Correct Answer: Option 4 – extinction of the dinosaurs

The Cretaceous–Tertiary extinction event, which occurred approximately 65.5 million years ago, was a large-scale mass extinction of dinosaurs in a geologically short period of time. Widely known as the K–T extinction event, it is associated with a geological signature known as the K–T boundary, usually a thin band of sedimentation found in various parts of the world. K is the traditional abbreviation for the Cretaceous Period and T is the abbreviation for the Tertiary Period.

Correct Answer: Option 2

After the first half life only 50% of the radioactive isotope is available and the other 50% is the decay product. After the 2^nd half life the remaining radioactive isotope again halves. Hence, option 2 representing 25% of radioactive isotope and 75% of decay product is the correct answer.

Hence, the options 1, 3 and 4 representing varying proportions of the radioactive isotope and the decay product are incorrect.

Correct Answer: Option 1 - Cambrian

The Cambrian is the first geological period of the lasting from 542 million years ago

Incorrect Options

The Ordovician is a geologic period and system and covers the time between 488 to 443 million years ago

The Silurian is a geologic period and system and covers the time between 443 to 416 million years ago

The Triassic is a geologic period and system and covers the time between 251 to 199 million years ago.

Correct Answer: Option 4 – Seafloor bedrock is younger near the ridge and older farther away

Seafloor spreading occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge

Hence, the other observations in options 1, 2 and 3 are not providing inference for the above statement.

Correct Answer: Option 1 – under the ocean

This is the most appropriate answer by inspecting the nature of fossils (fish in layer 1 and sea shell in layer 8) which are characteristics of rock sedimentation under ocean.

This kind of fossils are not found in rock sedimentations formed from a desert, repeatedly covered by lava flows nor glaciated several times. Hence, options 2, 3 and 4 are incorrect.

Correct Answer: Option 3 – are members of the same group of organisms

These organisms have lived in the same environment and have shells. Hence, option3 is the correct answer.

Correct Answer: Option 3 – contain index fossils of the same age

Correct Answer: Option 4 – Ordovician

The Ordovician is a geologic period and system is the time between 488.3 and 443.7 million years ago

Early Ordovician time, gave way to fine-grained clastic deposition and deeper water conditions during the Middle Ordovician. Sometime during this period a convergent plate boundary developed along the eastern edge of a small island chain. Crustal material beneath the Iapetus Ocean sank into the mantle along a subduction zone with an eastward-dipping orientation.  The sedimentary and igneous rock between the land masses were intensely folded and faulted, and were subjected to varying degrees of intense metamorphism. This was the final episode of the long-lasting mountain-building period referred to as the Taconic Orogeny.

When the Taconic Orogeny subsided in the New York Bight region during Late Ordovician time (about 440 million years ago), subduction ended, culminating in the accretion of the Iapetus Terrane onto the eastern margin of the continent. This resulted in the formation of a great mountain range throughout New England and eastern Canada, and perhaps to a lesser degree, southward along the region that is now the Piedmont of eastern North America.