
Concept explainers
Place the following events in Earth’s history in order. Which happened second?
a. Eukaryotes arose.
b. O2 gas accumulated in the atmosphere.
c. First multicellular organisms arose.
d. Prokaryotes arose.

Introduction:
The earth and other planets of the solar system formed around 4.6 billion years ago. The earth was a red-hot ball at that time and it slowly cooled down to form the crust. The earth cooled down further to allow the origin of first life form on earth. The changes in atmosphere of earth such as accumulation of oxygen took place gradually to allow origin of other life forms on earth.
Answer to Problem 1MCQ
Correct answer:
Accumulation of oxygen gas in the atmosphere is the second event to occur in the history of Earth. Therefore, option (b) is correct.
Explanation of Solution
Reason for the correct statement:
Prokaryotes arose around
Option (b) is given as “
As, “the accumulation of oxygen in the atmosphere constitute the second event to occur in Earth’s history in order”, is the right answer.
Hence, option (b) is correct.
Reasons for the incorrect statements:
Option (a), is given as “Eukaryotes arose”.
Eukaryotes arose around 1.5 billion years ago and this event is the third event in Earth’s history in order. Hence, it is a wrong answer.
Option (c), is given as “First multicellular organisms arose”.
First multicellular organism originated around 1.2 billion years ago and this event is the fourth event in Earth’s history in order. Hence, it is a wrong answer.
Option (d), is given as “Prokaryotes arose”.
The prokaryotes arose around
Hence, options (a), (c), and (d) are incorrect.
Accumulation of oxygen in the atmosphere is the second event to occur in the history of Earth.
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