OBSCURED and ISOLATED were hotly debated answers to a difficult “fossil” question that appeared on both the US and the International October 3, 2026, SATs.
The passage begins by introducing readers to Albertosaurus, a large carnivorous dinosaur that lived about 71 million years ago in what is now Alberta, Canada, The bipedal creature had powerful hand legs, a massive skull, and razor-sharp teeth, banana-shaped teeth.
Studies clearly show that iron is present throughout each of the dinosaur’s surviving fossilized teeth. The passage uses the key word “since” to explain that over millions of years abundant deposits of iron in the surrounding site have seeped into the fossilized teeth. This has OBSCURED or masked whether the iron came from the dinosaur’s tissue or from the surrounding soil.
It is important to remember that ISOLATED means separated, set apart, or detached. If the extra iron flooded the entire tooth from external sediment, the original distribution of iron was merged or overwhelmed by outside minerals and therefore NOT separated or set apart.
OBSCURED – hidden, masked, altered, or made unclear
ISOLATED – separated, set apart, or detached
APUSH BONUS EXAMPLE
The Fugitive Slave Act of 1850 allowed bounty hunters to legally track and capture freedom seekers anywhere in the country. Underground railroad “conductors” attempted to thwart the bounty hunters by building false walls, hidden cellar trapdoors, and secret compartments behind bookcases to keep freedom seekers OBSCURED during slave-catcher inspections.