Hydrogen only makes up 0.14% of the earth's crust, so it is not nearly as common as oxygen (46%) or silicon (28%). Hydrogen is the 10th most abundant-by-mass element in the Earth's
Hydrogen is of course a key component of a substance we living creatures consider to be very important -- H2O, water. Besides water, humans (and all other life)
are composed largely of hydrocarbons. Hydrogen is, therefore, the most common element in living things on Earth.
Therefore, the first thing that would be very
different if the Earth's crust had no hydrogen (no
water), would be that life (if it existed) would be chemically completely different than what we currently have.
As far as geology is concerned, water (and therefore hydrogen), is also very important. Even a tiny amount of water greatly changes the chemical reactions in the crust. It makes it much easier for hot rocks to melt into magma.
Therefore, without water, plate tectonics and volcanoes would behave differently. Maybe volcanoes would be less common and less explosive. Also, erosion of rocks and deposition of sediments usually occurs by water.
So, without hydrogen, the surface of the
earth would not have water to shape it and would
look very different. Think of the world with no
rivers, lakes, oceans, or life.
I never realized how much I like hydrogen.