Chapter 25 (4)

From its beginnings, life on Earth has seen teh rise and fall of groups of organisms. __ originated, flourished and then diclined as the oxygen content of the atmosphere rose. Billions of years later, the first __ emerged fromt eh sea, giving rise to amphibians that went to dominate life on land for 100 mil years- until other __ replaced them as dominant terrestrial vertebrates. These and other major changes in life on Earth have been influeenced by large-scale processes such as __, __ and __.

The continents are part of great plates of Earth's crust that essentially float ont he hot, underlying portion of the __. Thes eplates move over time in a process called __. Geologists can measure rate of movement as well as past locations of the continents using the __ recorded in rocks at the time of their formation. This method works because as a continent shifts its position over time, the direction of magnetic north recorded in its newly formed rocks also changes.

many imp geologic processes, like mt and island formation, occur at __. in some cases, plates mvoe away form each other, like the __ and __ plates. In some, plates slide past each other, like the __. Last, others collide- oceanic plates are more dense than terrestrial plates. As a result, when an oceanic plat collides with a terrestrial plate, the oceanic plate usually sinks below it. WHen two oceanic plates or two terrestrial plates collide with one another, violent upheavals occur and mountains form along the plate boundairies. Ex: Himalayas- eurasian plate and Indian plate

TRUE OR FALSE:
- Plate movements rearrage geography slowly, but their cumulative effects are dramatic. Continental drift also has a major impact on life on earth.

__ alters the habitats in which organisms live. __ is the supercontinent in which alll landmasses were together by plate movements, meaning "all land." Ocean basins became deeper, which lowered sea level and drained shallow coastal seas. At that time, most marine species inhabited shalllow waters, and teh formation of __ destroyed a considerable amt of that habitat. The interior of the vast continent was cold and dry , prob an even more sever environment than that of central Asia today. Overall, teh formation of __ had a tremendous impact on the physical environment and climate, which drove some species to extinction and provided new opportunities for groups of organisms that survived the crisis.

Another effect of __ is teh climate change that results when a continent shifts northward or southward.

__ also promotes __ ona grand scale. When supercontinents break apart, regions that ocne were connected become geographically isolated. As the continetns drifted apart over the last 200 million years, each became a separate evolutionary arena, with lineages of plants and animals that diverged those on other continets.

Finally, __ can explain puzzles about the __ of extinct organisms.

The __ shows that the overwhelming majority of species that ever lived are now extinct. A species may becoe extinct for many reasons. Its habitat may have been destroyed, or its environment may have changed in a manner unfavorable to the species.

Even if physical factors in teh environment remain stable, __ may change- the origin of one species can spell doom for another.
Although extinction occurs on a regular basis, at certain times disruptive global environmental changes have caused the rate of extinctio to increase dramatically. When this occurs, a __ results in which large numbers of specie become extinct throughout Earth.

Five __ over 500 million years. Parti. well documented for decimation of hard-bodied animals living in shallow seas, organisms for which the __ is most complete. In each __, 50% or more of Earth's marine species became extinct.

Two mass extinctions- the __ and the __- have received the most attention. Te __ mass extinction, which defines the boundary betweent eh __ and __ eras (251 mil years ago) claimed about 96% of marine animal species and drastically altered life in the ocean. Terrestrial life also affected (8 of 27 orders of insects wiped out.) The mass extinction occurred in less than 5 million year, possibly in a few thousands of years- an instant int eh context of geologic time.

The __ occurred at the time of enormous volcanic eruptions in what is now Siberia. This period was the most extreme episode of __ to have occurred during the past half bil years. Geologic data indicate that an area of 1.6 mil km2 was covered with a layer of lava hundreds to thousands meters thick. Besides spewing enormous amts of lava and ash, the eruptions may have produced enough CO2 to warm the global climate by an estimated 6 degrees Celcius. Reduced temp differences between the equator and the poles would have slowed the mixing of ocean water, which in turn would have reduced the amt of oxygen available to marine organisms. This oxygen deficit may have been a major cause fo the _- extinction of marine life.

The __ mass extinction occurred about 65.5 mil years ago and marks the boundary betweent eh __ and __ eras. THis event extinguished more than half of all marine species and eliminated mayn families of terrestrial plants and animals including most of the dinosaurs.

__ is an element that is very rare on Earth but common in many of the meteorites and other extraterrestrial objects that occasionally fall to earth.

One clue to a pssible cause of the __ is a thin layer of clay enriched in iridium.

Human actions, like __, are modifying the global environment to such an eextent that many species are threatened with extinction. More than 1000 species have become extinct in the last 400 years. Scients estimate that this rate is 100 to 1000 times the typical backround rate seen in the __.

it is hard to document the total number of extinctions occurring today.It is clear that losses to date have not reached those fo teh big five __, in which large percentages of Earth's species became extinct.

By removing large numbers of species, a __ can reduce a thriving and complex ecological community to a pale shadow of its former self. In addition, when an evolutionary lineage disappears, it cannot reappear. THis changes the course of evolution forever.

__ shows that it typically takes 5-10 mil years for the diversity of life to recoer to previous levels after a __. In some cases, it has taken much longer than that: It took 100 mil years for the number of marine families to recover after the __ mass extinction. These data have sobering impications. If the current trends continue and a sixth __ occurs, it will take millions of years for life on Earth to recover.

__ can also alter ecolgical communities by changing the types of organisms found in them. For ex, after the __ and __, the percentage of marine organisms that were predators increased substantially. A rise int he number of predator species can increase both the pressures faced by prey and the competition among predators for food. In addition, __ can remove lineages with highly advantageous features.

The fossil record indicates that the diversity of life has increased over the past 250 mil years. This increas has been fueled by __, periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different __ in their communitites. Large scale __ occurred after each of the big five __, when survivros became adapted to the many vacant __. __ have also occurred in groups of organisms that possessed major evolutinary innovatiosn, sucha s seeds or armored body coverings, or that colonized regions in which they faced little comp from other species.

Fossil evidence indicates that mammals underwent a dramatic __ after the extinction of terrestrial dinosaurs 65.5 mil years ago. Although mammals originated about 180 mil years ago, the mammal fossils older than 65.5 mil years are mostly small and not morpholoically diverse.

Early mammals may have been restricted in size and diversity because they were eaten or outcompeted by the larger and more diverse dinosaurs. With the disappearance of hte dinosaurs, mammals expanded greatly in both diversity and size, filling the __ once occupied by terrestrial dinosaurs.

The istory of life has also been greatly altered by __ in which groups of organisms increased in diversity as they came to play eniterely new ecological roles in their communities. Each of these last three rradiations was associated with major evolutionary innovations that facilitated life on land. THe __ of land plants was associated with key adaptaitons, like stems tht support plants against gravity and a waxy coat that protects leaves from water loss. Finally, organissms that arise in an adaptive radiation can serve as a new source of food for still otehr organisms. In fact, the diversification of land plants stimulated a series of __ in insects that ate or pollinated plants, helping to make insects that ate or pollinated plants, helping to make insects the most diverse group of animals on Earth today.

Striking __ have also occurred over more limited geographic areas. SUch radiations can be initiated when a few organisms make their way to a new, often distant location in which they face relatively little competition from other organisms.

Each island was born naked and was gradually populated by stray organisms that rode the ocean currents and winds either from far-distant land areas or from older islands of the archipelago itself. THe physical diversity of each island, including immense variation in elevation and rainfuall, provides many opportunites for evolutionary divergence by __. Multiple invasions followed by __ events have ignited an explosion of __ in Hawaii. Most of the htousands of species that inhabit teh islands are ound nowhere else on Earht.