• Question: How do fossils form

    Asked by area492par to Richard B, Michael S, Martin M, Liam H, Kirsty R, Eleftheria S, David B, Alexander dB on 30 Jan 2024.
    • Photo: Eleftheria Stavridou

      Eleftheria Stavridou answered on 30 Jan 2024:

      It all starts with a plant or animal. When they die, their remains, like bones, shells, or even leaves, can end up on the ground or at the bottom of a body of water. To become a fossil, these remains need to be buried quickly. This can happen in various ways, like being covered by sediment (dirt, sand, or mud) during a storm, or sinking to the bottom of a lake or ocean.
      Over time, more and more sediment accumulates on top of the remains. As the layers pile up, they create pressure, kind of like pressing down on a sandwich. This pressure helps to harden the sediment into rock.
      The buried remains are now surrounded by rock. Minerals from the water can seep into the bones or plant tissues, slowly replacing them with hard minerals and turning them in rocks.
      Millions of years later, erosion (wind, water, or even people digging) can expose the fossils. Sometimes, fossils are found in cliffs, rocks, or even in the ground.

    • Photo: David Bremner

      David Bremner answered on 31 Jan 2024:

      i think it is once an organism has died and gets buried by soil or other layers it decomposes and any soft tissue effectively dissolves and leaves the hard parts like the skeleton. As time passes more and more layers form round this and pushes down on it, and the layers around the skeleton turn to rock. Water from the earth seeping through this and the pressure of all the layers pushing down on it eventually dissolves the skeleton and minerals from the water replace the bone leaving behind a rock replica of the original.

    • Photo: Martin McCoustra

      Martin McCoustra answered on 31 Jan 2024:

      Most fossils were basically bones originally. The soft organic materials that hold the bones together are gradually replaced by minerals that convert the bone to stone… the classical fossil. This takes a long time. Sometimes when the animal or plant is buried in soft mud, we can see an imprint of the softer material covering the bones.. like scales or feathers.

      If you want to see fossilisation in action there are limestone caves around the world where if you hang up an object in water dripping from the ceiling of caves, the object becomes coated in limestone in a relatively short time.

    • Photo: Liam Herringshaw

      Liam Herringshaw answered on 31 Jan 2024:

      If an animal or plant or microscopic organism (or a structure they have made such as a burrow, a footprint, or some poo) gets buried by sediment, and that sediment gets buried by more sediment, and squished, and compacted, and mineral-rich waters move through the sediment, and fill in the spaces between the grains, and inside the tissues of the organism, with the minerals, and these glue the grains or tissues together, and cement them, and the layer of sediment turns to stone, a fossil may be formed. Then, after having been buried a long way below the surface, if the rock is then slowly forced back towards the surface by forces within the Earth’s crust, the fossil might be brought back towards the light again, and a lucky person might one day walk along and spot it in the rock, and try to tell its story.

      For a more entertaining description, watch The Fossil Song: https://www.youtube.com/watch?v=1NRGAhRZ9cM!

    • Photo: Kirsty Ross

      Kirsty Ross answered on 31 Jan 2024:

      You’ve got some excellent answers from the other scientists here. The only thing I’d add is that fossil formation is rare. We also don’t know what fossils we may have lost due the tectonic plates that make up the surface of the planet moving around. Rocks are being destroyed and created all the time at the boundaries between plates, and these aren’t great places to be if you are a fossil!

    • Photo: Michael Schubert

      Michael Schubert answered on 31 Jan 2024:

      Everyone has given you really good answers on how fossils form, so I don’t need to add much there! But we do sometimes learn more about ancient plants and animals because we find their actual bodies or parts preserved, instead of just the fossilized parts. This can happen when they get trapped in a soft substance, like tree sap (which turns into amber) or mud (which turns into rock); we also sometimes find them in tar pits or frozen in ice. When we find something like that, we can learn things about their skin or organs that we might not find out from fossilized bones and shells, so it’s always an exciting day!

    • Photo: Richard Birch

      Richard Birch answered on 1 Feb 2024:

      Nearly always in water.
      When something dies and sinks to the bottom of the sea, preferably where there is less oxygen and no scavengers, then it will be buried by sediment. The quicker this happens, the better the fossil will be preserved. Normally its a slow process, so only the hard parts like shell, bone and teeth don’t decay and get buried. Over time, the sediment hardens into rock with the fossil preserved in it. This process is called TAPHONOMY (taff-on-o-mee). In exceptional cases, where a mudslide or volcanic eruption buries things quickly in a deep layer of sediment or ash, even the soft parts don’t decay and become preserved.
      But remember, the fossil will be replaced by minerals, even when its an insect in amber. No part of the actual animal remains, so you won’t be able to extract DNA from a mosquito and clone a dinosaur like in Jurassic Park. Never say never, though…

    • Photo: Alexander de Bruin

      Alexander de Bruin answered on 1 Feb 2024:

      The other scientists have completely covered this, so I won’t add more detail, rather a cool piece of science I’ve encountered for looking at fossils. One of the big challenges with inspecting fossils and getting the most information out of them is the process of getting them out of the rock in which they are embedded. I’ve seen some research where scientists were using high-power x-rays to scan the fossil while it was still in the rock and they were able to get a beautiful 3D image of the fossil without any damage to it at all. We actually use this technique, called X-Ray Microscopy or Computed Tomography, to look at many things, from catalysts to engine parts to fossils to bits of living people!