Though the Earth seems to be just a rock flying through space; this rock is very much active and it is this activity that makes this planet habitable, unlike other plants such as Mars (read more here). The planet is constantly changing as it follows phenomena that far exceeds the existence of humans and will continue to change once we’re long gone. Let’s have a look at the structure of the Earth as well as the rock cycle.
The Earth is approximately 1.08321 x 10¹² km³ and is broken up into layers – think of an egg – which can be broken up either due to physical or chemical properties. The basic physical structure of the Earth can be broken up into the crust, the mantle, the outer core and the inner core. The crust varies in thickness from 5 to 70 km with an average of 50 km thick. This is the shell of the Earth that we all live on and it has never been completely penetrated; we’ve made it approximately a third through the average crusts depth. Next is the mantle where variations in physical and chemical properties start to separate the layers differently. The mantle (50 – 2890 km deep) in general is a relatively low-viscosity layer in which molten rock circulates due to convection currents forming from the incredibly hot core.
Combined parts of the crust and uppermost mantle can chemically be labelled as the lithosphere (0 – 60 km deep) and the layer just below is the asthenosphere (100 – 700 km deep). The lithosphere is the section of the Earth that is broken into the 7 major and approximately 10 minor tectonic plates which move thanks to the convection currents occurring within the asthenosphere. Next, the outer core (2890 – 5100 km deep) is a liquid alloy if iron and nickel, and is liquid because of the immense heat that comes from the inner core (5100 – 6378 km deep); heat generated from the creation of this planet. The inner core is a solid alloy of the two previously mentioned elements and is solid due to the pressure applied by the earth around it. The slight angular spin of the inner core in the outer core is believed to form a complex array of electromagnetic currents that form the dynamo and protect the planet from cosmic radiation from deep space and radiation from the sun. Let’s now look at the rocks.
The rock cycle is the recycling of finite resources on the Earths upper layers that result in the change of surface structures and relocation of entire continents; let’s start with molten rock. When magma cools, either intrinsically (inside) or extrinsically (outside), igneous rocks are formed (ignis = Latin for fire). When intrinsic, the magma cools slowly so the crystals within the rocks are quite large in comparison to the slow cooling that takes place during extrinsic cooling; takes places outside of the crust (volcanic eruption). Igneous rocks can then become 1 of 2 other types of rocks; sedimentary or metamorphic.
Sedimentary rocks are rocks that are formed because of sediments. Thanks to weathering and erosion (read more here), igneous and metamorphic rocks can be broken down into sediments which then wash downhill into larger bodies of water. Here, the sediments settle to the bottom (depending on the activity of the water source) and starts to form layers. These layers are then cemented together over time as more and more layers are added on top, supplying pressure. It is within sedimentary rocks that fossilized remains can be uncovered as previously alive organisms are buried under sediment and the tissues are replaced with different minerals.
Igneous rocks that are formed intrinsically or sedimentary rocks that are then buried further underground over time can be exposed again to the heat and pressures of the surrounding earth (push your hands together hard and you’ll feel the heat from pressure). The pressure is supplied thanks to plate tectonics which is the movement of the lithosphere on the asthenosphere. This movement causes continents to move as well as causes landmasses to crash into one other forming mountain ranges. This compresses and warps the rock, forming metamorphic rock. Further exposure to heat on either metamorphic or sedimentary rock cause it to melting forming magma and the cycle begins a new. The Earth is approximately 4.5 billions years old and it is this cycle of recycling and change that has created the beautiful land that we are blessed to live upon; it’s something to be grateful for.