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Chapter 21 Fossils & the Rock Record. Major milestones in life Crawling, walking, potty training...
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Transcript of Chapter 21 Fossils & the Rock Record. Major milestones in life Crawling, walking, potty training...
Chapter 21
Fossils & the Rock Record
Major milestones in life• Crawling, walking, potty training (still in progress?), first day of school,
first kiss, first gf/bf, first love/break up, starting high school, driving a car, graduating, full-time job, parenting, retiring
Are there any categories into which these events can be placed?- Could include infancy, toddlerhood, childhood, adolescence,
adulthood
How do these categories help people communicate and analyze their life histories?- Not everyone reaches the same milestone at the same time. It is using to have references for communicating events
21.1 The Rock Record
Objectives Explain why scientists need a geologic time scale Distinguish among eons, eras, periods, and epochs Characterize the groups of plants and animals that dominated
eras in Earth’s history
Main Idea: Scientists organize geologic time to help them communicate about Earth’s history
Unknown vocab: fossil—the remains, trace, or imprint of a once-living plant or animal
Organizing TimeThese multicolored layers of rock are called strata• Some of these layers contain
fossils
By studying such rock layers and the fossils within them, geologists can reconstruct aspects of Earth’s history and interpret ancient environments
To help in the analysis of Earth’s rocks, geologists have divided history of Earth into time units• Based largely on the fossils contained within the rocks• Time units are part of the geologic time scale—a record of Earth’s history from its origin
(4.6 bya) to the present)
Some units have remain unchanged for centuries, while others have been reorganized based on new evidence
Geologists organize Earth’s history according to grouping called eons• Each eon contains era, which contain periods, which contain periods, which contain
epochs E + P = EP
Geologic Time Scale
Enables scientists to find relationships among geological events, env. conditions, and fossilized life-forms preserved in rock recordEons:• Largest of time units and contains all other units of time• Consist of Hadean, Archean, Proterozoic, and Phanerozoic
Eons• 3 earliest eons make up 90% of geologic time, known as
Precambrian During Precambrian, Earth was formed and became hospitable to modern life
Simple life-forms began in Archean Eon and that by end of Proterozoic Eon, life had evolved to point that some organisms might have been able to move in complex ways
Precambrian
Most fossils from this eon were soft-bodied organismsOthers had bodies with rigid partsAll life-forms had soft bodies without shells or skeletons
Era time units are defined by the different life forms found in the rocksSome periods are named for the geographic region in which the rocks or fossils characterizing the age were first observed and described
Eras, Periods, & Epochs
Eras All eons made up of eras—next largest unit of time• Usually tens to hundreds of millions of years
Periods All eras divided into periods• Generally tens of millions of years in duration
Epochs All periods are divided into epochs• Generally hundreds of thousands to millions of years in duration• Rocks & sediments from epochs of Cenozoic Era are most complete due to less time
for weathering & erosion to remove evidence
Succession of life-forms
During Phanerozoic Eon, multicellular life began to diversify• First era of this eon—Paleozoic—oceans became full of many different kinds of
organisms• Small, segmented animals called trilobites were among first hard-shelled life-forms• Dominated oceans in early part of Paleozoic Era• Land plants appeared later, followed by land animals
• End of Paleozoic is marked by largest mass extinction event in Earth’s history
• During a mass extinction, many groups of organism disappear from rock record at about same time
• At the end of the Paleozoic, 90% of all marine organisms became extinct
Conditions toward end of Paleozoic eraPangea had been in its final stages of formation• Conditions became dry on Pangea• Even though ocean covered most of Earth, Pangea was so big that the
interior did not benefit from the ocean waters • Swamp lands dried up—so many plants died out as well as amphibians
that depended on the swamps
other theories include • Increased volcanic activity• Comets/meteors
Whatever the cause, life on Earth would never again look as it had during the Paleozoic Era
Age of dinosaurs
Followed the Permian extinction Era known as the Mesozoic Large predatory reptiles and corals in the oceans also
appeared during this era Mammals continued to evolve and diversify Flowering plants & trees emerged as well End of the Mesozoic is marked by a large extinction that
eliminated many groups of organisms—including the non-avian dinosaurs and large marine reptiles
Rise of mammals
• Era the followed the Mesozoic—known as the Cenozoic
• Mammals increased in both number & diversity
• 1st primates, emerged in epoch called the Paleocene
• Modern humans appeared in the Pleistocene Epoch