Exam 15: A Brief History of Life on Earth

When did free oxygen appear on Earth and how did it become part of the atmosphere?

Few mammal species can survive in less than a 10% oxygen atmosphere.

Both fish and human beings belong to the phylum _____.

The oldest known bird,illustrated below,featuring many dinosaur characteristics,is called _____.

The essential evolutionary development that allowed reptiles to be free of the water was the _____ egg.

Natural Selection,in modern understanding,is always a process of slow changes.

Primitive,single-celled life forms without organized nuclei are termed _____.

The most ancient fossils are found in sediments that are _____ billion years old:

Animals with jointed legs are referred to as _____.

Flying insects,such as this dragonfly,were abundant by the _____ Period.

The first fish venturing onto land belonged to the group called _____.

The 20 carbon-based compounds that are the essential building blocks of all proteinsare _____.

Which of the following gases was NOT likely contained in Earth's primary atmosphere?

What is a trace fossil?

Throughout Earth's history,_____ has been a main source of the addition of water and gases in the atmosphere and oceans.