History of Life (Ch. 19) The Fossil Record Fossils and Ancient Life Fossils are preserved remains or traces of ancient life. Fossils are the most important source of information about extinct species. An extinct species is one that has died out. Most fossils are preserved in sedimentary rock. Sediments build up over time, and bury the remains and traces of dead organisms. Scientists who study fossils are called paleontologists. What do fossils reveal about ancient life? • FOSSILS! – TRACE – MOLD – CAST – AMBER – IMPRINT – PETRIFIED Types of Fossils • A mold is an imprint of an organism or its trace. • A cast fossil forms when a mold fossil is filled with some form of mineral, usually through the seepage of water depositing the minerals within the mold. In time, the mold is filled and the materials deposited harden, creating a replica of the original fossil. This is called a cast fossil. • Trace fossils give us proof of animal life from the past. Trace fossils include things like foot prints, burrows, and fossilized poop. Types of Fossils • Amber - fossilized tree sap • The fossils that are encased in amber probably got there when they flew or crawled on to the fresh seeping sap and then got stuck. The sap oozed over the trapped animals and perhaps fell to the ground and was later covered by dirt and debris. The sap later hardened and became a fossil. Types of Fossils PETRIFIED • An exact stone copy of an organism, the hard parts of which have been penetrated and replace by minerals. Petrified Wood Fish fossil The Fossil Record Trilobite fossil Crayfish fossil Dinosaur footprint fossil Leaf fossil Conifer leaf fossil Dating Earth’s History Relative dating and radiometric dating are used to determine the age of fossils. •Relative dating establishes the relative age of fossils. Fossils from deeper rock layers are assumed to be older than fossils from rock layers closer to the surface. • Index fossils represent species that lived for a short period of time but over a wide geographic range. Index fossils can help determine the relative ages of rock layers and their fossils. • WHERE ARE FOSSILS USUALLY FOUND? • WHO STUDIES THESE? • HOW DO SCIENTISTS DETERMINE THE AGE OF SOMETHING BILLIONS OF YEARS OLD? – RELATIVE DATING – RADIOMETRIC DATING Dating Earth’s History • Radiometric dating determines a fossil’s approximate age in years by finding the proportion of radioactive to nonreactive isotopes in a sample. • Radioactive isotopes in fossils and rock layers decay, or break down, at a steady rate, called a half-life. • A half-life is the length of time needed for half of the radioactive atoms in a sample to decay. • A fossil’s age is calculated from the half-life and the amount of remaining radioactive atoms the fossil contains. Geologic Time Scale • The geologic time scale is a time line of Earth’s history based on relative and absolute dating. •The scale begins with the Precambrian. •Geologic time is divided into four eons: 1. Hadean 2. Archean 3. Proterozoic 4.Phanerozoic. GEOLOGICAL TIME • Too old for years or months • Four eras depending on which organisms lived • Precambrian • Paleozoic • Mesozoic • Cenozoic WHY DO WE HAVE DIFFERENT ERA’S? PRECAMBRIAN • WHAT DO SCIENTISTS THINK WAS ALIVE WAY BACK THEN?? • BACTERIA • THIS ERA LASTED FOR BILLIONS OF YEARS UNTIL MORE LIVING ORGANISMS EVOLVED PALEOZOIC ERA 540 MILLION YEARS AGO!! • • • • • • • • NOW THE EARTH IS GETTING LARGER LIFE! FIRST PART OF PALEOZOIC IS CALLED CAMBRIAN PROTISTS! SEA PLANTS! SEA ANIMALS! LAND PLANTS! LAND ANIMALS! WHAT ENDED THE PALEOZOIC ERA?? • MASS EXTINCTION! PALEOZOIC ERA 540 MILLION YEARS AGO MESOZOIC ERA 245 MILLION YEARS AGO!! • • • • • • • • DINOSAURS REPTILES SMALL MAMMALS APPEAR BIRDS EVOLVE PLATE TECTONICS WHAT ENDED THE MESOZOIC ERA? MASS EXTINCTION! ? METERORITE???? CENOZOIC ERA 66 MILLION YEARS AGO! • MAMMALS FLOURISH • PRIMATES ABOUT 30 MILLION YEARS AGO • MODERN HUMAN SPECIES – ABOUT 200,000 YEARS AGO Life on a Changing Planet • Climactic, geological, astronomical, and biological processes have affected the history of life on Earth. • Earth’s climate has changed often in the course of its history. • Small temperature shifts can bring about heat waves and ice ages which have great effects on living things. • Plate tectonics is a theory that Earth’s outermost layer is divided into plates that move. – The movement, called continental drift, has transformed life on Earth through the formation of mountain ranges, super continents, and other geologic features. Super Continent - Pangea Pangea - 250 million years ago After the break up - 65 million years ago Life on a Changing Planet • The impact of objects from space has affected the global climate. Patterns and Processes of Evolution (19.2) Speciation and Extinction • Macroevolutionary patterns are grand transformations in anatomy, phylogeny, ecology, and behavior that usually take place in clades larger than a single species. Speciation and Extinction A clade is a group consisting of an organism and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". Speciation and Extinction • If the rate of speciation in a clade is equal to or greater than the rate of extinction, the clade will continue to exist. • If the rate of extinction in a clade is greater than the rate of speciation, the entire clade