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00:00Hi kids! Today we will learn about rocks. So let's start.
00:07Rocks are naturally existing solid matter that exist in nature and are
00:14made up of combinations of one or more minerals. We will learn what minerals are
00:21later on. Where can you find rocks on earth? You will find rocks on most of the
00:30places on earth. Here are a few examples. Beaches have big stones. Garden soil has
00:39stones in it. Seabed has a lot of stones. Surrounding area of a volcano has stones.
00:48Caves are made up of stones. You can find big stones on mountains. Deserts also
00:57have a lot of stones. So there are just so many places where you can find rocks.
01:05Scientists who study the earth are called geologists. Geologists study about
01:12rocks and minerals as rocks and minerals are the best examples to
01:18understand the evolution of our earth. Rocks tell geologists about what
01:25happened on earth millions of years ago. Rocks and minerals also tell about what
01:32is there at the center of the earth. Rocks also tell us about the possible
01:39locations of volcanoes and which places can be centers of earthquakes. Rocks can
01:47be categorized into three categories. Igneous, sedimentary, and metamorphic. Now
01:57let's learn about each one by one. Igneous rocks. Igneous rocks are of two
02:07types. Intrusive igneous rocks and extrusive igneous rocks. Let's first
02:14learn what are intrusive igneous rocks. There is magma that is hot molten matter
02:21present deep inside the earth's surface.
02:27Sometimes this molten matter cools down, hardens, and forms rocks. These rocks
02:35formed inside the earth's surface are called intrusive igneous rocks. Igneous
02:43rocks are made up of large crystals because the cooling of molten matter
02:48occurs at a slow rate below the earth's surface. This is why large crystals are
02:56formed in intrusive igneous rocks. Examples of intrusive igneous rocks are
03:03diorite, gabbro, granite, pegmatite, and peridotite.
03:13Lava. When this molten matter or magma comes out of the earth's surface by
03:20rupturing it, it's known as lava. This lava too cools down and forms rocks. And
03:29rocks formed by cooling down of lava outside the earth's surface are called
03:35extrusive igneous rocks. Extrusive igneous rocks have smaller crystals and
03:44are shinier. It is because the lava outside the earth's surface cools down
03:51quickly and forms smaller crystals that shine. So kids, we learned that igneous
03:59rocks are of two types, intrusive igneous rocks and extrusive igneous rocks. When
04:09the hot molten matter inside the earth's cools down, it forms intrusive igneous
04:15rocks with bigger crystals as the molten cools at a slower rate. And then the lava
04:24comes out of the earth's surface and cools down outside the earth. It forms rocks
04:30with shinier and smaller crystals and they are known as
04:36extrusive igneous rocks. The crystals in extrusive igneous rocks are smaller in
04:44size because of the molten matter outside the earth's surface cools down very
04:50quickly. Now let's learn about another type of rock known as sedimentary rocks.
05:00Sedimentary rocks are made from sediments like particles of sand, shells,
05:07pebbles, other rocks. Let's learn how they are formed. There is continuous
05:17breakdown of different types of rocks into smaller pieces due to the action of
05:23forces like wind, rain, sea waves, plants, animals, changes in temperature and
05:32pressure. This breaking down of rocks into smaller pieces of rocks is called
05:39weathering. These are some beautiful shapes of rocks formed by the continuous
05:47weathering over the years. And where do these small weathered pieces of rocks go?
05:56Erosion. These small pieces of broken rock particles and minerals are carried
06:03away by water, air and this carrying away of small pieces of rocks is called
06:09erosion. And due to erosion the small pieces of rocks reaches the water bodies
06:17and settled down in the beds of water bodies. This is called sedimentation. And
06:25many layers of sediments accumulate over the passage of years and under the
06:31pressure of seawater. A process called compaction occurs and the layers of
06:37sediments are hardened and they form sedimentary rocks. Organic matter that is
06:46dead and decayed plants and animals get trapped into these layers and form
06:52fossils. Sedimentary rocks are made up of layers called strata. The layer at the
07:01bottom is the oldest one and the topmost layer is the newest one. There are six
07:09main types of sedimentary rocks including conglomerate, sandstone, shale,
07:16limestone, gypsum and grisha. Now let's learn another type of rocks called the
07:25metamorphic rocks. Sometimes the sedimentary rocks and igneous rocks are
07:32trapped at a great depth beneath the earth's surface and there is very high
07:37temperature and pressure. And this extreme pressure and temperature make
07:44the rocks undergo physical and chemical changes called metamorphosis. And
07:51sedimentary or igneous rocks change to metamorphic rocks. These rocks have
07:58layers and may also shine like crystals.
08:04Examples of metamorphic rocks include genesis and marble. So kids, today we
08:14learned about different types of rocks. In our next assignment we will learn
08:19about minerals. Now you may go ahead and take a quiz to learn more. Bye bye!