Relative Dating and Rock Age Determination

How do scientists determine that Earth is approximately 4.6 billion years old?

• Using absolute dating techniques on meteorites.

• By measuring the Earth's circumference.

• Through the study of ancient civilizations.

• By analyzing the age of the oldest rocks on the Moon.

Which method of finding the relative age of rocks do scientists often use?

• A sedimentary rock layer in its original position is older than the layers above it and younger than the layers below it.

• The age of a rock can be determined by measuring its radioactive isotopes.

• Fossils found in sedimentary layers are the only way to determine relative age.

• The color of the rock is a reliable indicator of its age.

What is absolute dating used for in geology?

• To measure the exact age of fossils and rock layers

• To determine the relative age of rock layers

• To identify the mineral composition of rocks

• To assess the environmental conditions of the past

What is an index fossil used for?

• To compare the ages of fossils

• To identify the species of a fossil

• To determine the color of a fossil

• To measure the size of a fossil

Identify the area that shows an unconformity in the rock layers.

• A. The bottom layer that is flat.

• B. The middle layer that is heaved up.

• C. The top layer that is eroded.

• D. The layer that is missing entirely.

Identify the layer and depositional environment of the ocean reptile.

• Layer 1: A volcanic environment

• Layer 2: An ocean environment

• Layer 3: A desert environment

• Layer 4: A glacial environment

What is the half-life of uranium particles used in the example?

• 500 million years

• 704 million years

• 1 billion years

• 300 million years

In the rock layer where fossil C is found, how old is the rock?

• 250 million years

• 350 million years

• 450 million years

• 550 million years

At the Ashfalls site, how do scientists use both relative and absolute dating to determine the age of fossils?

• A. By comparing the layers of volcanic ash, scientists can determine relative age based on the order of the layers and the fossils found in each layer. They can also figure the absolute age of the fossils through carbon dating. This means they find the half-life of the carbon in the fossils. Because scientists know the half-life of carbon, they can measure the amount of carbon left in the bones to get the absolute age.

• B. Scientists only use relative dating by examining the physical characteristics of the fossils without considering the layers of ash.

• C. Absolute dating is determined solely by the depth of the fossils in the ground, while relative dating is ignored.

• D. Fossils are dated based on the types of minerals found in the surrounding soil, without any reference to volcanic ash.

What information is needed to determine the age of a rock sample using radioactive decay?

Remember our Lab on Half-Life

• The relative amounts of uranium-238 and lead-206.

• The temperature of the rock sample.

• The color of the rock sample.

• The size of the rock sample.