Download 19.3 Earth`s Early History

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Class
Date
19.3 Earth’s Early History
Lesson Objectives
Identify some of the hypotheses about early Earth and the origin of life.
Explain the endosymbiotic theory.
Explain the significance of sexual reproduction in evolution.
Lesson Summary
The Mysteries of Life’s Origins Earth’s early atmosphere contained toxic gases. The
atmosphere also contained little or no oxygen.
In the 1950s, Stanley Miller and Harold Urey set out to determine if organic molecules
mol
could assemble under early
ly E
Earth
arth conditions. They filled a container with water and gases
that they thought represented the composition of Earth’s early atmosphere. They passed
electric sparks through the mixture to simulate lightning. Soon, organic compounds
formed. The experiment showed
howed that molecules needed for life could have arisen from
simpler compounds.
Under some conditions, large organic molecules form tiny bubbles called proteinoid
microspheres. Structures similar to proteinoid microspheres might have become the first
livingg cells. RNA and DNA also could have evolved from simple organic molecules.
The first known life forms evolved about 3.5 billion years ago. They were single celled
and looked like modern bacteria. Eventually, photosynthetic bacteria became common.
During photosynthesis, the bacteria produced oxygen. The oxygen accumulated in the
atmosphere. The rise of oxygen drove some life forms to extinction. At the same time,
other life forms evolved that depended on oxygen.
Origin of Eukaryotic Cells The first eukaryotes, or organisms with nuclei, evolved from
prokaryotes that began to develop internal cell membranes. One explanation for how
eukaryotes evolved is the endosymbiotic theory. This theory proposes that smaller
prokaryotes began living insidee larger cells and evolved a symbiotic relationship with the
larger cells.
Sexual Reproduction and Multicellularity Sexual reproduction evolved after
eukaryotic cells. Sexual reproduction increased genetic variation, so evolution could occur
more quickly. Several hundred million years after sexual reproduction evolved, multicellular
life evolved.
BUILD Vocabulary
A. The chart below shows the key term in this lesson with its definition. Complete the chart by
writing a LATIN / GREEK strategy to help you remember the meaning of the term.
Word
Latin & Greek strategy
Endosymbiosis
BUILD Understanding
Flowchart A flowchart is a way to show a sequence of events. You can make a flowchart by
writing the steps in a series of connected boxes.
As you read Lesson 3, complete the flowchart
owchart to show the major steps from the origin of
Earth to the evolution of eukaryotic cells.
Earth forms.
Organic
molecules
form.
RNA and
DNA evolve.
The Mysteries of Life’s Origins
Scientists have as many questions as answers about the origins of life on Earth. The study of life’s
origins is a branch of scientific research that is always changing. Scientists do know that early
Earth was a very different place than today’s Earth.
Follow the directions.
1. Fill in the chart with information about early Earth and today’s Earth. Use terms from the
box.
brown oceans
blue skies
pinkish-orange skies
blue oceans
no life
many different life forms
about 20% oxygen
little to no oxygen
Early Earth
Today’s Earth
Oceans
Skies
Atmosphere
Life
Each of the following statements is false. Rewrite the statements to make them true.
2. Oceans on early Earth were blue because they contained lots of dissolved iron.
3. The atmosphere on early Earth could support human life because there was no oxygen.
4. For millions of years, asteroids shook Earth’s crust.
5. Microspheres evolved from living cells.
6. The first cells on Earth were eukaryotic.
The Mysteries of Life’s Origins
Production of Free Oxygen Early Earth’s atmosphere was mostly a mixture of carbon
dioxide, water vapor, and nitrogen. There was little to no oxygen. Life as we know it today
developed because of the production of free oxygen.
A cause-and-effect chart is similar to a flowchart. It shows what the impact of a certain event
is. The event is the cause. The impact of the event is the effect. Many causes can also be effects.
Follow the directions.
7. Complete the cause-and-effect chart below. Use the sentences in the box.
Organisms that used oxygen for respiration evolved.
The first cells became extinct.
The oceans changed color from brown to blue.
The ozone layer formed and skies turned blue.
The iron oxide sank to the ocean floor.
Cause: Photosynthetic bacteria began
producing oxygen.
Cause/Effect: Oxygen combined
with iron in the oceans to form
iron oxide.
Cause/Effect: Oxygen
accumulated in the atmoshpere.
Cause/Effect:
Cause/Effect:
Effect:
Cause/Effect:
Effect:
Answer the questions using complete sentences.
8. What life process put oxygen into the atmosphere?
9. Why do you think the first cells became extinct?
Origin of Eukaryotic Cells
Endosymbiotic Theory The endosymbiotic theory explains the evolution of
eukaryotic cells. According to the theory, ancient prokaryotes developed a symbiotic
relationship with smaller prokaryotes that lived inside them. Some of these smaller
prokaryotes could use oxygen to make ATP. These aerobic prokaryotes evolved into
mitochondria. Others could perform photosynthesis. These evolved into chloroplasts.
The diagram below shows the stages in the endosymbiotic theory.
Follow the directions to finish the diagram.
10. Draw the final step in the endosymbiotic theory. Your drawing should show a primitive
eukaryotic cell that performed photosynthesis.
11. Label the chloroplast in your drawing.
Ancient Aerobic
Prokaryote
Ancient Anaerobic
Prokaryote
Nuclear envelope
evolving
Mitochondrion
Primitive Aerobic
Eukaryote
Ancient Photosynthetic
Prokaryote
Animals, fungi, and
non-plantlike protists
Plants and
plantlike protists
Primitive Photosynthetic Eukaryote
Answer the questions.
12. Animals evolved from primitive eukaryotic cells with which structure?
chloroplast
mitochondria
nucleus
13. What evidence shows that bacteria and organelles of living cells share a common ancestry?
___________________________________________________________________________
Use the diagram of the Miller-Urey
Urey experiment to answer Questions 14-16.
14. THINK VISUALLY
Label the diagram to show which part of Miller and Urey’s
apparatus simulated lightning storms on early Earth.
15. What was the purpose of Miller and Urey’s experiment?
16. Explain the results of the Miller
Miller-Urey experiment. What did these findings suggest?
Origin of Eukaryotic Cells
17. Explain the endosymbiotic theory IN YOUR OWN WORDS!
Sexual Reproduction and Multicellularity
18. How did sexual reproduction speed up the evolutionary process?
19. What is the most likely cause of the great amount of diversity currently seen in multicellular
life forms?
Apply the Big idea
20. Once DNA evolved, what could have caused it to become the primary means of transmitting
genetic information instead of RNA? (Hint: think about the structure of DNA & RNA)
RNA
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