Mohorovičić discontinuity

The Earth has layers.

One layer is the hard crust. Below that is the mantle. A special line sits between them.

This line is called the Moho. A man named Andrija Mohorovičić found it. He studied waves from earthquakes. These waves move through the ground.

The waves change speed at the Moho. This happens because the rocks change. The rocks get much denser there.

The line is deep under the ocean. It is even deeper under land. It helps us see inside our world.

The Earth has different layers. One layer is the crust. The layer below it is the mantle.

A special boundary sits between these two layers. It is called the Mohorovičić discontinuity. Most people just call it the Moho.

A scientist named Andrija Mohorovičić found it in 1909. He studied waves from earthquakes. These waves are called seismic waves. They move through the ground.

He saw that these waves change speed. This happens because the rock changes. The rock gets much denser at the Moho. This change in density makes the waves move faster.

The Moho is deep under the ocean. It stays at an average depth of 10 km there. Under the land, it can be much deeper. It can go down more than 70 km.

Scientists still want to reach the Moho. They try to reach it by drilling deep holes. Some projects use special ships to drill in the ocean. They want to learn more about our world.

The Earth has many different layers. One layer is the crust. The layer below it is the mantle.

Between these two layers sits a special boundary. Scientists call it the Mohorovičić discontinuity. Most people just call it the Moho. This boundary is very important for Earth science. It marks where the crust ends and the mantle begins. Understanding the Moho helps us learn about our planet.

We can find the Moho by watching seismic waves. These are waves caused by earthquakes. When these waves travel through the ground, they change speed. They move through different types of rock. Above the Moho, waves move through basalt. This rock is part of the crust. Below the Moho, the waves move through peridotite or dunite. These rocks are part of the mantle.

The waves speed up by about 1 km/s when they hit this layer. This happens because the rock becomes much denser. The Moho is a transition zone up to 500 meters thick.

A scientist named Andrija Mohorovičić discovered this boundary. He was a seismologist from Croatia. In 1909, he studied an earthquake in Zagreb. He saw two different sets of waves on his records. These were called P-waves and S-waves. One set of waves traveled a direct path near the surface. The other set was refracted by a high-velocity medium. Refraction means the waves bent as they moved.

He realized this happened because of a sharp change in density. He calculated the Moho was about 54 km deep.

The Moho is not at the same depth everywhere. Under the ocean floor, it stays near 10 km deep. Under large land masses, it can be much deeper. It can go down more than 70 km. In the 1960s, a group tried to reach it. This was called Project Mohole. They wanted to drill into the Moho from the ocean. The project was cancelled in 1966 due to costs. Other scientists tried to drill in Russia. The Kola Superdeep Borehole reached 12,262 meters by 1992.

Scientists still work hard to reach the Moho today. They use big ships to drill deep into the sea. One ship is called the Chikyū. It is part of the Earth Discovery project. In 2015, a ship called the JOIDES Resolution sailed from Sri Lanka. It went to the Atlantis Bank in the Indian Ocean. The team tried to drill a hole 1.5 kilometers deep. They did not reach that goal, but they keep trying. Reaching the Moho helps us see the Earth's interior.

The Mohorovičić discontinuity is a major boundary within Earth. Most scientists simply call it the Moho. It marks the specific place where the crust ends and the mantle begins. This boundary is vital for understanding the structure of our planet. It helps geologists distinguish between the outer rocky shell and the dense layer beneath it.

Scientists identify the Moho by measuring seismic waves. These waves are vibrations caused by earthquakes. When these waves travel through the Earth, they change speed based on rock density. Above the Moho, primary waves, or P-waves, travel through basaltic rock. These waves move at speeds between 6.7 and 7.2 km/s. Once the waves pass the Moho, they enter the mantle. Here, they travel through rocks like peridotite or dunite at speeds of 7.6 to 8.6 km/s. This jump in speed is about 1 km/s. This change happens because the mantle is much denser than the crust.

The Moho is not a thin, perfect line. Instead, it is a transition zone that can be up to 500 meters thick. The depth of this boundary varies greatly depending on where you are. Under the ocean floor, the Moho is relatively shallow. It maintains a stable average depth of about 10 km. However, beneath large continental land masses, it can be much deeper. It can vary by more than 70 km in these areas.

Geologists have found that the Moho is quite complex. It does not always match the boundary where rock composition changes. In some areas, basaltic intrusions can make the transition up to 20 km thick. This occurs away from stable continental cratons. Additionally, a process called serpentinization can affect the boundary. This happens at slowly spreading mid-ocean ridges. Serpentinization involves mantle rock changing in a way that lowers seismic wave velocities. This can increase the measured depth to the Moho.

A Croatian seismologist named Andrija Mohorovičić discovered this boundary in 1909. He was studying data from an earthquake near Zagreb. He noticed two distinct sets of P-waves and S-waves. One set traveled a direct path near the surface. The other set was refracted, or bent, by a high-velocity medium. Mohorovičić realized that waves travel at speeds proportional to the density of the material. He theorized that the second set of waves hit a sharp change in density. Using this data, he calculated the Moho was approximately 54 km deep. His work helped create the field of modern seismology.

Humans have long tried to reach the Moho through drilling. In the 1960s, a mission called Project Mohole attempted to drill from the ocean. The project was eventually cancelled in 1966 due to costs and mismanagement. Other scientists tried a different approach in the Soviet Union. They worked on the Kola Superdeep Borehole from 1970 until 1992. This project reached 12,262 meters, which is the deepest hole in the world. Even so, it did not reach the Moho.

Today, scientific exploration of the Moho continues with advanced technology. The Japanese project Chikyu Hakken uses the drilling ship Chikyū to explore these deep areas. Other researchers use the drill-ship JOIDES Resolution. In late 2015, this ship traveled to the Atlantis Bank in the Indian Ocean. The team aimed to drill a hole 1.5 kilometers deep. Although they did not reach that specific depth, the mission provided important data. Some scientists even propose using a special capsule to reach the boundary. This capsule would use a tungsten needle to propel itself into the upper mantle.