The History of Life & the Origin of Species Georgia Performance Standards: SB5a: Trace the history of the theory of evolution. SB5 c: Explain how fossil and biochemical evidence support the theory of evolution. Essential Questions: Why are there species alive now that were not found in the past fossil record? Why is important to understand evolutionary theory? How does fossil and biochemical evidence support the evolutionary theory?

14–1 The Fossil Record  You can study life’s history by examining fossils. The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms have changed over time. Paleontologists are scientists who collect and study fossils.

Fossils can show: That life on Earth has changed over time. What past life forms were like and if they are extinct (the species died out) The structure of the organisms What they ate What ate them The environment in which they lived.

How Fossils Form Either the remains of the organism or some trace of its presence must be preserved. Most fossils form in sedimentary rock The quality of fossil preservation varies.

Formation of a Fossil Section 17-1 Dead organisms are buried by layers of sediment, which forms new rock. Water carries small rock particles to lakes and seas. The preserved remains may later be discovered and studied. Go to Section:

Interpreting Fossil Evidence Relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock use index fossils to compare the relative ages of fossils. Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils.

Interpreting Fossil Evidence Radioactive dating is the use of half-lives to determine the age of a sample. A half-life is the length of time required for half of the radioactive atoms in a sample to decay.     In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.

Compare/Contrast Table Section 17-1 Comparing Relative and Absolute Dating of Fossils Can determine Is performed by Drawbacks Relative Dating (Absolute Dating) Radioactive Dating Age of fossil with respect to another rock or fossil (that is, older or younger) Age of a fossil in years Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen Imprecision and limitations of age data Difficulty of radioassay laboratory methods Go to Section:

Geologic Time Scale Paleontologists use divisions of the geologic time scale to represent evolutionary time. After Precambrian Time, the basic divisions of the geologic time scale are eras and periods.

Geologic Time Scale Geologists divide the time between the Precambrian and the present into three eras. Paleozoic Era Mesozoic Era Cenozoic Era Eras are subdivided into periods, which range in length from tens of millions of years to less than two million years.

Geologic Time Scale with Key Events Section 17-3 Era Period Time (millions of years ago) Key Events Cenozoic Mesozoic Paleozoic Precambrian Time Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian 1.8–present 65–1.8 145–65 208–145 245–208 290–245 363–290 410–363 440–410 505–440 544–505 650–544 Glaciations; mammals increased; humans Mammals diversified; grasses Aquatic reptiles diversified; flowering plants; mass extinction Dinosaurs diversified; birds Dinosaurs; small mammals; cone-bearing plants Reptiles diversified; seed plants; mass extinction Reptiles; winged insects diversified; coal swamps Fishes diversified; land vertebrates (primitive amphibians) Land plants; land animals (arthropods) Aquatic arthropods; mollusks; vertebrates (jawless fishes) Marine invertebrates diversified; most animal phyla evolved Anaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life Go to Section:

Chapter 14 The History of Life

Chapter 14 The History of Life 14.1 Fossil Evidence of Change Plate tectonics describes the movement of several large plates that make up the surface of Earth. These plates, some of which contain continents, move atop a partially molten layer of rock underneath them.

Chapter 14 The History of Life

Concept Map Evolution of Life Section 17-2 Go to Section: Early Earth was hot; atmosphere contained poisonous gases. Earth cooled and oceans condensed. Simple organic molecules may have formed in the oceans.. Small sequences of RNA may have formed and replicated. First prokaryotes may have formed when RNA or DNA was enclosed in microspheres. Later prokaryotes were photosynthetic and produced oxygen. An oxygenated atmosphere capped by the ozone layer protected Earth. First eukaryotes may have been communities of prokaryotes. Multicellular eukaryotes evolved. Sexual reproduction increased genetic variability, hastening evolution. Go to Section:

Spontaneous generation is the idea that life arises from nonlife. Chapter 14 The History of Life 14.2 The Origin of Life Origins: Early Ideas Spontaneous generation is the idea that life arises from nonlife. Francesco Redi, an Italian scientist, tested the idea that flies arose spontaneously from rotting meat.

Chapter 14 The History of Life 14.2 The Origin of Life The theory of biogenesis states that only living organisms can produce other living organisms. Louis Pasteur designed an experiment to show that biogenesis was true even for microorganisms.

Simple organic molecule formation Chapter 14 The History of Life 14.2 The Origin of Life Origins: Modern Ideas Simple organic molecule formation The primordial soup hypothesis was an early hypothesis about the origin of life. Organic molecules could have been synthesized from simple reactions. UV light from the Sun and electric discharge in lightning might have been the primary energy sources.

Chapter 14 The History of Life 14.2 The Origin of Life Stanley Miller and Harold Urey were the first to show that simple organic molecules could be made from inorganic compounds. Later, scientists found that hydrogen cyanide could be formed from even simpler molecules in simulated early Earth environments.

Chapter 14 The History of Life

Life requires proteins. Chapter 14 The History of Life 14.2 The Origin of Life Making Proteins Life requires proteins. One possible mechanism for the formation of proteins would be if amino acids were bound to a clay particle.

Some RNA sequences appear to have changed very little through time. Chapter 14 The History of Life 14.2 The Origin of Life Genetic Code Some RNA sequences appear to have changed very little through time. Many biologists consider RNA to have been life’s first coding system. Other researchers have proposed that clay crystals could have provided an initial template for RNA replication.

Scientists hypothesize that the first cells were prokaryotes. Chapter 14 The History of Life 14.2 The Origin of Life Cellular Evolution Scientists hypothesize that the first cells were prokaryotes. Many scientists think that modern prokaryotes called archaea are the closest relatives of Earth’s first cells.

Photosynthesizing Prokaryotes Chapter 14 The History of Life 14.2 The Origin of Life Photosynthesizing Prokaryotes Archaea are autotrophic. They do not obtain their energy from the Sun. Archaea also do not need or produce oxygen.

Chapter 14 The History of Life 14.2 The Origin of Life Many scientists think that photosynthesizing prokaryotes evolved not long after the archaea. Prokaryotes, called cyanobacteria, have been found in rocks as old as 3.5 billion years.

The Endosymbiont Theory Chapter 14 The History of Life 14.2 The Origin of Life The Endosymbiont Theory The ancestors of eukaryotic cells lived in association with prokaryotic cells. The relationship between the cells became mutually beneficial, and the prokaryotic symbionts became organelles in eukaryotic cells. This theory explains the origin of chloroplasts and mitochondria.

Chapter 14 The History of Life 14.2 The Origin of Life

Another View of Endosymbiotic Theory

Checkpoint Questions: What can be learned from the fossil record? Which type of dating provides an absolute age for a given fossil? Describe how this is done. How are eras and periods related? Many more fossils have been found since Darwin’s day, allowing several gaps in the fossil record to be filled. How might this information make relative dating more accurate?