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

• Which of the following is TRUE according to the passage?

• Which of the following would most likely NOT be reflected in a person's costume, as it is defined in the passage?

• What does the word “magni” stand for?

ZUNIA12

• How would the author probably characterize the people who are mentioned in the first line of the second paragraph?

• It can be inferred from the passage that the author believes that business operated by women are small because ................

• All of the following are TRUE about long – term memory EXCEPT that ..........

• The expression day-to-day could best be replaced by which of the following?

• The word “it” in the second paragraph refers to ________.

• What do pads help the players to protect?

• What does the passage mainly discuss?

• Which of the following would NOT be a problem for the construction plan?

• It can be inferred from the passage that Walt Whitman________.

• The Pilgrims immigrated to the New World because ..............

• Which one of the statements doesn’t refer to smallpox?

• According to the passage, cellphones are especially popular with young people because ______.

• Which would be the most appropriate headline for the article?

• What is the main topic of the passage?

• What is the author’s main purpose in the first paragraph of to passage?

• What can the word adorning be best replaced by?

• The phrase "weary of" is closest in meaning to ...............