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The History of Life on EarthChapter 8

Section 1: Evidence of the Past

Section 2: Eras of the Geologic Time Scale

Section 3: Humans and Other Primates


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Evidence of the PastSection 1

Bellringer

A mnemonic device is a trick that can help you remember words. Write down the four steps of natural selection. Then create a mnemonic device to help you remember each step by using the first letter of each step as the first letter of a word in a phrase that is easy for you to remember.

Write your answer in your science journal.



Objectives

• Explain how fossils can be formed and how their age can be estimated.

• Describe the geologic time scale and the way that scientists use it.

• Compare two ways that conditions for life on Earth have changed over time.


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Fossils

• Life Preserved in Rock Fossils are traces or imprints of living things—such as animals, plants, bacteria, and fungi—that are preserved in rock.


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The Age of Fossils

• Life Preserved in Rock Estimating the age of rocks and fossils based on its position in sedimentary rock is called relative dating. Absolute dating is a method that measures the age of fossils or rocks in years. The next slide shows how half-lives can be used to date fossils.

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Using Half-Lives to Date FossilsSection 1



The Geologic Time Scale

• Divisions of Time Paleontologists have divided the geologic time scale into large blocks of time.

• Mass Extinctions Some of the important divisions in the geologic time scale mark times when rapid changes happened on Earth. During these times, many species died out completely, or became extinct.


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The Changing Earth• Pangaea German scientist Alfred Wegener proposed that long ago the continents formed one landmass, which he called Pangaea, surrounded by a gigantic ocean.

• Do the Continents Move? In the mid-1960s, J. Tuzo Wilson of Canada came up with the idea that huge pieces of the Earth’s crust were pushed around by forces within the planet. His theory is illustrated on the next slide.

• Adaptations to Slow Change When conditions on the Earth change, organisms may adapt or become extinct.


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Moving Continents and Tectonic PlatesSection 1


Eras of the Geologic Time ScaleSection 2

Bellringer

Suppose that electrical energy was never developed. How would your life differ from what it is like now? What kinds of games and toys do you have that work without electricity? Do you think you would be miserable or would you still have plenty of ways to have fun?

Write your answers in your science journal.


Eras of the Geologic Time Scale Section 2

Objectives

• Outline the major developments that allowed life to exist on Earth.

• Describe the types of organisms that arose during the four major divisions of the geologic time scale.


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Precambrian Time


• How Did Life Begin? Scientists think that life developed from simple chemicals in the oceans and in the atmosphere.

• Photosynthesis and Oxygen The first cyanobacteria began to release oxygen gas into the oceans and air. Eventually, some of the oxygen formed a new layer of gas in the upper atmosphere.

• Multicellular Organisms After about 1 billion years, organisms that were larger and more complex than prokaryotes appeared in the fossil record.

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The Paleozoic Era


• When Was the Paleozoic Era? The Paleozoic era began about 543 million years ago and ended about 248 million years ago.

• Life on Land During the 300 million years of the Paleozoic era, plants, fungi, and air-breathing animals slowly colonized land.

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The Mesozoic Era


• Life in the Mesozoic Era Dinosaurs are the most well known reptiles that evolved during the Mesozoic era.

• The Extinction of Dinosaurs At the end of the Mesozoic era, 65 million years ago, dinosaurs and many other animal and plant species became extinct.

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The Cenozoic Era


• The Age of Mammals The Cenozoic era is sometimes called the Age of Mammals. Mammals have dominated the Cenozoic era the way reptiles dominated the Mesozoic era.

• The Cenozoic Era Today We are currently living in the Cenozoic era. Modern humans appeared during this era.

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Humans and Other PrimatesSection 3

Bellringer

Understanding evolution requires recognizingsimilarities and differences. What makes you uniqueamong your family members? What makes you recognizable as part of your family? Are all these traits physical or are some behavioral?

Write your answer in your science journal.



Objectives

• Describe three characteristics that all primates share.

• Describe three major groups of hominids.


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Primates


• The First Primates The ancestors of primates may have coexisted with the dinosaurs.

• Apes and Chimpanzees Scientists think that the chimpanzee, a type of ape, is the closest living relative of humans. A comparison of a human and ape skeleton is shown on the next slide.

• Hominids Humans are in a family separate from other primates. This family, called hominids, includes only humans and their human-like ancestors.

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A Comparison of Primate SkeletonsSection 3



Hominids Through Time• The Earliest Hominids The earliest hominids had traits that were more humanlike than apelike.

• Australopithecines Many early hominids are classified as australopithecines.

• A Variety of Early Hominids Some australopithecines had slender bodies. Some early hominids had large bodies and massive teeth and jaws.

• Global Hominids About 2.3 million years ago, a new group of hominids appeared. These new hominids were members of the group Homo.


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Recent Hominids• Neanderthals One recent hominid is known as Neanderthal. Neanderthals lived in Europe and western Asia.

• Early and Modern Humans Modern humans are classified as the species Homo sapiens. The earliest Homo sapiens existed in Africa 100,000 to 150,000 years ago.

• Drawing the Hominid Family Tree Scientists now speak of a “ tree” or even a “ bush” to describe the evolution of various hominids in the fossil record.


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The History of Life on EarthChapter 8

Concept Map


Use the following terms to complete the concept map on the next slide: geologic time scale, mammals, Mesozoic, paleontologists, Cenozoic, eukaryotes, relative dating, absolute dating, Paleozoic, dinosaurs, Precambrian.

Concept MapChapter 8


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