All the information we get about the interior of the earth is indirect and based on conjecture.
Analysis of the properties of matter found underground provides indirect information about the Earth's internal structure.
The main indirect sources are as follows.
$(1)$ Density: The average density of the earth is $5.5 g / cm^3.$
The density of rocks on the surface of the earth is $2.7 g / cm^3.$
While the density of igneous rocks beneath the mulch is $3.0$ to $3.5 g /$ cubic cm.
The density of the interior of the earth is about $11$ to $12 g / cm^3.$
The density of the Earth was first measured in $1774$ based on Newton's law of gravitation.
$(2)$ Pressure: The upper layers of the earth exert pressure on the lower layers.
As we move towards the center of the earth, its density increases due to increasing pressure.
$(3)$ Temperature: usually increases by $1^\circ C$ at a depth of $32\ m$ each.
At this rate the temperature of the central part of the earth is $10000^\circ C.$ Is estimated to be even higher than.
This is evidenced by the hot gases emitted during volcanic eruptions, the liquid lava hot springs, and the fountain water vapor.
$(4)$ Meteors: Heavy metals like iron and nickel are obtained from meteors.
It therefore proves that the central part of the earth will contain heavy metals which are also members of the solar family like the meteors.
$(5)$ Gravity: The force of gravity is felt differently on different parts of the earth's surface.
Since the center of the earth is relatively close to the poles, the force of gravity on the poles is greater than the equator.
Since the center of the earth is far from the equator, the force of gravity here seems to be less than that of the poles.
$(6)$ Magnetic surveys: Magnetic surveys have proved that the distribution of geological substances in the interior of the earth is uneven.
$(7)$ Seismic waves: Three types of seismic waves are noted by the seismographer.
$(1)$ Primary waves $(2)$ Secondary waves $(3)$ Surface waves. Based on the measurement of these waves, scientists have divided the Earth into three parts from the interior to the center.