[2026] PTE Academic Reading - Fill in the Blanks (Dropdown)
Fill in the Blanks (Dropdown) #0134
Fill in the Blanks (Dropdown)
Fill in the Blanks (Dropdown)
Below is a text with blanks. Click on each blank, a list of choices will appear. Select the appropriate answer choice for each blank.
The Great Oxygenation Event, which occurred roughly 2.4 billion years ago, was a profound biological and chemical turning point for the planet. Before this period, the atmosphere was almost entirely devoid of oxygen and consisted primarily of gases like methane and carbon dioxide. The emergence of cyanobacteria, which produced oxygen through photosynthesis, eventually led to a rapid in atmospheric oxygen levels. This transition had consequences for the planet's existing anaerobic life forms, for whom oxygen was essentially a poison. Furthermore, the rise of oxygen reacted with atmospheric methane, causing a cooling effect that triggered a prolonged period of global . Despite these initial extinctions, the presence of oxygen eventually the evolution of complex multicellular organisms and more efficient metabolic pathways. Today, scientists analyze chemical signatures in ancient sedimentary rocks to the precise timing and scale of this planetary transformation.
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Highlights
ID:pt7259035705
Test No:#0134
Difficulty:Easy
Success Rate
10
Correct
5
Wrong
3 people solved this
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