“They can be thought of as "factories" in the cell”.
Answer:
Due to presence at early days of the planet.
Explanation:
We only find the remains of single celled organisms in the oldest fossils because the single celled organisms are the organisms that were present in the early days of this planet. These single celled microbes were present about 3.7 billion years ago while on the other hand, the oldest rocks are only a little older i. e. 3.8 billion years so these single celled organisms are considered as oldest fossils on this planet.
I think the answer is oxygen, but not 100% sure
The brain's suprachiasmatic nucleus regulates the body's circadian rhythms. The suprachiasmatic nucleus is a minute region of the brain located in the hypothalamus above the optic chiasm, the circadian rhythm is the 24-hour cycle of organisms, related to sunlight and temperature.
