According to geological and fossil evidence, for approximately how long has life existed on Earth?

Introduction / Context:
This question tests an important fact from geology and evolutionary biology. It asks about the age of life on Earth, not the age of Earth itself. Knowing the approximate time scale of life helps put evolution, fossil records, and planetary history into perspective.

Given Data / Assumptions:

• The options present values in millions and billions of years.
• Earth itself is about 4.5 billion years old.
• We are looking for the approximate time since the earliest known life forms appeared.

Concept / Approach:
Geological evidence from very ancient rocks and microfossils suggests that simple, single celled organisms existed on Earth as early as about 3.5 billion years ago. This makes 3.5 billion years the best approximate figure for how long life has existed. The distractor options of millions of years are far too small compared with the fossil record, while 35 billion years is older than the estimated age of the universe, so it is impossible.

Step-by-Step Solution:

Verification / Alternative check:
Standard school level textbooks and reliable science references state that the earliest evidence of life, in the form of microfossils and chemical signatures, dates back to roughly 3.5 to 3.8 billion years ago. This provides independent confirmation that the correct answer involves billions, not millions, of years and supports the figure given in option c.

Why Other Options Are Wrong:

• Option a, 3.5 million years, is wrong because it represents a time close to the evolution of some modern mammals and is far too recent for the origin of life.
• Option b, 35 million years, is wrong because it still represents only a small fraction of Earth history and does not match fossil evidence.
• Option d, 35 billion years, is wrong because it exceeds the age of the universe and is scientifically impossible.

Common Pitfalls:
Candidates sometimes confuse million with billion and may rush to pick a familiar looking number without checking the unit. To avoid this, always compare the options with known reference points, such as the age of Earth and the approximate age of the universe. Doing this quickly shows that only a figure in billions of years can be correct for the age of life.

Final Answer:
3.5 billion years