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 (H2O)

Carbon dioxide (CO2)

Sulfur dioxide (SO2)

Carbon monoxide (CO) Nitrogen (N2)

Hydrogen (H2)

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 extinctionK-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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