What is thought to have caused the mass extinction at the end of the cretaceous period? a) global warming eliminate b) an asteroid hitting earth in mexico c) extensive volcanic activity world-wide d) the start of glaciation and climatic changes

The answer is B. Geology has shown a thin layer of iridium (a rare mineral on earth but found on asteroids and meteors) in the rock layers between the Cretaceous and Paleogene periods. Below this layer are numerous fossils of  pterosaurs and dinosaurs, but above the layer are drastically few. The aftermath of asteroid impact is believed to have smothered most vegetation from earth which dinosaurs depended on as a source of food.  

a- multicellular

b-eukaryotic

c-no cell wall

d-heterotrophic

e-autotrophic

satellites are frequently used to make observations of the orbit on earth