Unit 1 NOS/Evolution ppt #6 Evolution: Early Earth History Photo credit: Jackie Beckett/American Museum of Natural History Copyright Pearson Prentice Hall

Earth is about 4.6 Billion years old!! Fossil records tell the Earth’s story. Over years many many layers of rock have formed. Many fossils are found within layers of rock. Fossils are the preserved remains or traces of organisms that lived in the past Copyright Pearson Prentice Hall

Interpreting Fossil Evidence Interpreting fossil evidence to show evolution or organisms Relative Dating Using the LAW of SUPERPOSITION: Rock layers form in order by age—the oldest on the bottom, with more recent layers on top. In relative dating, the age of a fossil is determined by comparing its placement to that of fossils in other layers of rock. Copyright Pearson Prentice Hall

Interpreting Fossil Evidence Relative Dating In relative dating, a paleontologist estimates a fossil’s age in comparison with that of other fossils. Each of these fossils is an index fossil. It enables scientists to date the rock layer in which it is found. Scientists can also use index fossils to date rocks from different locations. Photo credit: l. ©David Hanson/Stone; r. ©CORBIS Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall In Relative dating you are comparing 1 fossil to another, generating a history. For this you need an INDEX FOSSIL INDEX FOSSIL = An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range. Copyright Pearson Prentice Hall

Interpreting Fossil Evidence Interpreting Fossil Evidence to show evolution of organisms 2. Absolute Dating= radioactive dating Paleontologists determine the age of fossils using the fact that elements decay into measureable radioactive quantities. Scientists use radioactive decay to assign an absolute age to rocks Using radioactive decay, C12-C14scientists can determine true age of a fossil. Copyright Pearson Prentice Hall

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.

Interpreting Fossil Evidence By comparing the amounts of carbon-14 and carbon-12 in a fossil, researchers can determine when the organism lived. In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains. Copyright Pearson Prentice Hall

Compare/Contrast Table Section 17-1 Comparing Relative and Absolute Dating of Fossils Can determine Is performed by Drawbacks Relative Dating Absolute 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

Copyright Pearson Prentice Hall Geologic Time Scale Paleontologists use a scale called the geologic time scale to represent evolutionary time. It is time on the scale of the history of Earth, which spans 4.6 billion years Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide. Copyright Pearson Prentice Hall

Geological time scale shows macroevolution marked by mass extinctions and episodic speciation. Episodic speciation is a pattern of periodic large scale increase in new species that follows mass extinctions.

Compare/Contrast Table Section 17-1

Over Earth’s History, 99.9% of all species that have lived on Earth have become extinct, which means that the species has died out. Extinction means the death of an entire species.

Major Extinctions Precambrian Extinction: The abrupt and nearly complete disappearance of life form in late Precambrian may have resulted from unbalanced predation, grazing, or competition, or yet another environmental crisis such as supercontinent breakup, changes in ocean chemistry, and/or rising sea levels. Whatever the causes, most species disappeared by the end of the Precambrian, about 542 million years ago. Their extinction, however, appears to have paved the way for a spectacular evolution of much more familiar life, which marks the beginning of the modern Phanerozoic Eon: the Cambrian explosion.

Cambrian Explosion Cambrian explosion followed Precambrian extinction. The evidence shows that nearly all modern animal phyla, including our own chordate phylum, are represented in this diversity of life.

Major Extinctions Permian Extinction: During the Permian period, all the major landmasses of earth combined into a single supercontinent, Pangaea. During the formation of the supercontinent Pangaea, most marine invertebrate species disappeared with the loss of their coastal habitats. The Permian ended with the most massive extinction of all time; 99.5% of all species disappeared, opening the door for a new radiation of species in the Mesozoic.

Major Extinctions “K-T” (Cretaceous-Tertiary) Extinction: The dramatic extinction of all dinosaurs (except the lineage which led to birds) marked the end of the Cretaceous. A collision/explosion between the Earth and a comet or asteroid could have spread debris which set off tsunamis, altered the climate (including acid rain), and reduced sunlight 10-20%. A climatic shift to cooler temperatures because of diminished solar energy coincided with the extinction of dinosaurs. A consequent reduction in photosynthesis would have caused a drastic disruption in food chains. The massive extinction and sharp geologic line led geologists to define the end of the Mesozoic and the beginning of our modern Era, the Cenozoic, with this event.

Copyright Pearson Prentice Hall Formation of Earth Evolution of THE FIRST ORGANISMS… What substances made up Earth's early atmosphere? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Formation of Earth Earth's early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water. Copyright Pearson Prentice Hall

The Puzzle of Life's Origin Evidence suggests that 200–300 million years after Earth had liquid water, cells similar to modern bacteria were common. Copyright Pearson Prentice Hall

The Puzzle of Life's Origin Formation of Protocells  In certain conditions, large organic molecules like RNA form tiny bubbles called protocells. Protocells are not cells, but they have selectively permeable membranes and can store and release energy. Copyright Pearson Prentice Hall

The Puzzle of Life's Origin Hypotheses suggest that structures similar to protocells might have acquired more characteristics of living cells. Copyright Pearson Prentice Hall

The Puzzle of Life's Origin Evolution of RNA and DNA  How could DNA and RNA have evolved? Several hypotheses suggest: Some RNA sequences can help DNA replicate under the right conditions. Some RNA molecules can even grow and duplicate themselves suggesting RNA might have existed before DNA. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Free Oxygen About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans. Next, oxygen gas accumulated in the atmosphere. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Free Oxygen The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration. Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells The Endosymbiotic Theory The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Prokaryotes became the organelles within the Eukaryotic cell. Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells Endosymbiotic Theory Ancient Prokaryotes Chloroplast Plants and plantlike protists Aerobic bacteria Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Primitive Photosynthetic Eukaryote The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Animals, fungi, and non-plantlike protists Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells About 2 billion years ago, prokaryotic cells began evolving internal cell membranes. The result was the ancestor of all eukaryotic cells. According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several different prokaryotes. Eukaryotic, multicellular life evolved with sexual reproduction which increases genetic variability. Thus…evolution of higher life forms! Copyright Pearson Prentice Hall

Concept Map Evolution of first life Section 17-2 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 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.