Questions & Answers

Life originated in which era-
A. Proterozoic
B. Mesozoic
C. Precambrian
D. Cenozoic

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Hint: A theory called the Big Bang theory seems to explain the origin of the universe. It says that after a single huge explosion which cannot be imagined in physical terms. According to the Big Bang theory, the universe is almost 20 billion years old. This theory says that the earth is approximately 4.5 billion years old. The first form of life that was acellular originated 4 billion years ago.

Complete answer: After the explosion that took place, the universe expanded and the temperature came down. Under the effect of gravitation, the gases condensed and then the galaxies were formed. Life appeared 500 years after the earth was formed, i.e., 4 billion years ago. This life was acellular type. The first cellular form of life appeared possibly around 2 billion years ago. An era is an abbreviated form of evoked response audiometry, which means a system of chronological notation computed from a particular date as its basis. There are five eras in biology-
1. Azoic- no life was there in this era.
2. Proterozoic- it consists of two periods: Cambrian and Ordovician, where jawless fishes dominated.
3. Paleozoic- includes four periods:
i. Silurian- age of invertebrates
ii. Devonian- age of fishes
iii. Carboniferous- age of amphibians
iv. Permian- amphibians dominated
4. Mesozoic- has three periods:
i. Triassic- the origin of reptiles
ii. Jurassic- age of reptiles
iii. Cretaceous- the extinction of dinosaurs
5. Cenozoic- has two periods:
i. Tertiary- age of mammals and aves
ii. Quaternary- age of humans
The Precambrian era is the earliest part of the history of the earth, it accounts for 88 percent of the total geologic time of earth. The Precambrian era is divided into five natural eons- accretion and differentiation, hadean, archean, transition, proterozoic. The origin of life took place in the Precambrian era.
Therefore, the correct option is (C).

Note: Precambrian is the largest span of time which starts from the origin of the earth to the start of the Cambrian period. This era is marked by the presence of different layers of sedimentary rocks. In this era, the first protozoa appear followed by the worms. And not much after that time, arthropods, mollusks, and fungi came into existence as shown by the fossils. By the end of this Precambrian era complex organisms like jellyfishes, shelled organisms, and other animals like sponges appeared.