Nearly 75% of plant and animal species on Earth, including all non-bird dinosaurs, went extinct during the Cretaceous-Paleogene (or Cretaceous-Tertiary) extinction event. Scientists have spent years speculating about what precipitated this extinction. Various hypotheses have been presented to account for the disappearance of these huge creatures. The prevailing theory is that a large asteroid collided with Earth and its impact raised a cloud of dust that prevented sunlight from reaching the planet's surface for many years. Temperatures fell rapidly, and without sunlight, much of the plant life on the planet's surface disappeared. Without warmth or food, the dinosaurs, as well as many other species, became extinct.
In support of this theory, scientists have found a thin layer of sediment in marine and terrestrial rocks that contains metals that are rare on Earth but abundant in asteroids. Additionally, a large crater was found in the Gulf of Mexico that must have been formed when an asteroid hit Earth at roughly the same time as the extinctions took place.
Amid the destruction was opportunity for evolution. There were countless vacated ecological niches and the surviving organisms rapidly adapted and developed in order to occupy these niches. It is believed that several of the mammals, including primates, that are alive today developed during this time.
If the preceding information is true, which of the following is the most likely explanation for the fact there is still life on Earth today?

A. Some forms of life were able to survive in spite of the lack of sunlight.


In order for some life forms to survive, they would have needed to have the ability to survive despite the conditions described in the passage. One ability would be to be able to survive without sunlight, choose (A). The dinosaurs went extinct; they did not hibernate, eliminate (B). As we know, sunlight is critical to the survival of plants, which use it for photosynthesis so eliminate (C). There must have been some food on the planet or else no organisms would have survived, so eliminate (D).

Visit our website for other GED topics now!