Arrange the following events in the history of life on earth in the order in which they took place:
A. The dinosaurs suddenly disappeared from the earth.
B. The first cellular forms of life appeared on earth.
C. Some land reptiles went back into water to evolve into fish-like reptiles such as Ichthyosaurs.
D. Invertebrates were formed and were active.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → B, D, C, A
NCERT gives a rough time for each of these events, counted in million years ago (mya). The bigger the number, the earlier the event, so arrange them from the largest figure to the smallest.
B. The first cellular forms of life appeared on earth. — First, about 2000 mya. Before this, life existed only as non-cellular giant molecules.
D. Invertebrates were formed and were active. — Second, by about 500 mya, after single-celled organisms had slowly become multicellular.
C. Some land reptiles went back into water to evolve into fish-like reptiles such as Ichthyosaurs. — Third, probably about 200 mya, in the long age when reptiles dominated the earth.
A. The dinosaurs suddenly disappeared from the earth. — Last, about 65 mya. The true reason is not known; climatic change is one of the suggestions.
NCERT Extract:
A Brief Account of Evolution – “… About 2000 million years ago (mya) the first cellular forms of life appeared on earth.”
A Brief Account of Evolution – “… Slowly single-celled organisms became multi-cellular life forms. By the time of 500 mya, invertebrates were formed and active. Jawless fish probably evolved around 350 mya.”
A Brief Account of Evolution – “… Some of these land reptiles went back into water to evolve into fish like reptiles probably 200 mya (e.g. Ichthyosaurs). The land reptiles were, of course, the dinosaurs. The biggest of them, i.e., Tyrannosaurus rex was about 20 feet in height and had huge fearsome dagger like teeth. About 65 mya, the dinosaurs suddenly disappeared from the earth.”