The earth is more than 4.5 billion years old, but some asteroids are older still.
The core of the earth is mostly made of iron and nickel. This rotating metal core produces earth's magnetic field.
The mantle and outer core are kept hot by the decay of radioactive elements.
Basalt and limestone are some of the most common minerals on earth. Basalt is made from lava flows, whereas limestone is the compacted remains of ancient shells.
Most minerals are made in the upper mantle and are slowly brought upwards by tectonic action.
The continental crust is much older than the seafloor. The seafloor is recycled via subduction on a regualr basis (geologically speaking), while the continental crust hangs around.
There have been several supercontinents throughout history; the first was Rodinia, and the last was Pangea. Geologists millions of years from now may consider the Afro-Eurasian landmass to be another. I am particularly fond of Gondwanaland myself.
The moon used to be much closer to the earth but has been slowly drifting away for eons. Tides were much more intense on the young earth.
Most of the heavier elements have migrated to the mantle and core, meaning the crust is largely made of oxygen, silicon, and aluminum.
In rare places, the mantle rock has been exposed. They call this material serpentite.
Every element on earth exists at some concentration dissolved in the seawater. Currently, magnesium and uranium are the only ones which might eventually be worth extracting.
When silicon combines with water under the right circumstances, it becomes silicon dioxide. This hard, clear material is one of the most common minerals, and is called quartz.
The core of the earth is approximately 11,000 degrees. While it is not inconceivable that materials could be made to withstand this, the pressures in the core will defeat our machinery for many years.
The inner core is under so much pressure that the metals are solid despite the temperature. They do not have enough room to expand and melt.
The magnetic poles of the earth have been known to switch, due to a poorly understood mechanism. The magnetic north pole has sped up its migration, moving about 40km per year. The reason for this is unknown.