WHAT KILLED THE DINOSAURS?

PART A

1 The Cretaceous is usually noted for being the last portion of the "Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first ceratopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants.

The breakup of the world-continent Pangaea, which began to disperse during the Jurassic, continued. This led to increased regional differences in floras and faunas between the northern and southern continents.

The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. This laid open the stage for those groups which had previously taken secondary roles to come to the forefront. The Cretaceous was thus the time in which life as it now exists on Earth came together.

2 Grazing mammals, such as members of the perissodactyl and artiodactyls diversified in the Miocene and Pliocene as grasslands and savanna spread across most continents.

The Pliocene was a time of global cooling after the warmer Miocene. The cooling and drying of the global environment may have contributed to the enormous spread of grasslands and savannas during this time. The change in vegetation undoubtedly was a major factor in the rise of long-legged grazers who came to live in these areas.

Additionally, the Panamanian land-bridge between North and South America appeared during the Pliocene, allowing migrations of plants and animals into new habitats. Of even greater impact was the accumulation of ice at the poles, which would lead to the extinction of most species living there, as well as the advance of glaciers and ice ages of the Late Pliocene and the following Pleistocene.

PART B

1

Volcanism:

Some scientists think the answer lies locked within the remnants of long-dormant volcanoes. Massive beds of ancient lava found around the world depict an earth 65 or 70 million years ago where volcanic eruptions were commonplace.

Mammal Competition:

Extinction implies that the species that perish are poorly adapted to a changing set of conditions.

Faced with an evolving group of competing organisms-the mammals- perhaps dinosaurs were driven to extinction by competition

Continental Drift:

It's difficult to imagine a process more gradual than continental drift. But some scientists say that, slow or not, this repositioning of the world's landmasses was disastrous for dinosaurs.

As continents heaved upward, pushed by the movement of tectonic plates, ocean currents were redirected and global sea levels fell. The Interior Seaway, for example, which once divided North America in half, simply drained away as the Colorado Plateau rose thousands of feet

Asteroid Impact:

It's widely agreed that such an object-10 kilometers across-struck just off the coast of the Yucatan peninsula 65 million years ago.

According to scientists who maintain that dinosaur extinction came quickly, the impact must have spelled the cataclysmic end.

2 Our group have choose the theory of de meteorite

There are a lot of theories about why this K-T (Cretaceous-Tertiary) extinction occurred, but a widely accepted theory (proposed in 1980 by physicist Luis Alvarez and his son Walter Alvarez, a geologist), is that an asteroid 4-9 miles (6-15 km) in diameter hit the Earth about 65 million years ago. The impact would have penetrated the Earth's crust, scattering dust and debris into the atmosphere, and causing huge fires (generated by hot debris thrown from the crater), tsunamis, severe storms with high windsand highly acidic rain, seismic activity, and perhaps even volcanic activity. The impact could have caused chemical changes in the Earth's atmosphere, increasing concentrations of sulfuric acid, nitric acid, and fluoride compounds. The heat from the impact's blast wave would have incinerated all the life forms in its path.

The dust and debris thrust into the atmosphere would have blocked most of the sunlight for months, and lowered the temperature globally.

Those organisms that could not adapt to the temperature and light changes would die out. Since plants' energy is derived from the sun, they would likely be the first to be affected by changes in climate. Many families of phytoplankton and plants would die out, and the Earth's oxygen levels may well have dramatically decreased, both on land and in the oceans, suffocating those organisms which were unable to cope with the lower oxygen levels.

Major changes in the food chain would result from all of these these environmental upheavals. The herbivores (plant eaters) who ate those plants would starve soon after the plants died. Then, at the top of the food chain, the carnivores (meat eaters), having lost their prey, would have to eat each other, and eventually die out. Their large carcasses must have provided smaller animals with food for quite a while.

LOCATION OF THE IMPACT CRATER

There are many impact craters on Earth. A 120-mile-wide (180 km), 1-mile-deep (1600 m) impact crater, Chicxulub, is found at the tip of the Yucatán Peninsula, in the Gulf of Mexico. This crater dates back to 65 million years ago, and is probably the site of the K-T meteorite impact. Evidence of K-T period tsunamis all around the Gulf of Mexico has been found.

The Shiva crater is a another huge impact crater located under the Arabian Sea off the coast of India near Bombay. This crater also dates from the K-T boundary, 65 million years ago, when the Chicxulub crater at the tip of the Yucatán Peninsula also formed. Although it has shifted because of sea floor spreading, when pieced together it would be about 370 miles (600 km) by 280 miles (450 km) across and 7.5 miles (12 km) deep (and may be just part of a larger crater). It is estimated to have been made by a bolide (an asteroid or meteoroid) 25 miles (40 km) in diameter. This crater was named by the paleontologist Sankar Chatterjee for Shiva, the Hindu god of destruction and renewal.