10.1 Origin of Life
• The earth was formed about 4.5 billion years ago.
• Scientists think that life began on earth about 3.5 billion years ago.
• Three ways life may have begun:
     1 - extraterrestrial origin
     2 - creation
     3 - origin from nonliving matter
• Miller & Urey showed that organic compounds can be formed from inorganic compounds under conditions that may have been present on the primitive earth.
• The first cells probably arose when membranes formed around aggregates of organic compounds.
10.2 Early Life in the Sea
• Bacteria are divided into 2 groups:
     eubacteria - modern bacteria and ancestors of mitochondria & chloroplasts
     archaebacteria - ancestors of eukaryotes
• About 3 billion years ago, cyanobacteria evolved and released oxygen into the oceans and air.
• About 1.5 billion years ago, the first eukaryotes (protists) evolved from bacteria.  Protists developed into more complex, multicellular life forms, such as plants, animals, and fungi.
• In the Cambrian period (600 to 500 million years ago) most major groups of animals evolved.
• In the history of the earth, there have been five mass extinctions where many species of organisms died off rapidly.
10.3 Invasions of the Land
• About 400 million years ago the ozone layer developed;  this allowed organisms to live on land.
• Mycorrhizae (a partnership between plants and fungi) allowed the first living things to move from water to land to live.
• Arthropods (especially insects) were the first animals to thrive on land.
10.4 Parade of Vertebrates
• Vertebrates are organisms that have a vertebral column or backbone.
• The first vertebrates were jawless fishes.
• Other vertebrate groups that evolved are: jawed fishes, sharks, bony fishes, amphibians, reptiles, birds, and mammals.
• Simpler vertebrates like fish, amphibians, and reptiles are ectotherms (cold-blooded).
• More complex vertebrates like birds and mammals are endotherms (warm-blooded).