History of Biological Diversity 14.1 The History of Life

Section 14.1 Goals Objective 1:Sequence of events in fossilization Objective 2: Compare techniques for dating fossils Objective 3: Describe major events using the geologic time scale

Land Environments  Earth formed about 4.6 billion years ago.  Gravity pulled the densest elements to the center of the planet.  After about 500 million years, a solid crust formed on the surface.

Atmosphere  The gases that likely made up the atmosphere are those that were expelled by volcanoes.  Water vapor (H 2 O)  Carbon dioxide (CO 2 )  Sulfur dioxide (SO 2 )  Carbon monoxide (CO)  Nitrogen (N 2 )  Hydrogen (H 2 )

Clues in Rocks  Fossil - preserved evidence of an organism.  Most organisms decompose before they have a chance to become fossilized. Paleontologist – scientist who studies fossils

Fossil Formation 1.Organism dies 2.Buried in sedimentary rock – deposited by wind, water or volcanic ash 3.Organism dissolves and replaced with minerals

Objective 1:Sequence of events in fossilization 1.What are the 3 steps to fossil formation? – Organism dies – buried in sedimentary rock – Organism is replaced with minerals 2.Where do fossils form? – Sedimentary rock 3.What are 2 methods for determining the age of a fossil? – Relative dating and Radiometric dating

Dating fossils Relative dating - used to determine the age of rocks by comparing them with those in other layers.

Law of Superposition – the oldest layers of a rock are found at the bottom and the youngest layers of rock are found at the top of a formation, if the rock layers have not been disturbed

Radiometric Dating  Radiometric / Radioactive Dating - Uses the decay of radioactive isotopes to measure the age of a rock  Carbon-14 used for fossils  Uranium – 238 for rocks

Half-life – the amount of time required for half of a radioactive isotope to decay

Objective 2: Compare techniques for dating fossils 1.What fossil dating technique compares layers of rock? – Relative dating 2.Which fossil dating technique uses radioactive isotopes to measure the age of rocks? – Radioactive or radiometric dating 3.What is the time required for half of a radioactive sample to decay? – Half - life

The Geologic Time Scale  Geological time scale - a model that expresses the major geological and biological events in Earth’s history.  Era – a large division of geologic time scale  Eras are divided into one or more periods

Precambrian  The formation of Earth to the beginning of the Paleozoic era 542 million years ago  Autotrophic prokaryotes provided the atmosphere with oxygen.

The Paleozoic Era  Cambrian explosion – rapid diversification of most major animal groups during the Paleozoic era  Fish, land plants, and insects appeared during the Ordovician and Silurian periods.  The first tetrapods emerged in the Devonian.

 At the end of the Permian period, a mass extinction ended the Paleozoic era  Between 60 and 75 percent of the species alive went extinct.

The Mesozoic Era  Triassic period - Mammals and dinosaurs first appeared  Jurassic period- Birds evolved from dinosaurs  65 ma a meteorite struck Earth and caused a mass extinction  K-T boundry – layer of iridium found between the rocks of the Cretateous period and Paleogene period = evidence of meteorite impact

 Plate tectonics - Geologic theory that Earth’s surface is broken into several huge plates the move on a molten rock layer  These plates, some of which contain continents, move atop a partially molten layer of rock underneath them.

The Cenozoic Era  Mammals became the dominant land animals.  After the mass extinction at the end of the Mesozoic era, mammals of all kinds began to diversify.

Objective 3: Describe major events using the geologic time scale 1.What are the 2 major divisions of the geologic time scale? – Eras and Periods 2.What are the 3 major eras? – Paleozoic era, Mesozoic era, Cenozoic era 3.What provided early Earth with oxygen? – Autotropic prokaryotes

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