Final answer:
Animal life would quickly succumb to suffocation if green plants and algae were destroyed, as they are the planet's primary oxygen producers through photosynthesis.
Step-by-step explanation:
If a catastrophe were to destroy all green plants and algae on land and in water, the animal life on Earth would face severe oxygen depletion.
Green plants and algae are primary producers that generate oxygen as a by-product of photosynthesis. Without these organisms, the atmospheric oxygen levels would decline rapidly, affecting all aerobic organisms that depend on it for survival.
It is challenging to provide an exact timeframe for suffocation due to lack of oxygen, as it would depend on various factors like the size of the oxygen reservoir in the atmosphere, the rate of oxygen consumption by aerobic organisms, and the distribution of these organisms around the globe.
However, considering the oxygen cycle's complexity and the intricate balance of ecosystems, it is expected that such a catastrophic event would lead to the suffocation of animal life relatively quickly, potentially within a few years to a few decades.
The role of cyanobacteria in the oxygenation of Earth's atmosphere is pivotal.
These early phototrophic organisms transformed an anoxic environment into an oxygen-rich one, enabling the rise of more complex life forms.
If cyanobacteria and other phototrophs were eliminated, the lack of oxygen production would reverse this monumental evolutionary step, likely leading to the end of most aerobic life on Earth.