For approximately how many years have dinosaurs been extinct on Earth since their mass extinction at the end of the Cretaceous period?

Introduction / Context:
This question belongs to basic general knowledge about Earth history and prehistoric life. It asks when the non avian dinosaurs disappeared from the planet, which is closely linked to the well known mass extinction event at the boundary between the Cretaceous and Paleogene periods, commonly called the K T or K Pg extinction.

Given Data / Assumptions:

Dinosaurs dominated land ecosystems during the Mesozoic era. They became extinct in a major mass extinction event at the end of the Cretaceous period. The options list different approximate times in millions of years.

Concept / Approach:
Geologists and paleontologists use rock layers and radiometric dating to estimate when major events happened in Earth history. Evidence from many places on Earth shows a thin boundary layer rich in iridium and shocked minerals that marks the impact of a large asteroid and related volcanic and climate changes. This boundary marks the end of the Cretaceous period and the disappearance of non avian dinosaurs. The age of this boundary is about 66 million years before present, often rounded to about 65 million years in many school level general knowledge questions.

Step-by-Step Solution:
Step 1: Recall that the end Cretaceous extinction is dated to roughly 66 million years ago. Step 2: Notice that among the answer choices, the value closest to that scientific estimate is about 65 million years. Step 3: Recognize that numbers like 25 million years or 5 million years are far too recent, because already by that time mammals and birds had diversified greatly. Step 4: Values like 100 million or 135 million years would place the extinction in the middle of the Cretaceous or even earlier in the Mesozoic, long before dinosaurs actually vanished. Step 5: Therefore we choose the option that best reflects the accepted scientific figure, which is about 65 million years.

Verification / Alternative check:
You can cross check this with standard timelines taught in school. The Mesozoic era extends from about 252 million to 66 million years ago. The dinosaurs appear in the Triassic period and flourish during the Jurassic and Cretaceous periods. Their extinction is always placed at the Cretaceous end, so any approximate figure near 65 to 70 million years is consistent. Remembering that humans appear only in the last few million years shows immediately that figures like 5 or 25 million years are inconsistent with the long age of dinosaurs.

Why Other Options Are Wrong:
About 25 million years suggests a very recent extinction, but by that time mammals, whales and many modern groups already existed, and dinosaurs had long disappeared from the fossil record. About 100 million or 135 million years would cut off the dinosaurs in the middle of their era, which is not supported by fossils. About 5 million years is not even remotely correct, since many modern animals, including early humans, exist in that time frame and dinosaurs are absent from those sediments.

Common Pitfalls:
A common mistake is to mix up the ages of different geological events, such as confusing dinosaur extinction with the much earlier Permian extinction, or thinking in human timescales and severely underestimating the vast scale of geological time. Another pitfall is to memorize only the term K T extinction without linking it to an approximate number. To avoid this, associate dinosaurs with the number 65 or 66 million years, and remember that hominins appear roughly within the last few million years, which is much more recent.

Final Answer:
Dinosaurs have been extinct for approximately about 65 million years since their disappearance at the end of the Cretaceous period.