History of Life on Earth

Laws of Evolution Evolution is a very slow process that brings about changes in living organisms Occurs randomly & selectively: 1. Genes mutate: changes in individual 2. Changes screened by natural selection - If changes offer advantage, helps to survive, changes transmitted to next generation. IF NOT THEN DISAPPEAR

Natural Selection A process that occurs naturally within a species. It results in the reproduction of organisms with traits that allow them to survive better in their environment. Evolution has lead to emergence of millions of species (see p. 308-309)

Early Life -Very little oxygen, so first living organisms were bacteria (photosynthesis!) - as oxygen accumulated in atmosphere organisms developed traits to breathe in air

2. Life multiplied in water, but living animals slowly developed traits to live on land Ex. Fins to limbs, and lungs lead to amphibians (water and land) 3. Living organisms adapted to climate changes. Ex. Ice ages

Geological Time Scale Began 4.6 billion years ago (Earth forms!) Geological time scale: a tool that represents the main divisions in the history of the Earth, based on the major events that have occurred in the history of life.

Four Eras Precambrian- began 4.6 billion years ago Paleozoic – began 543 million years ago Mesozoic – began 245 million years ago Cenozoic – began 65 million years ago See text book p. 312-313

Extinction: The disappearance of all individuals belonging to that species. It is caused by the inability of the individual to adapt to change (s) in their environment. 5 Mass Extinctions: involved the disappearance of numerous species in a short period of time. Permian Mass Extinctions: - 225 MYA (Paleozoic to Mesozoic) most devastating on Earth (90% marine life, & 70 % land species extinct - continental drift caused major volcanic eruptions - enormous amount of carbon dioxide was produced causing global warming - could have been caused by large meteor 50 km diameter

Cretaceous Extinction: - 65 MYA - 50 % of marine species and many plants and animals disappear (dinosaurs!) -caused by impact with a 10 km diam. Asteroid which released dust into the atmosphere that blocked the Sun. - the climate cooled, less photosynthesis for plants

Origin of Our Species Humans and Monkeys are both primates Human evolution diverged from great apes several million years ago - Human move on two feet (bipedalism) while chimpanzees & other apes seldom do!

Human Lineage 3 Main Genera: - Australopithecus (short & small skull) - Paranthropus (bigger & taller than Aust., & robust skull and teeth) - HOMO - Homo neanderthalensis- SHARED Europe, Asia, and Africa with our species - disappeared 30 000 years ago - Homo florensiensis – lived on Indonesian island of Flores - became extinct 12 000 years ago after a volcanic eruptions - Homo Sapiens (appeared 195 00 years ago, only survivor)

Homo Sapiens Our traits that make us different: 1. Bipedalism: free hands to make tools , clothes etc. 2. Fine Hair and more sweat glands to keep us cool 3. Large complex brain for superior mental capabilities Ex. Inventive, meet wants and needs, communicate using complex languages

Comparison of Skulls