oldest fossils usually: _____.1. are found in the deepest strata 2. have the longest half-lives 3. are found in sediments formed during the Cenozoic era 4. contain more radioactive isotopes than younger fossils 5. are found above younger fossils

According to the law of superposition, the rocks that are found at the bottom of an undisturbed sedimentary sequence are the oldest rocks as these layers are initially formed due to the process of deposition, sedimentation and lithification, and with progressive sedimentation, the rock layers that are formed at the the apex portion are the youngest rocks.

So, the fossils found in bottom rocks are the oldest fossils, and those fossils that are found in the top layer are considered to be the youngest fossils.

Thus, the oldest fossils are the ones that are found in the deepest strata.

Therefore, the correct answer is option (1).