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Origin of the Earth and of Life
Learning Objectives
After reading this chapter, students should be able to:
• Realize that the solar nebula formed from a cloud of interstellar gas
• Know that the Earth and the other terrestrial planets are 4.55 billion years old
• Know that the evidence for this age comes from radiometric dating of meteorites
• Understand how location in the solar nebula determined whether a planet became a
gas giant or a terrestrial planet.
• Understand that the moon was formed by a giant impact between the Earth and a
Mars-sized planetesimal
• Know how the early atmosphere and ocean formed from volatiles released from
impacts of comets and asteroids
• Realize that the Earth’s early atmosphere was drastically different from the present-
day atmosphere, with extremely low O2 and O3 levels and high CO2 levels.
• Know there are a number of theories on how life first arose, including a theory of
chemical evolution that results in an RNA-world.
• Know how the Urey-Miller experiment created amino acids, and what the
implications of this experiment were for the chemical evolution theory
• Realize that the gas mixture used in the Urey-Miller experiment probably does not
represent the atmosphere of the Earth when life first evolved
• Know what the RNA-world is and realize that many biologists support such a world
as a stepping stone towards the development of life because of RNA’s ability to self
replicate and encode protein production
• Consider the possibilities for prebiotic synthesis of glucose, and the RNA bases
• Consider theories for the evolution of life that involve prebiotic chemistry at
hydrothermal vents and in space
• Know that that most scientists agree that life had arisen by at least 3.5 billion years
ago, and that some believe life arose as early as 4.0 billion years ago
• Know what the Universal Tree of Life is, and its implications for the origin of life
• Offer multiple hypotheses explaining why methanogens are thought to be amongst
the earliest forms of life on Earth
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Review Questions
1.) How old is the solar system, and how is this age determined?
2.) How is the age of Earth determined if no rocks older than 4.1 billion years old
have been preserved?
3.) How do Jupiter and the Moon affect the habitability of Earth?
Jupiter occasionally perturbs asteroids into Earth-crossing orbits, decreasing the
habitability of Earth. However, Jupiter also acts to shield Earth from comets that
are perturbed from the outer solar system. Jupiter’s large gravity well can
4.) How and when did the atmosphere and ocean form? Which gases are thought to
have been present in the early atmosphere?
The atmosphere and oceans formed during the first 700 million years of the
5.) In what types of environments might life have originated?
Life could have originated on mineral surfaces near hydrothermal vents, where
lots of prebiotic chemistry could have taken place. Alternatively, life could have
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6.) Why is RNA thought to have preceded DNA in evolution?
7.) How is the Universal Tree of Life constructed?
8.) Into what three different domains are modern organisms divided?
Archaea, Eukarya, and Bacteria
9.) List two possible reasons why organisms near the base of the Tree of Life are
hyperthermophilic.
1 – The first organisms formed near hydrothermal vents and were
Critical-Thinking Problems
Write a 1 to 2 page, typed essay on the following question:
1.) What do you feel is the best theory for how life originated? Do you think that life
might exist elsewhere besides Earth?
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This is a thought question – we do not yet know how life originated or if life exists
outside of the Earth’s biosphere. Many scientists have dedicated their careers to
Resource Guide
Videos/Films:
Biology & Space Exploration Series: Episode I, “The Origin and Early Evolution of Life”
NASA TV
It Came From Outer Space VHS
Discovery Channel
www.discovery.com
This video discusses the possibility that life on Earth did not originate on Earth. This
theory, called panspermia, claims that life evolved on Mars first and then spread to Earth
via a meteor released during an impact event. (52 minutes)
The Earth and the Moon
Films for the Humanities and Sciences
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configuration as the Earth and the Moon. Original BBC broadcast title: A World Apart.
(50 minutes, color)
Intimate Strangers: Unseen Life on Earth, Episode 1. The Tree of Life
Annenberg/CPB
Dating the Earth
Films for the Humanities and Sciences
Websites:
Internet Resource Guide for astrobiology