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Evolution. The History of Life. Early history of Earth. Earth is thought to have formed about 4.6 billion years ago. It began as a hot ball of rock. Meteorites bombarded its surface. Volcanoes shook the planet & shot out gases that formed an atmosphere. Early history of Earth.
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Early history of Earth • Earth is thought to have formed about 4.6 billion years ago. • It began as a hot ball of rock. • Meteorites bombarded its surface. • Volcanoes shook the planet & shot out gases that formed an atmosphere.
Early history of Earth About 3.9 billion years ago, the Earth cooled enough for water vapor to condense. Violent rainstorms occurred & the oceans formed. About 3.5 billion years ago, the first living organisms appeared.
Fossils • Oldest rocks are about 3.9 billions years old. • Fossils • Any evidence of an organism that lived long ago.
Paleontologists • Scientists who study ancient life
Relative dating technique • Based on the premise that the deeper an organism is buried in sediment, the older it is.
Radiometric dating technique • Involves using radioactive isotopes that give off radiation and form a different element. • Scientists determine the ages of rocks/fossils by comparing the amount of the original radioactive element to the amount of the new element formed from decay.
Radiometric dating technique • Example: K-40 (potassium-40) decays to form Are-40 (Argon-40) in 1.3 billion years.
Geologic time scale • A type of calendar that allows scientists to communicate about events that have occurred since Earth was formed. • Based on the different types of living organisms that have appeared during Earth’s history.
Geologic time scale • The scale is divided into 4 eras: • Precambrian • Paleozoic • Mesozoic • Cenozoic • These 4 eras are then subdivided into periods.
Precambrian era • Contains the oldest evidence of life (around 3.5 billion years old). • Prokaryotes & simple eukaryotic organisms (algae, sponges & jellyfish).
Paleozoic era • Invertebrates (worms & primitive arthropods) • Fishes (earliest vertebrates) • Plants • Amphibians • Reptiles
Mesozoic era • Dinosaurs • Mammals • Flowering plants
Cenozoic era • Mammals flourished. • Primates evolved.
Spontaneous generation • The idea that life was produced from nonliving matter.
Francisco Reid • In 1668, he disproved the theory of spontaneous generation of larger organisms. • People still believed that microorganisms arose spontaneously from a vital force in the air (“air theory”).
Louis Pasteur • In the mid-1800s, he disproved the “air theory” and established the concept of biogenesis.
Biogenesis • The idea that living organisms come only from other living organisms.
Alexander Oaring • In the 1930s, he hypothesized that life began in the early oceans. • He suggested that energy from the sun and lightning triggered chemical reactions with the primitive atmosphere. The products rained down into the oceans to form “primordial soup.”
Evolution of cells • First forms of life were anaerobic, heterotrophic prokaryotes, which probably evolved from some type of protocell. • Competition for nutrients by heterotrophic prokaryotes led to the evolution of the first autotrophs (similar to archaebacteria).
Evolution of cells • Photosynthesizing prokaryotes evolved next, which increased the oxygen concentration in Earth’s atmosphere. • Aerobic respiration evolved with the increase of oxygen.
Charles Darwin • English scientist who is considered the founder of modern evolutionary theory. • In 1831, he sailed on the HMS Beagle to South America & the South Pacific. • On the Galapagos Islands, Darwin studied & compared the anatomy of many organisms.
Charles Darwin • Darwin used his theory of natural selection to explain how organisms evolve.
Natural selection • A mechanism for change in populations that occurs when organisms with favorable variations for a particular environment survive, reproduce and pass these variations on to the next generation.
Natural selection • Those with less favorable variations are less likely to survive and pass on traits to the next generation. • Each new generation is largely made up of offspring from parents with the most favorable variations.
Natural selection • Natural selection is also known as “the survival of the fittest.”
Evidence for evolution • The following provide evidence for evolution: • Fossils • Anatomical studies • Embryological development • Biochemistry
Fossil evidence • Scientists use fossil records to understand the general pathway of evolution. A model of evolution from small-toed to one-toed horses.
Anatomical studies • A homologous structure is a modified structure that is seen among different groups of descendents.
Anatomical studies • An analogous structure is any body part that is similar in function but different in structure. • Example: Insect and bird wings have the same function but are not similar in structure (bird wings are made up of a set of bones while insect wings are mainly made of chitin).
Anatomical studies • A vestigial structure is any body structure that is reduced in function in a living organism but may have been used in an ancestor. Pelvic bones of a baleen whale.
Embryological development • In the earliest stage of embryological development in a fish, reptile, bird and mammal, a tail and gill slits can be seen in all species. • As development continues, the embryos become more & more distinct, & in the stages before birth, they attain their distinctive forms.
Biochemistry • Scientists use DNA, RNA and proteins to determine levels of relationships among species within major taxonomic groups.
Types of selection • Natural selection acts upon the variation in populations. • There are 3 types of selection: • Stabilizing selection • Directional selection • Disruptive selection
Stabilizing selection • The type of natural selection that favors average individuals in a population. • Large spiders are at a disadvantage b/c they can be seen & captured more easily. • Small spiders might not be able to catch enough prey to survive & reproduce. • Average-size spiders are “just right.”
Directional selection • When one of the extreme forms of a trait is favored by natural selection. • Woodpeckers feed by pecking holes in trees to get insects that live under the bark. • One year, the trees are invaded by a species of insect that lives deep within the trees. • Woodpeckers with long beaks have the selective advantage over those with short or average-size beaks.
Disruptive selection • Individuals with either of 2 extreme forms of a trait are at a selective advantage. • Limpets are shell-covered marine organisms that live attached to rocks. • On light-colored rocks, white-shelled limpets are able to blend in with the rock. • On dark-colored rocks, dark-colored limpets are able to blend in with the rock. • Tan-colored limpets, the intermediate forms, are easily spotted on either color rock.
Speciation • It is the process by which a new species is formed. • This can only occur when either interbreeding or the production of fertile offspring is somehow prevented. • Isolation can cause speciation.
