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Chapter 13: Problem 4

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. How did the atmosphere change during the first 2 billion years of Earth history? When did most continental crust form? (B)

Short Answer

Expert verified
During the first 2 billion years of Earth's history, the atmosphere evolved from being dominated by hydrogen and helium to a secondary atmosphere rich in water vapor, carbon dioxide, and nitrogen gases. The rise of oxygen in the Earth's atmosphere, known as the Great Oxidation Event, occurred around 2.4 billion years ago due to the emergence of photosynthetic bacteria and plants. Most of Earth's continental crust formed during the Mid-Archean to Proterozoic period, between 2.5 to 1.8 billion years ago.

Step by step solution

01

Understanding Earth's early atmosphere

In order to answer the first question, we should briefly discuss the early Earth's atmosphere, which was very different from today's. The early atmosphere, during the first billion years of Earth's history, consisted mainly of hydrogen and helium, but as the Earth cooled, these lighter gases escaped into space.
02

Formation of the secondary atmosphere

Over time, the Earth's secondary atmosphere began to form. This new atmosphere was mainly composed of water vapor, carbon dioxide, and nitrogen. Volcanic activity contributed significantly to this new atmosphere, releasing various gases like water vapor, carbon dioxide, sulfur dioxide, and nitrogen gases. This stage of development occurred during the first 2 billion years of Earth history.
03

The role of life on Earth in atmospheric changes

Life on Earth also played a key role in changing the composition of the Earth's atmosphere, especially due to the emergence of photosynthetic bacteria and plants. The process of photosynthesis led to the production of oxygen, which increased the oxygen content of the atmosphere. The rise of oxygen in the Earth's atmosphere is called the Great Oxidation Event and took place around 2.4 billion years ago.
04

Answering the first question

To summarize the answer to the first question, during the first 2 billion years of Earth history, the Earth's atmosphere underwent significant changes. It evolved from a hydrogen and helium dominated atmosphere to a secondary atmosphere rich in water vapor, carbon dioxide, and nitrogen gases. Lifeforms, particularly the emergence of photosynthetic organisms, also played a crucial role in changing the atmosphere, leading to the rise of oxygen.
05

Formation of Earth's continental crust

In order to answer the second question, we need to discuss the formation of Earth's continental crust. The Earth's crust is made up of two main types: oceanic and continental crust. Earth's continental crust began forming in the early stages of Earth's history. However, its growth was slow, and most of the continental crust that we see today formed during the middle part of Earth history, between 2.5 and 1.8 billion years ago.
06

Answering the second question

To answer the second question, most of Earth's continental crust formed during a period known as the Mid-Archean to Proterozoic, around 2.5 to 1.8 billion years ago. This is when the growth of the continental crust accelerated, leading to the formation of most of the continental mass we see today.

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Most popular questions from this chapter

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe the plate-tectonic conditions that led to the formation of the Sierran are and the Sevier fold-thrust belt. How does the Laramide deformation differ from the Sevier deformation in the United States? (C)

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Why did the Himalayas and the Alps form? (F)

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. How did the Alleghanian and Ancestral Rockies orogenies affect North America? (F)

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. When in Earth history did vascular plants appear? When did trees appear? (E)

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Did supercontinents exist in the Proterozoic? (F)
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