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By: Efraim Harari

Planet Earth has multiple layers and consists of many parts. We live on the outermost layer of the planet, called the crust. The thickness of the crust varies between three and forty-six miles deep. The thickest parts of the crust are under the continents, and the thinnest parts lie under the oceans. The crust is composed of mostly oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. About 71% of Earth’s surface is covered by the oceans.

The layer underneath the crust is called the mantle, which is about 1800 miles deep. The mantle is made up of rock containing silicon, iron, magnesium, aluminum, oxygen, and other minerals.

Below the mantle, at the center of the Earth, lies the core. The core has two parts: the inner core and the outer core. Both cores are mostly made up of iron and nickel. The outer core is in a liquid state and is about 1,400 miles thick. The inner core, however, is solid, and has a radius of about 750 miles.

Crust:The crust is divided into huge blocks called tectonic plates, which float on the mantle, the layer below the crust. These plates are constantly moving (very slowly), which is what causes the formations of mountains, valleys, earthquakes, and other geologic activities.

Mantle:The mantle is the thick layer of rock below the crust. Heat from Earth’s core keeps the mantle moving slowly, which causes the tectonic plates to move around.

Outer Core: Earth's outer core has a temperature greater than 7,200 degrees Fahrenheit! The intensity of the heat is what turns the iron and nickel metals which the outer core is made up of into a liquid state.

Inner Core: The inner core is the hottest part of the Earth, with a temperature greater than 9,800 degrees Fahrenheit! The inner core is so deep within the earth that it's under immense pressure – so much so that, even though it is so hot, the inner core still remains solid
(unlike the outer core).

Slow Motion

Tectonic plates move between one and eight inches per year — the same rate at which fingernails grow.

Did you know that people once
thought Planet Earth was flat?

Although today this notion seems quite silly, it was not too long ago when many people believed that Earth was flat. After all, in any place with a wide view, the horizon looks flat. If we did not know how gravity works, then it might be hard to imagine a round Earth, since, without gravity, why wouldn't we fall off a round world? That is why so many cultures, including Ancient Egyptian, Babylonian, and Chinese cultures, believed that the world was a flat disk rather than a sphere. And for this reason, many people were afraid to set sail, assuming that they would fall off the world if they reached the edge of it.

It was only in a much later time period (between 500 to 700 BCE) that some Greek philosophers began to realize that the world is round. But even then, the majority of mankind still believed that Earth was flat, or at best, dome-shaped.

After Christopher Columbus discovered America in 1492, while traveling west in search of a shortcut to India, many people became inspired. They realized that if sailors were traveling and returning safely, it must be safe to sail after all, and they, too, set out on similar voyages of discovery. Slowly but surely, people began to realize that you can’t “fall off the edge of the Earth” – because the Earth is indeed round and not flat.

Water Works

About 97% of Earth’s water lies in the oceans. The remaining water can be found in ice (about 2%) and in fresh water or water vapor in the atmosphere.

Torah Tidbit

Chazal knew that the world was not flat, from the wisdom of the Torah. The Zohar, which was written over 2,000 years ago, quotes a sefer written even earlier by Rav Hamnuna Saba:

The entire world and those upon it spin around in a circle like a big ball, both those at the bottom of the ball and those at the top. All of Gd's creatures, wherever they live on the different parts of the ball, look different (in color, in their features), because the air is different in each place, but they stand erect like all other human beings. Therefore, there are places in the world where when some have light, others have darkness, [and] when some have day, others have night. (Zohar 3:10a)

From here we can see that already long ago, Chazal knew that the world is shaped like a ball, and is not flat, as was the belief of the science of the times.Chazal also knew that the Earth is not fixed permanently in one place, but spins and turns on its own axis, and that people live on both sides of the planet.

In Good Shape

Earth is not a perfect sphere. It is a unique shape called a geoid — which means “Earth shaped.”