Question

What are the three compositional layers in Earth's interior? a) Asthenosphere, lithosphere, core b) Oceanic crust, continental crust, asthenosphere c) Lithosphere, mantle, core d) Crust, mantle, core

Short answer

d) Crust, mantle, core

Step-by-step solution

Understand the compositional layers

The compositional layers of Earth's interior refer to the different layers that make up Earth based on their chemical composition. These are traditionally known as the crust, mantle, and core.

Examine each option

- **Option a**: Includes 'asthenosphere', which is a mechanical layer, not a compositional layer. - **Option b**: Mentions 'oceanic crust' and 'continental crust', which are parts of the crust, not separate compositional layers. 'Asthenosphere' is also a mechanical layer. - **Option c**: Lists 'lithosphere', a mechanical layer comprising part of the crust and upper mantle, not a compositional layer. - **Option d**: Lists 'crust, mantle, core', which are the correct compositional layers.

Determine the correct answer

After analyzing each option, we identify that option d) Crust, mantle, core represents the traditional classification of Earth's compositional layers.

Key concepts

Crust

The Earth's crust is the outermost layer of our planet. It's the part we live on and is known for being thin compared to the other layers. The crust consists of two main types: **continental crust** and **oceanic crust**.
- **Continental crust** is thicker and less dense. It contains a variety of rocks, with granite being quite common.
- **Oceanic crust** is thinner and more dense. It is mostly composed of basalt, a dark volcanic rock.
The crust varies in thickness from about 5 km under the oceans to about 70 km under the continents. It's like a thin skin that floats on the more fluid mantle below. This floating is possible due to the crust's lower density, forming a balance similar to how an iceberg floats on water.
Understanding the crust is important because it's where we find all the resources essential for life, such as minerals, water, and the soils in which plants grow.

Mantle

Beneath the crust lies the mantle, a thick layer of rock that extends to a depth of about 2,900 km. The mantle makes up about 84% of Earth's volume, which is immense!
- The **upper mantle** is cooler and more rigid compared to the lower parts. It's involved in plate tectonics and earthquakes, as it forms the lithosphere along with the crust.
- Below this is the **asthenosphere**, a semi-fluid layer that allows tectonic plates to move. This movement is responsible for most of the geological activity we observe on Earth, like earthquakes and volcanic eruptions.
The mantle is predominantly composed of silicate minerals, rich in iron and magnesium. The temperature and pressure increase with depth, leading to gradual changes in its physical properties. Convection currents, driven by heat from the deeper core, cause the hot material to rise and cooler material to sink, resulting in a slow, flowing movement inside the mantle. This continuous process is crucial for the dynamic nature of our planet.

Core

At the heart of the Earth lies the core, which is separated into two distinct parts: the **outer core** and the **inner core**.
- The **outer core** is liquid and composed mainly of iron and nickel. It is responsible for generating Earth's magnetic field through the movement of its molten metal. This magnetic field is vital as it protects the planet from harmful solar radiation.
- The **inner core** is solid despite the extremely high temperatures, which exceed 5,000°C. The immense pressure at Earth's center keeps it in a solid state.
The core is incredibly dense and forms about 15% of Earth's volume. Studying the core helps scientists understand phenomena such as the planet's magnetic field and how it has changed over geological time. This knowledge is gathered through indirect methods, like the analysis of seismic waves from earthquakes, which help scientists infer the core's properties and behavior.