What was the first rock in the rock cycle?

Question

I am an undergraduate student but I am a tutor at a High School, and one student asked me. Attempting to explain the rock cycle "if one rock turns into the other then which came first" my gut is telling me probably igneous (given Earth geologic past.) Resources online have different opinions. Am I right in my assumption?

Answer 1

The rock cycle is a cycle for a reason-- any rock can turn into any other rock. But I suppose if the question is 'what was the first rock type ever' then I would say igneous as it would has crystallized from the magma ocean in the Archean. But very quickly after that we would have started to make metamorphic rocks. As continents formed, weathering started to take place then producing sedimentary rocks.

But this is just my opinion!

Answer 2

I concur with your answer. There are 3 categories of rock; igneous, sedimentary, and metamorphic. The last two are products of any combination of the three types and physical forces (pressure, heat, weathering, gravitational transport, chemical reaction).

Igneous rocks are "born" within the internal layers of the deep crust and mantle. Therefore, they are the "first" rocks and form the original lineage from which all other rocks are descendent.