Shop Windows to the Universe

Our Glaciers: Then and Now activity kit helps you see the changes taking place in glaciers around the world. See all our activity kits and classroom activities.

Evidence of Evolution

This table lists the unstable “parent” elements and the more stable “daughter” elements that they become. Half-lives refer to the length of time it takes for half the parent element in a rock or other object to decay. Because different elements have different half-lives, their useful ranges vary.
Click on image for full size
USGS

Leonardo Da Vinci’s Findings and the Ages of Fossils

Leonardo Da Vinci, 15th century Italian artist, scientist and inventor, was one of the first to document the types of fossils he found and noticed that different fossils were found in different rocks. He was one of the first people to recognize that fossils were the remains of living things and that the Earth must be much older than most of his contemporaries believed it to be. In the following centuries, scientists built on his ideas. 19th century scientists studied sedimentary rocks and fossils from all over the world developing an understanding of the relative ages of rock layers and fossils. They could tell that some layers were older than others, but they didn’t know how old rocks and fossils within them were. More recently, in the 20th century, scientists have developed technology to allow the numerical ages of rocks and fossils to be determined. See below for further explanation of relative and numerical ages.

  • Relative age dating of sedimentary rocks layers and the fossils they contain means establishing which rock layers are older than others. This method of dating does not give ages in years. Instead it establishes which rocks and fossils are older and which are younger. Relative age dating relies on several methods. One of the most important involves the principle that younger rock layers are formed on top of older rock layers.
  • Numerical age dating means establishing the approximate age in years of a particular layer of rock by analyzing the decay of radioactive elements. Radioactive decay occurs when an unstable form of a chemical element naturally converts to a stable form of another chemical element. Volcanic ash layers, for example, contain radioactive elements. When the ash layer forms, the radioactive elements begins to decay at a constant rate. Because we know the rates of decay of different radioactive elements, we can understand the age of the ash layer by examining the amount of unstable radioactive element and stable product element within the layer.
    Last modified May 16, 2005 by Lisa Gardiner.

    Shop Windows to the Universe Science Store!

    Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, as well as books on science education!

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Radioactive Decay

Some materials are radioactive. They emit radiation. When an atom of a radioactive substance gives off radiation, it becomes a new type of atom. This process is called radioactive decay. There are two...more

Element (Chemical Element)

An element (also called a "chemical element") is a substance made up entirely of atoms having the same atomic number; that is, all of the atoms have the same number of protons. Hydrogen, helium, oxygen,...more

ExploraTour - Looking at the World in a Different Light

Even though the sleeping man is no longer on the bed, you can still see where he was lying down. The heat from his body warmed up the bed sheets which are now radiating infrared light toward your eyes....more

ExploraTour - Looking at the World in a Different Light

All warm objects (not just people) radiate in the infrared. Warmer objects give off more infrared radiation. Very hot objects radiate other types of light in addition to infrared. Click on the picture...more

ExploraTour - Looking at the World in a Different Light

Your eye is a wonderful detector of visible light. Different frequencies of light produce different sensations in the eye which we interpret as colors. Our eyes detect light by using light sensitive components...more

ExploraTour - Looking at the World in a Different Light

Imagine you found a pair of special glasses that not only gave you telescopic vision but gave you the ability to see all forms of radiant energy. The universe in visible light contains all the familiar...more

ExploraTour - Looking at the World in a Different Light

This is a volcano on the island of Miyake in Japan. It has erupted, sending hot lava and ash into the air, a total of ten times. The time after one eruption until the next occurred was about twenty years...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF