What is the Age of the Solar System?

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  • 0:01 What Is Your Real Age?
  • 1:07 The Solar System & the…
  • 1:53 Half-Life & the Age of…
  • 5:12 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will tell you how old our solar system is and how we know that's the case thanks to radioactive decay, isotopes, half-life, and the solar nebula.

What Is Your Real Age?

Do you know how old you are? I'd tend to think that you likely do. But did you know that you are actually really old? You are billions of years old. Seriously, you really are. Particles, like protons, neutrons, and electrons, that make up your body came into existence not long after the moment of the Big Bang almost 14 billion years ago.

Talk about 40 being the new 20. This is more like a gazillion being the new nanosecond in that respect because your legal age is tiny compared to the age of the matter that makes you who you are. Whatever. The reason I tell you that is because the solar system is just like you in that sense, in that it came to be because of a sequence of events and fundamental particles that came about thanks to the Big Bang.

While technically the age of the solar system is about 4.6 billion years, its basic components were born long before then. Since other lessons explain the birth of the solar system's basic components, let's find out how scientists were able to figure out the legal age of the solar system in this lesson.

The Solar System and Solar Nebula

The solar system is the sun along with all the planets, moons, asteroids, and meteoroids held by the sun's gravitational field. Astronomers believe that the planets and the sun formed from the solar nebula, which is a cloud of interstellar gas and dust that condensed to form the entire solar system, including the sun and planets.

If this is truly the case, then you can realistically expect that the sun and the planets should be just about the same age. You know, if you were to plant a tree and a bush at the same time, sure, they may look different in size and shape after a while, like the planets and the sun vary in size and shape, but they all sprouted at about the same time nonetheless. Don't let looks deceive you.

Half-Life & The Age of the Solar System

Consequently, if scientists can get their hands on samples of material from places like the Earth, moon, Mars, and meteorites, they can, by extension, determine the age of our entire solar system even if they can't get a sample from everywhere. Additionally, these same scientists can compare the numbers they get between these samples to see if they come about to be around the same age. We'd expect the age should be similar if our hypothesis about how the solar system was formed is actually correct.

And what do you know? That's exactly what these scientists did. They analyzed radioactive elements found in rocky bodies that are part of Earth and collected from the moon and elsewhere to determine the age of the solar system.

These radioactive elements are incorporated into a rock as it solidifies. This is sort of like if you were to put some dirt into water, mix it around, and then put that into the freezer. The dirt would become part of the ice block that has solidified, and it can be analyzed at a later time.

Some of the elements incorporated into these rocks have radioactive isotopes, which are variations of an element that have the same number of protons but different numbers of neutrons. Because they are radioactive, they decay into other isotopes with time.

For instance, a parent isotope, like potassium-40, will decay into a daughter isotope, like calcium-40 and argon-40. The time it takes for half of the atoms in the parent isotope to decay into the atoms of the daughter isotope is termed a half-life. We can put this in a simple, albeit not entirely accurate, metaphor: if it takes 1 hour for half of the ice to melt, or decay, into water, the half-life of the ice is thus 1 hour.

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