What significant event occurred about 380,000 years after the Big Bang started?
A) The universe became transparent to radiation.
B) All of the present galaxies in the universe were formed within a short time span.
C) The temperature of the radiation decreased to 2.76 K.
D) The solar system was formed.

Question

Quizplus · Accepted Answer

About 380,000 years after the Big Bang, the universe cooled down enough for the electrons to combine with the nuclei and form neutral atoms. This made the universe transparent to radiation, allowing it to travel freely and be observed as the cosmic microwave background radiation.

What Significant Event Occurred About 380,000 Years After the Big