Question

The oldest rocks found on Earth are 3.96 billion years old. However, scientists believe the Earth is about 4.6 billion years old. What evidence supports this idea? Choose all that apply.

Answer 1

As the earth has active tectonics we know that rocks are recycled and the oldest rocks may therefore just be the oldest rocks that have not been recycled yet. We know the true age of the earth by looking at radioactive isotopes of things like spacedust and meteors that formed at the same time as the earth as they have not been affected by the tectonic process of recycling here on Earth.

Answer 2

The Earth is 4,54 billion years old. This age has been determined with the radioactive dating technique. The precise decay rate of radioactive elements is used as a clock: the number of daughter products in one rock indicates its age.

The oldest meteorites ever dated in the Solar System are 4,56 billion years old, the oldest minerals on Earth are 4,4 billion years old, and the oldest rocks on Earth are 4 billion years old. These ages are very consistent because the meteorites had to form before the accretion of our planet, and the Earth had to cool down before the first minerals could crystallise.

The Solar System was formed around 4.6 billion years ago, out of the collapse of a dense cloud composed of dusts and gases. Meteorites, which are the very components of our planets (through the process of accretion), are the remnants of the Solar System’s origins. Dating meteorites thus allows us to give a lower age to the Solar System (4,56 billion years old).