Dinosaurs dominated life on Earth for more than 150 million years. In fact, during their reign, other animal species had little chance of playing anything other than secondary roles to the dinosaurs. Then, 65 million years ago, they vanished. There are several hypotheses about the disappearance of these “great lizards.” Here are three:
Viewpoint #1 - Volcanism
Massive deposits of ancient lava found throughout the world depict an Earth 65- million-years ago where massive volcanic eruptions were common. Lava flows, like those found in the Deccan region of India, reveal a 500,000 year period of active volcanism; a time in which massive amounts of smoke and ash were projected into Earth’s atmosphere. This global volcanic activity prevented sunlight from reaching Earth’s surface. With the decrease in available sunlight, temperatures on Earth dropped significantly. Plant life dramatically declined and photosynthesis dropped sharply. Very few species could escape the effects of a darkened sky and the drastic loss of producers in food webs everywhere on Earth. Dinosaurs as well as many other species could not survive these harsh changes on Earth. In fact, 70% of life on Earth died at this time.
Viewpoint #2 – Impact theory
65-million-years ago, a 10-kilometer asteroid struck Earth near the Yucatan Peninsula. The force of the asteroid is estimated to have been equal to that of three hundred million atomic bombs. Earth’s atmosphere filled with gas and dust from the asteroid’s impact, as well as with ash and smoke from resulting forest fires. Temperatures on Earth, as well as available sunlight, dropped dramatically. Plant life died and, as a result of this, so did many other species on Earth. When the dust and ash settled greenhouse gases, released as a result of the asteroid impact, caused temperatures to rise much higher than the average temperatures of pre-impact Earth. This shift in climatic conditions eventually resulted in the extinction of over 70% of all the species once living on Earth.
Viewpoint #3 – Continental drift
Some scientists believe that the slow repositioning of Earth’s landmasses lead to the extinction of the dinosaurs. Convection currents within the Earth’s mantle caused landmasses to drift, collide, and eventually heave upward. Ocean currents were redirected and sea levels throughout the planet dropped. For example, the interior seaway, which once divided North America, drained away as the Colorado Plateau rose thousands of feet into the air. Without shallow seas like this one, climates became cooler and drier. Such climatic change resulted in new ecosystems that could not provide enough biomass to support dinosaur life.
Viewpoint #1 and Viewpoint #2 have an important premise in common. Both consider _________ a key determinant in the extinction of the dinosaurs on Earth.
A. one of Earth's ice ages
B. a massive impact to Earth
C. the decline in photosynthesis
D. the rise of other animal species