Fossils can be formed …… B2 Old and new species: decay; isolated; asteroid; oxygen; minerals; soft; millions; competitors; natural; rocks; warmth; diseases; interbreeding; extinction; evolved; predators; billion; geological; variation; Using fossils Scientists cannot be certain about how life on earth began 3-4 billion years ago because… a) Early life forms were soft-bodied, so few became fossils. b) Most early fossils have been destroyed by geological activity. By comparing fossils of different ages and living organisms, scientists can see how much or little organisms have evolved. Fossils Fossils are the remains of organisms from many (often, millions) of years ago, often found in rocks. Fossils can be formed …… 1. From hard parts of animals that do not decay. 2. From parts of animals that did not decay due to a lack of oxygen, warmth or moisture. 3. When parts of an organism are replaced by other materials (such as rock minerals) as they decay. 4. From preserved traces of organisms eg footprints. Speciation (formation of new species) (HTonly) Two populations of the same species get isolated (eg mountains) Genetic variation exists in each population. Natural selection occurs in each population and the most successful alleles and characteristics allow survival. Each population becomes so different that interbreeding between them is not possible. Extinction The permanent loss of all members of a species from the planet is termed extinction. Causes of extinction include. 1. New predators 2. New diseases 3. New, more successful competitors 4. Asteroid collisions/massive volcanic eruptions 5. Changes to the environment