1.10.2 The Heterotroph Hypothesis: An Introduction

Question 1

studies of primitive earth

Answer 1

• based on the study of other planets and rock

Question 2

Alexander Oparin and J. B. S. Haldane

Answer 2

• hypothesized that the conditions of primitive Earth consisted of a reducing atmosphere, which is an appropriate atmosphere for the synthesis of carbon-containing molecules—the molecules of life.

Question 3

biotic

Answer 3

• living organisms in the environment

Question 4

abiotic

Answer 4

• nonliving environment

Question 5

reducing atmosphere

Answer 5

• was thought to have consisted primarily of methane (CH4), water vapor, and ammonia (NH3).

Question 6

oxidizing atmosphere

Answer 6

• contains high amounts of oxygen (O2). Oxygen is an
  oxidizing agent—it grabs electrons. An oxidizing atmosphere is not favorable for synthesizing organic molecules because grabbing electrons is not conducive to making bonds.
• The chemicals in a reducing atmosphere can act as reducing agents—they donate electrons. This characteristic allows for the synthesis of organic molecules because as electrons are donated, bonds can form.

Question 7

An abundance of __________ was absent from the Earth’s atmosphere four billion years ago.

Answer 7

• free oxygen

Question 8

the chemicals in a reducing atmosphere act as reducing agents by donating electrons

Answer 8

• true

Question 9

Evidence suggests that 4.5 billion years ago the atmosphere most likely consisted of

Answer 9

• CH4, H2O, CO2, N2, and NH3

Question 10

Who were the scientists responsible for proposing that primitive Earth’s atmosphere was reducing?

Answer 10

• Oparin and Haldane

Question 11

The Earth’s early atmosphere is thought to have primarily been a (an) ______________ atmosphere, which is conducive to the synthesis of the molecules that make up the building blocks of life.

Answer 11

• reducing

Question 12

Which of the following forms of energy was not available for chemical reactions on primitive earth?

Answer 12

• fossil fuel