It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species’ death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species.

The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species become extinct at the same time- a mass extinction. One of the best- known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when appropriately 95 percent of all species died. Mass extinction can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the ocean. Such a change would probably lead to a mass extinction. One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth’s orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species’ survival may have nothing to do with its ability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.

Which of the following is NOT mentioned in paragraph 1 as resulting from repid ecological change?

Câu hỏi liên quan

• All of the following are mentioned in the passage about supercells EXCEPT that they ________.

• It can be inferred from paragraph 3 that _______.

• The word “they” refers to ................

ZUNIA12

• According to the passage, the doers of education are .............

• According to paragraph 4, which of the following is the most fascinating to booklovers?

• It can be inferred from the passage that if a person remembers a piece of information for two days, this is probably ............

• It can be inferred from the passage that the author ....

• What two factors help protect the Earth from radiation?

• Which of the following statement is supported by the passage?

• The passage is organized by .....

• Merlin put wheels under his shoes in order to ..................

• The word "obscurity" could best be replaced by __________

• The word "they" in the 2^nd  paragraph refers to ..............

• What can we assume is NOT true about Middle Earth?

• According to the passage, who was the first person to use artificial refrigeration for a practical purpose?

• According to the passage, which of the following sentence is NOT true?

• Which of the following is not mentioned as the field where English is the main language?

• The word “hidden” in paragraph 1 is closest in meaning to ______.

• The word "derived" in line 13 is closest in meaning to ..............

• What does the writer’s brother do?