Time scale of the universe

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The time scale of the universe refers to the relative size of the universe and all events occurring within it. Best estimates show that the universe has been around for 13.8 billion years. It started with the Big Bang, and expanded rapidly. All of the energy and mass[1] in the universe seems to come from that one gigantic explosion that is clearly the biggest explosion that is known about. Everything that exists was formed either directly or indirectly from the Big Bang.

Roughly 5 billion years ago, 8 billion years after the Big Bang, a star exploded[2] and formed the solar system, including the Earth, over the course of hundreds of millions of years. This means that Earth was formed 4.6 billion years ago, quite a bit after the Big Bang. Life formed fairly soon after the Earth formed. The 'life' link in visualization below[3] shows this. By contrast, genus Homo has only been around for 250,000 years, and of that time evidence exists for only 5000 years of recorded history.[4]

Large time scales of millions or billions of years can be difficult to properly imagine. The Chronozoom website is a project dedicated to showing scale comparisons in the enormous time scale of the universe. Their interactive visualization shows the known past timeline of the entire cosmos. Click on the 'Earth' link along the top, or inside the 'Earth and Solar System' box in the image to zoom into the last 4.5 billion years. Click on the 'prehistory' link along the top to get an idea of human prehistory. Click on the 'humanity' link along the top to get an idea of the last 5000 years of human history. Click on the box in the upper right hand corner to see the industrial revolution, when coal started getting used extensively to change the way humans live.


  1. also, oddly, time and space, see here for a lecture by Prof. Steven Hawking on the subject, although we go with the 13.8 billion year rather than 15 billion year time that he gives: http://www.hawking.org.uk/the-beginning-of-time.html.
  2. See nova and supernova on hyperphysics for more information.
  3. Chronozoom.com Copyright (C) 2013. The Outercurve Foundation. All rights reserved.
  4. Which we've defined as history confined to written records