Read the passage given below and answer the four questions that follow:-
Microorganisms were discovered in tiny cracks within 2-billion-year-old rock in South Africa, making it the oldest rock known to host life. This finding offers insights into Earth's early life and the search for extraterrestrial life.
Deep within Earth's crust, billions of resilient microbes survive in extreme isolation, far removed from sunlight, oxygen, and food sources, growing at a glacial pace over thousands or millions of years. Previously, the oldest microbial traces were found in 100- million-year-old seafloor sediments. However, Yohey Suzuki and his team at Tokyo University have pushed this record back by 2 billion years.
They extracted a 30-cm cylindrical rock core from the Bushveld Igneous Complex in South Africa, a 2-billion-year-old volcanic region. Upon slicing the core, they found microbial cells in tiny fractures. DNA staining and imaging with advanced microscopes confirmed the microbes were indigenous, with intact cell walls, suggesting they were active.
The researchers hypothesise that the microorganisms were carried into the rock via water shortly after its formation. Clay deposits in the fractures may have provided nutrients. These microbes, primitive in evolutionary terms, offer clues about Earth's earliest life forms and their evolution.
The study also has implications for Mars exploration. Suzuki notes similarities between the Bushveld rocks and Martian rocks, suggesting the same techniques could identify life on Mars.
"This underscores the deep subsurface as a crucial environment for microbial life," says Manuel Reinhardt from the University of Göttingen, while noting that microorganisms colonised the rocks after crack formation; the timing needs investigation.
Why are the microbes described as "primitive in evolutionary terms"?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → They resemble Earth's earliest life forms in terms of adaptation.
The passage says these microbes, "primitive in evolutionary terms, offer clues about Earth's earliest life forms and their evolution." They are called primitive because they are close to the earliest forms of life, surviving in the same simple way, without sunlight, oxygen or a regular food supply.
Why the Other Options are Incorrect?
Option 1: They evolved from Martian microorganisms. — Incorrect. Not mentioned: Mars comes up only as a place where similar techniques could be used; the passage never says the microbes came from Mars.
Option 2: They lack DNA and structural complexity. — Incorrect. Contradicted: the researchers stained their DNA and found intact cell walls, so the microbes do have DNA.
Option 4: They were found in relatively young volcanic sediments. — Incorrect. Contradicted: they were found in 2-billion-year-old rock, the oldest known to host life, not in young sediments.