown on clock analogy of Earth’s history.

Back 27

a.Achaean
b.Proterozoic
c.Phanerozoic
d.Paleozoic
e.Mesozoic
f.Cenozoic
g.Prokaryotes
h.Atmospheric oxygen
i.Single-cells eukaryotes
j.Multicellular eukaryotes
k.Animals
l.Colonization of land

Front 28

Describe three major processes that have influenced the changing diversity of life on Earth.

Back 28

1.Continental drift: when continents form on supercontinent, many habitats are destroyed or changes. As continents change latitude, their climates either warm or cool. The separation of continents creates major geographic separation events,
making possible allopatric speciations.

2.Indeed, continental drift helps explain much of biogeography.

3.Mass extinctions empty many ecological roles, which may then be exploited by species that survived extinction

4.Adaptive radiations are multiple speciation events that fill newly formed or newly emptied niches. Thus, adaptive radiations may follow mass extinctions, the colonization of new regions, or the evolution of novel adaptations.

Front 29

What genetic changes would most likely lead to the evolution of new morphological forms?

Back 29

New morphological forms may evolve as a result of mutations in developmental genes or changes in the regulation of such genes. Such changes may affect the rate or timing of development or the spatial arrangement of body parts (e.g., Hox genes).

Front 30

What hypothesis did Miller and Urey test in their famous experiment?

Back 30

The hypothesis that conditions on early Earth could have permitted the synthesis of organic molecules from inorganic ingredients.

Front 31

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

Back 31

In contrast to random mingling of molecules in an open solution, segregation of molecular systems by membranes could concentrate organic molecules, assisting biochemical reactions.

Front 32

If scientists built a protobionts with self replicating RNA and metabolism under conditions similar to those on early Earth, would this prove that life began as in the experiment? Explain.

Back 32

No. Such a result would only show that life could have begun as in the experiment.

Front 33

Your measurement 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?

Back 33

22,920 years (four half lives: 5,730 x 4)

Front 34

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

Back 34

The fossil record shows that different groups of organisms dominated life on Earth at different points in time and that many organisms once alive are now extinct; specific examples of these points can be found in Figure 25.4. The fossil record also indicates that new groups of organisms can arise via the gradual modification of previously existing organisms, as illustrated by fossils that document the origin.

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Suppose researchers discover a fossil of an organism that lived 300 million years ago, but had mammalian teeth and a mammalian jaw hinge. What inference might you draw from this fossil about the origin of mammals and the evolution of novel skeletal structures? Explain.

Back 35

The discovery of such a (hypothetical) fossil organism would indicate that aspects of our current understanding of the origin of mammals are not correct because mammals are thought to have originated much more recently (see Figure 25.6). For example, such a discovery could suggest that the dates of previous fossil discoveries are not correct or that the lineages shown in Figure 25.6 shared features with mammals but were not their direct ancestors. Such a discovery would also suggest that radical changes in multiple aspects of the skeletal structure of organisms could arise suddenly - an idea that is not supported by the known fossil record.

Front 36

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

Back 36

Free oxygen attacks chemical bonds and can inhibit enzymes and damage cells.

Front 37

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

Back 37

All eukaryotes have mitochondria or remnants of these organelles, but not all eukaryotes have plastids.

Front 38

What would a fossil record of life today look like?

Back 38

A fossil record of life today would include many organisms with hard body parts (such as vertebrates and many marines invertebrates), but might not include some species we are very familiar with, such as those that have small geographic ranges and/or small population sizes (for example, all five rhinoceros species).

Front 39

Explain consequences of continental drift for life on Earth.

Back 39

Continental drift alters the physical geography and climate of Earth, as well as the extent to which organisms are geographically isolated. Because these factors affect extinction and speciation rates, continental drift has a major impact on life on earth.

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What factors promote adaptive radiations?

Back 40

Mass extinctions; major evolutionary innovations, the diversification of another group of organisms (which can provide new sources of food); migration to new locations where few competitor species exist.

Front 41

If a mass extinction were caused by a single, catastrophic event (such as an asteroid impact), what pattern would you expect regarding the dates when formerly common species lost in the extinction are last observed in the fossil record?

Back 41

Their fossils should be present right up to the time of the catastrophic event, and then disappear. Reality is a bit more complicated because the fossil record is not perfect. So the most recent fossil for a species might be a million years before the mass extinction, even if the species did not become extinct until the mass extinction.

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1. How can heterochrony cause the evolution of different body forms?

Back 42

Heterochrony can cause a variety of morphological changes. For example, if the onset of sexual maturity changes, a retention of juvenile characteristics (paedomorphosis) may result. Paedomorphosis can be caused by small genetic changes that result in large changes in morphology, as seen in the axolotl salamander.