How to make an exciting, erupting prehistoric tar pit: 2 simple STEM activities in 1

Sticky, dangerous quicksand or tar would be scary for any dinosaur, but how scared would they be if the tar started erupting? Let your child have some imaginative, empathetic, sensory play while learning some basic principles of chemistry with this erupting prehistoric tar pit. All you need are some basic household ingredients – and some dinosaurs, of course!

Sticky, dangerous quicksand or tar would be scary for any dinosaur, but how scared would they be if the tar started erupting? Let your child have some imaginative, empathetic, sensory play while learning some basic principles of chemistry with this erupting prehistoric tar pit. Try this simple, fun, two in one STEM activity to promote your child’s learning through play. All you need are some basic household ingredients – and some dinosaurs, of course!

Patti's new activity: pink watercolour parasaurolophus with turquoise heart, logo for dinosaur activities

Patti’s New Activity

Name: Erupting prehistoric tar pit

Activity: Make and play with a non-Newtonian substance and then experience an acid-base reaction

Dinosaurs: Whatever you fancy

Best for: A quiet afternoon of play and discovery, STEM teaching

Ease: Very – just be sure to leave some time for cleanup.

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Ankylosaurus emerging from the erupting prehistoric tar pit

What are prehistoric tar pits?

Tar pits are sometimes referred to as asphalt pits form when crude oil (decayed organic matter) is subject to pressure underground. The crude oil seeps through fractures and porous sedimentary rock layers to pool at the surface. Some light hydrocarbons (methane, ethane, propane and butane) in the crude oil evaporate leaving a black, sticky asphalt which functions and an animal trap. Tar pits will therefore often contain large fossil collections.

Notable tar pits include:

  • La Brea Tar Pits in Southern California, which have trapped and preserved animals and plants for the past 50,000 years.
  • Carpinteria Tar Pits in Carpinteria, California, formed during the Pleistocene.
  • Binagadi Asphalt Lake in Azerbaijan, which is particularly famous for the cave lion fossils found there.
  • Pitch Lake in Trinidad and Tobago, the largest deposit of solid bitumen on Earth.

The fossils found in tar pits are well preserved because they are buried rapidly after the animal’s death and protected from weathering, fungi and bacteria. While these tar pits have been a treasure trove of prehistoric fossils – more than one million bones have been recovered from the La Brea Tar Pits since 1906 – none of these fossils (so far) have been dinosaur fossils.

It is debatable whether tar pits existed during the times of dinosaurs, however, sticky mud or quicksand did exist during those periods. Quicksand would do the same thing to dinosaurs. Such dinosaur death traps have been found in the Cleveland Lloyd Dinosaur Quarry, the densest concentration of Jurassic dinosaur bones ever found, and in the Gobi Desert in China, which has revealed a treasure trove of fossils of dinosaurs that lived 230 to 145 MYA.

Experimenting with our prehistoric tar pit

Some simple chemistry

What is oobleck?

Our Little Dinosaur Aficionado first learnt about oobleck from Emily’s Wonder Lab on Netflix. The fact that we were going to make a dinosaur version of it had her roaring with anticipation.

Oobleck is a substance that can mimic the qualities of a solid or a liquid. It is a pressure-dependent substance that changes its viscosity (thickness) when pressure is placed on it. This and similar substances such as Silly Putty or quicksand are non-Newtonian fluids. In contrast, Newtonian fluids have constant viscosity, like water.  

Oobleck got its name from a book by Dr Seuss, called Bartholomew and the Oobleck.

Parasaurolophus covered in oobleck slime from our prehistoric tar pit

What is a double displacement reaction?

When the baking soda(an alkaline substance) in the oobleck and the vinegar (acid) are mixed, a chemical reaction occurs – two reactions actually.

The first reaction between these two is an acid-base reaction. The hydrogen ions in the vinegar react with the sodium and bicarbonate ions to form carbonic acid and sodium acetate.

The second decomposition reaction occurs almost immediately. The carbonic acid formed from the acid-base reaction decomposes to form water and carbon dioxide gas. This gas rises to the top of the mixture, creating bubbles that make it look like the tar is erupting. This is also the reason why baking soda and vinegar are often used to make science-project volcanoes explode.

Watching and encouraging the reaction in our erupting prehistoric tar pit

Recreating a prehistoric tar pit, with eruptions

This activity draws on the properties of oobleck to reenact a tarpit and the way dinosaurs and other prehistoric animals became trapped in prehistoric tar pits and quicksand.

Let your little dinosaur fan play with the oobleck, feel it, squeeze it, and let their toy dinosaur walk on the ‘tar’ before getting stuck in it and sinking. They will experience how quicksand and tar work, that they can seem solid and still be liquid, making escape difficult. The speed with which the dinosaurs sink will also give them an appreciation of how well-preserved the fossils in tar pits and quicksand are.

The food colouring used to make the oobleck look like tar can stain; use a plastic container, try this activity outside and have your little dinosaur fan wear an art smock or at least old clothes. Even with these precautions, your child is likely to have stained hands for a few hours after experimenting with a prehistoric tar pit. If you are worried about stained skin, use some washable liquid watercolour paint instead.

The second part of the fun builds on the acid-base reaction to create scary eruptions in your prehistoric tar pit (and will help make it easy to clean). Using a squeeze bottle for controlled spray, let your little dinosaur fan see what happens when the vinegar comes in contact with the tar. How do the dinosaurs react?

A squeeze bottle makes it easier to control the amount of vinegar. Vinegar is acidic and will burn if it comes into contact with the eyes. If your child is not good at following instructions and safety rules, make sure they wear some safety goggles. It can also irritate the skin: have your child wear rubber gloves (or equivalent) if they want to put their hands in it.

Stegosaurus emerging from the erupting prehistoric tar pit
An erupting, prehistoric tar pits

Erupting prehistoric tar pit

Yield: 1 portion of oobleck
Prep Time: 3 minutes
Active Time: 1 hour
Total Time: 1 hour 3 minutes
Difficulty: Simple

Mix up a tricky, sticky oobleck tar pit for sensory play. When your child is ready, add the vinegar and watch it react!

Materials

  • 2 cups cornflour
  • 2 cups of baking soda (bicarbonate of soda)
  • 2 tbsp cocoa powder
  • 1 1/2 cups water
  • White wine vinegar

Tools

  • Measuring cup
  • Plastic container
  • Tablespoon
  • Toy dinosaurs
  • Squeeze bottle
  • Art smock
  • Safety goggles
  • Gloves

Instructions

To make the oobleck tar pit What you need to make this prehistoric tar pit

  1. Combine the baking soda, cornflour and cocoa powder in a large container (suitable for play). Mix the dry ingredients
  2. Add the water, little by little, and mix with your hands until the mixture is mud-like, but not runny. Slowly add the water and mix until you have a slime consistency
  3. Add the dinosaurs and let the fun begin!

To make the tar pit erupt

  1. Once your little dinosaur fan has had enough of a play, give them a squeeze bottle filled with vinegar and let them squeeze some into the mud to see the eruptions!

Notes

The tar can only be used once and should not be stored, especially once the vinegar has been added to it.

If your child wants to put their hands in the erupting slime (most do), put some rubber gloves on them as any unreacted vinegar can sting if they have any cuts or scrapes on their hands.

We had to take a brief break between the two phases and came back to find that the oobleck was quite hard. We had to add more water and mix again to get back our mud consistency before continuing.

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Simple sensory play – with dinosaurs!

The changing nature of oobleck and the bubbles formed with vinegar is added make this a wonderful STEM activity to try at home. All you need is some basic household ingredients and some dinosaurs for hours of fun and learning.

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