09 The History of Earth Free Online FlashCards

How old is Earth?

Earth is about 4.54 billion years old.

How is geologic time organized?

Geologists divide Earth’s history into eons, eras, periods, and smaller intervals.

What does the order of undisturbed sedimentary layers reveal?

In undisturbed sedimentary rocks, lower layers are generally older than the layers above them.

How does radiometric dating estimate a rock’s age?

Radiometric dating estimates numerical ages by measuring radioactive isotope decay in minerals.

How did Earth’s early materials separate into layers?

Dense iron-rich material sank toward the center to form the core, while lighter materials rose to form the mantle and early crust.

What is the leading explanation for the Moon’s formation?

A giant impact with a planetary body is the leading explanation for the Moon’s formation.

How did volcanic activity and cooling help form the atmosphere and oceans?

Volcanoes released gases that helped form an early atmosphere. As Earth cooled, water vapor condensed and liquid water accumulated in oceans.

How do sedimentary rocks form, and what can they preserve?

Sedimentary rocks form when particles or dissolved minerals are deposited and then compacted or cemented. They can preserve fossils and environmental clues.

How do metamorphic rocks form?

Metamorphic rocks form when existing rocks are changed by heat, pressure, or fluids without fully melting.

How can granite become metamorphic rock through the rock cycle?

In one example, granite weathers into grains, erosion carries them, and they may form sandstone. Burial and heat can then transform the sandstone into metamorphic rock.

How do plates move at spreading, convergent, and transform boundaries?

At spreading boundaries, plates move apart and new ocean crust forms. At convergent boundaries, they collide; at transform boundaries, they slide past each other.

What causes an earthquake?

An earthquake occurs when stress along a fault builds until rocks suddenly slip.