Rights: The University of Waikato Published 10 June 2008 Download

By looking at fossils, Adam Vonk can determine two things. Firstly, he can work out how old the rocks are, and secondly, he can work out the paleoenvironment of the rock. Paleoenvironment refers to the ancient environment that the fossil formed in.

By looking at one family of organisms and tracing how they have changed or evolved over time, it is possible to work out the approximate age of the rock. For his research, Adam looks at scallops. He knows if he finds a scallop shell in the rock that existed 10 million years ago, then the rock must be around that age. If he finds another scallop shell that existed five million years ago, that the older one evolved into, he knows that the rock must be younger.

To work out paleoenvironments, scientists work on the basis that the Earth back in time was similar to how the Earth is today. Adam reconstructs paleoenvironments by looking at the rock the fossil is in and asking: Where would this organism have been at the time of fossilisation? What would be a current environment we can find on the planet now that would be similar?

Points of interest

Discuss the environment where we can find scallops today.


Fossils allow me to do essentially two main things – working out the relative age of the rocks and the paleoenvironment of the rocks, so what the conditions of deposition of that rock were. So certain lineages of fossils have evolved over time, so in my case, in my field area, we have a series of scallops or pectens as they are called. They have… they have actually evolved over time, so back at about say 10 million years ago, we had one species of fossil called Sectipecten grangei. Now, that was quite a small scallop with quite large ribs on it. They have actually evolved into one called Sectipecten wollastoni, and so we get a whole lineage of these scallops and, depending on which one we find in any particular rock, can tell us how old that rock is.

To work out the environment that the rock was deposited in, we call that the paleoenvironment. We use a principle that what the Earth was like back in time is similar to what it’s like today. Say we find a scallop way in the hill country of Taranaki and we know that similar scallops today accumulate in a sort of offshore sandy environment, then we know that that rock sitting up on the hill actually was sitting in a sandy sort of open shelf environment, millions of years ago.

So it’s… it’s reconstructing the paleoenvironments from similar observations that we make today around the modern NZ coast.