Astrum
How do we know the universe is 13.8 billion years old?
How can scientists possibly know the age of the universe? Well, through a variety of factors, including redshift, the CMBR and more.
Khan Academy
Cosmological Time Scale 1, Scale of the Universe, Cosmology and Astronomy
A scaled timeline highlights periods relevant to us since the Big Bang. Events on the timeline include the formation of Earth, the extinction of dinosaurs, and the emergence of modern humans.