Elements, they are the basic building blocks of all matter and found everywhere. They are what form the Earth, and everything upon it. Even if you believe in God, he still made the elements to make us! They are what comprise the rocks that form the mountains, the water in which fish swim and the air which living things breath. Some elements are more abundant than others, but what are the most abundant elements on Earth? It may depend on how you define on Earth, does it include the atmosphere and oceans, or just the earth's crust?
Lets start at the center, the core of the planet is reportedly heavy metals, but mostly iron. That also seems to come to the surface in several places and was the reason there was an iron age. It would be interesting to see what the planet would be like without iron, it is even the basis for most blood! Iron is definitely one of the most abundant elements on Earth.
Another element that is common and down to earth is Silica. Silica, and Silica compounds are found in the sea, on the beaches and virtually everywhere. It is Silica from which is what glass is made.
And over 70% of the planet is covered in water, which is composed of two element, hydrogen and oxygen. The water is not only in the oceans, but on the land, under the land and even in the air. Oxygen and hydrogen are also common in the air, and in every living thing on the planet. There are few if any elements more abundant that Hydrogen and Oxygen.
An abundant element contender, if we include atmosphere would be nitrogen, it comprises almost 78% of the air we breath. Some people try to include carbon dioxide, but that is a compound comprised of two elements, carbon and oxygen, we have already listed the oxygen, but can include carbon.
Carbon is not only in the air, but in the seas, that is how reefs form, coral polyps bind the carbon to form calcium carbonate, coral. Carbon is also the main basis for life on Earth. It is found in every living thing and is also what coal is made from, diamonds and even graphite.
Need a few more abundant elements on Earth? Try Calcium, sodium, aluminum, and even chlorine. There are all as common as dirt and abundant!