will eventually become extinct. Speciation and Extinction • Background extinction is extinction caused by the slow process of natural selection. • Mass extinctions affect huge numbers of species over a relatively short time. This graph shows how the rate of extinction has changed over time. Rate of Evolution • Evidence shows that evolution has occurred at different rates for different organisms at different times. • The idea that evolution occurs slowly and gradually is called gradualism. • In punctuated equilibrium, long periods of little or no change are interrupted by short periods of rapid change. Gradualism • Supports Darwin’s theory Punctuated equilibrium • Gradualism does not always hold true. • Example – Horseshoe crabs have had very little change in structure from the time they appeared in the fossil record • These organisms are in a state of equilibrium. • Something happens to upset the equilibrium and rapid change occurs. – Punctuated equilibrium Rapid Evolution After Equilibrium – Rapid evolution may occur after a small population becomes isolated from the main population. This small population can evolve faster than the larger one because genetic changes spread more quickly among fewer individuals. – Rapid evolution may also occur when a small group of organisms migrates to a new environment. That’s what happened with the Galápagos finches. Adaptive Radiation • Adaptive radiation is the process in which a single species evolves into diverse species that live in different ways. This diagram shows part of the adaptive radiation of mammals. Adaptive Radiations in the Fossil Record – Dinosaurs flourished for about 150 million years during the Mesozoic Era. The fossil record documents that during this time, mammals diversified but remained small. – After most dinosaurs became extinct, however, an adaptive radiation began and produced the great diversity of mammals of the Cenozoic Era. Divergence / Adaptive Radiation • Divergence occurs when species evolve in several directions away from a common ancestor. This happens usually to fill a vacant ecological niche. Also known as adaptive radiation. Modern Adaptive Radiations – Both Galápagos finches and Hawaiian honeycreepers evolved from a single bird species. – Both finches and honeycreepers evolved different beaks and different behaviors that enable each of them to eat different kinds of food. Convergent Evolution – Sometimes groups of organisms evolve in different places or at different times, but in similar environments. – These organisms start out with different structures, but they face similar selection pressures. – In these situations, natural selection may mold different body structures in ways that perform similar functions. Because they perform similar functions, these body structures may look similar. – Evolution produces similar structures and characteristics in distantly-related organisms through the process of convergent evolution. Convergent evolution has occurred often in both plants and animals. Convergent Evolution – Mammals that feed on ants and termites evolved four times in four different regions. – They all developed the powerful front claws, long hairless snout, and tongue covered with sticky saliva that are necessary adaptations for hunting and eating insects. Coevolution – Sometimes, the life histories of two or more species are so closely connected that they evolve together. – The process by which two species evolve in response to changes in each other over time is called coevolution. Flowers and Pollinators – Coevolution of flowers and pollinators is common and can lead to unusual results. –For example, Darwin discovered an orchid whose flowers had 40-centimeter–About 40ayears later, long structurediscovered called a spur researchers with a supply nectar at the a moth with of a 40bottom. Darwin predicted centimeter-long feeding that some tube thatpollinating matched insect must have some kind of Darwin’s prediction. feeding structure that would allow it to reach the nectar. Darwin never saw that Plants and Herbivorous Insects – Plants and herbivorous insects also demonstrate close coevolutionary relationships. – Over time, many plants have evolved badtasting or poisonous compounds that discourage insects from eating them. Plants and Herbivorous Insects – Once plants began to produce poisons, natural selection on herbivorous insects favored any variants that could alter, inactivate, or eliminate those poisons. – Milkweed plants, for example, produce toxic chemicals. But monarch caterpillars not only can tolerate this toxin, they also can store it in their body tissues to use as a defense against their predators. • • • • • • Natural Selection : The Peppered Moth The peppered moth is a species of moth which uses camouflage against tree bark to avoid being eaten by birds. It is normally a light grey color. During England's industrial revolution, pollution caused a darkening of the bark of the trees. There was a natural variation in moth coloration with some being darker than others. Those moths of a lighter color, were easier to spot and eat by birds. And were eaten at a faster rate. The survivors tended to be darker, and when they mated, their offspring tended thus to be darker also. Over time, this resulted in the species becoming darker in color.