Lesson 25: Special text: The Earth’s crust, rocks, minerals Read and translate the text

LESSON 25:

Special text: The Earth’s crust, rocks, minerals

Read and translate the text.

What lies deep within the Earth? Our planet has a central core with several layers, or shells, surrounding it. The densest matter is at the center, and each layer above it is increasingly less dense.

THE EARTH’S INTERIOR

Our planet is almost spherical, with a radius of approximately 6400 km (about 4000 mi). Its central core is about 3500 km (about 2200 mi) in radius (Figure 11.1). We know that the outer core is liquid from measurements of earthquake waves passing through the Earth, which suddenly change behavior when they reach the core. But the innermost part of the core is solid and made mostly of iron, with some nickel. The core is very hot—somewhere between 3000°C and 5000°C (about 5400°F to 9000°F).

MINERALS AND ROCKS

Minerals are naturally occurring inorganic substances, often with a crystalline structure. They are composed largely of the most abundant elements in the Earth’s crust, silicon and oxygen, coupled with metals or the metallic elements of iron, calcium, sodium, potassium, and magnesium.

Rocks are usually composed of two or more minerals. Often, many different minerals are present, but a few rock varieties are made almost entirely of one mineral. Most rock in the Earth’s crust is extremely old, dating back many millions of years, but rock is also being formed at this very hour as active volcanoes emit lava that solidifies on contact with the atmosphere or ocean.

Rocks fall into three major classes: (1) igneous, (2) sedimentary, and (3) metamorphic rocks. The three classes of rocks are constantly being transformed from one to another in a continuous process through which the crustal minerals have been recycled during many millions of years of geologic time. 

Activity 1. Find the definitions and synonyms of the words which are given in bold in the text.

Activity 2. Complete the table.

Word	Definition	Synonym