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How salty was the Precambrian ocean compared to now?(An experiment in water density)

Updated: Nov 19, 2022

This is our rainbow straw experiment. This tests water density while also looking really cool. It’s a fun experiment inspired by Steve Spangler science to try again and again as there are many factors to its success. My son was so in love with it at the end of the day he played with it like a toy dunking from one color to the next and I cooked dinner efficiently and on time. That was an added bonus, but such a much needed one. The water in the straw will slowly, slowly mix so it’s really cool to see how long you can make the rainbow ‘last’ in the tube.

Here’s what you need for the experiment

-6 jars


-Hot water

-a measuring cup

-food coloring

-a clear straw

Place all the jars next to each other and LABEL each jar with how much salt is in it. The first jar you label 2 tablespoons, the second 4 tablespoons, the third 6 tablespoons, and so on until each jar has the desired increased amount of salt in it. Ours are labeled as Pre-Cambrian for really REALLY salty waters and Really salty water.

Next, add a CONSISTENT amount of hot water to each jar. We added 1 cup of water to each jar no matter the salt.

Keeping the amount of water consistent to different amounts of salt is what effects the water density. Next, STIR LIKE CRAZY. We stirred our jars one at a time to get maximum salt absorption and we also poured our water and salt into mason jars so we could over the jar with the mason jar lid and shake them instead of stir them, as what you are going for here is maximum salt absorption in the water. Then you’ll want to add your food coloring. We started our rainbow at water with the most salt, so the jar with 12 tablespoons of salt was red, the jar with 10 tablespoons of salt was orange, and so on. Next time, we will be doing it the other way, as the blue food coloring really takes over the other colors FAST but not so fast that you can’t see the layers.

Now take your straw and dunk it DEEP into your salt water with 2 tablespoons of salt. Remove your thumb and cap it quickly, next dunk it DEEP into your salt water with 4 tablespoons of salt then remove your thumb and cap it quickly, repeat this process for your entire library of liquids you’ve created. The less dense water will be ‘pushed up’ by the greater density of the water with more density!Why does this work? Density is the measurement or study of how much stuff is packed into any given space. This is especially true of our salt water solutions, with consistent amounts of water mixed with an inconsistent amount of salt. The solutions stack because a solution with a low density will stack on top of a solution with high density. This was used to explain the saltiness of the Precambrian sea vs the Cambrian and what effectively led to the conditions for the Cambrian explosion of life Vs the jelly like creatures of the Precambrian.

If you run this experiment in your home and post it please tag me @raising.seidlings so I can see your beautiful rainbows! Thank you so much for your time and I hope your day is blessed.

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