The document describes the three main layers of Earth - the crust, mantle, and core. The crust is the outermost layer and is made up of different elements. Below the crust is the mantle, which makes up most of Earth's volume and is divided into the lithosphere and asthenosphere. The innermost layer is the core, which is divided into the liquid outer core and solid inner core. Seismic waves have revealed details about these layers and seismic discontinuities exist where properties change between layers.

1. LAYERS OF EARTH

2. • Scientists infer most of the properties of
Earth’s interior through the study of
SEISMIC WAVES.
• They have discovered that seismic
waves refract, reflect, change velocity,
and become absorbed by various parts
of the Earth’s interior.

3. THREE DISTINCT LAYERS OF EARTH
1.CRUST
2.Mantle
3.Core

4. 1. CRUST
• The crust is the outer layer of Earth.
• It is approximately 15 to 50 km deep and includes the continents
and the ocean floor. Different elements such as:
• Oxygen (46.6%)
• Silicon (27.7%)
• Aluminum (8.17%)
• Iron (5.0%)
• Calcium (3.6%)
• Potassium (2.8%)
• Sodium (2.6%)
• Magnesium (2.1%) ,make up Earth’s crust.

5. 1. CRUST
• Evidences indicate that Earth’s crust
constantly undergoes change.
• Occurrences of earthquakes, volcanic
eruptions, the rising of mountains, and
the shifting of landmasses’ positions are
proofs of the crust’s movements.

6. 2. MANTLE
• The mantle is the Earth’s thickest layer, making up about 87% of its total
volume.
• It is located between the core and the crust. The composition of mantle is 46%
silicon oxide, 38% magnesium oxide, 8% iron oxide, and 8% other
compounds.
• The upper mantle has two parts that are often seen as distinct regions in
earth’s interior: the lithosphere and the asthenosphere.
a. The LITHOSPHERE is made up of the crust and the upper mantle. It is the
coolest and most rigid of Earth’s layers. Tectonic activity occurs in the
lithosphere.
b. The ASTHENOSPHERE is the denser layer beneath the lithospheric
mantle. It extends from 100 km to 700 km below Earth’s surface.
Convection currents produced in the asthenosphere push the magma
upward through volcanic vents, resulting in the creation of new crust and
the manifestation of earthquake.

7. 3. CORE
• The core is the innermost region of Earth.
• The core is divided into the molten outer core and
solid inner core.
• The outer core is 2253.9 km thick and is made up of
iron and nickel with small amount of dense
elements like gold, platinum, and uranium.
• The inner core is approximately 1207 km thick and
is made up of iron.

8. SEISMIC DISCONTINUITIES
• Seismic discontinuities are the places in the
Earth where there is abnormal behaviour by
the seismic waves due to the change in
physical and chemical properties.
• DISCONTINUITY is a term in geology that
refers to a surface in which the seismic
waves change velocity.

9. • Some of the discovered seismic discontinuities are the
Mohorovicic Discontinuity and the Gutenberg Discontinuity.
a. MOHORVICIC DISCONTINUITY, or “Moho,” was
discovered by a Croatian seismologist named Andrija Mohorovicic
in 1909.
According to Mohorovicic, the veolocity of a seismic wave is
relative to the density of the material through which it travels.
He explain that seismic waves travel faster in the denser regions
of earth’s inner structure.
He interpreted that within Earth’s outer shell, the velocity of
velocity of seismic waves changes as the composition within
earth changes.
The Moho separates the crust from the mantle, with an average
depth of about 8 km beneath continental surfaces.

10. b. GUTENBERG DISCONTINUITY
The Gutenberg discontinuity, also
referred to as Oldham-Gutenberg discontinuity
or the Weichert-Gutenberg discontinuity, is
found below 2900 km from Earth’s surface and
lies between the lower mantle and the outer
core