Assertion (A): Fossils provide evidence that evolution of life forms has taken place on earth.
Reason (R): Fossils are remains of hard parts of life-forms found in rocks, and studying them in different sedimentary layers helps determine the geological period in which they existed.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both Assertion (A) and Reason (R) are correct and R is the correct explanation of A.
Assertion (A): Fossils provide evidence that evolution of life forms has taken place on earth. — True. A says fossils are a source of evidence for evolution; this is called paleontological evidence.
Reason (R): Fossils are remains of hard parts of life-forms found in rocks, and studying them in different sedimentary layers helps determine the geological period in which they existed. — True. R tells us what fossils are and what the study of their layers reveals.
Why R explains A? Rock sediments form one over the other, so each layer belongs to a different period. When fossils from these layers are compared, they show that life-forms varied over time and that new forms arose at different times. This is how fossils become evidence of evolution, so R is the correct explanation of A.
NCERT Extract:
What are the Evidences for Evolution? – “Evidence that evolution of life forms has indeed taken place on earth has come from many quarters. Fossils are remains of hard parts of life-forms found in rocks. Rocks form sediments and a cross-section of earth’s crust indicates the arrangement of sediments one over the other during the long history of earth. … A study of fossils in different sedimentary layers indicates the geological period in which they existed. The study showed that life-forms varied over time and certain life forms are restricted to certain geological timespans. Hence, new forms of life have arisen at different times in the history of earth. All this is called paleontological evidence.”