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Layers of Rocks give us clues to their age

When rocks occur as undisturbed layers, we find that the lowest layers will be the oldest and topmost layers will be the youngest. Frequently rivers cut incisions into the earths's surface and expose such layers. The Grand Canyon in the U.S.A. is the deepest cleft on the earth's surface.

Grand Canyon from Moran Point

The Grand Canyon, Western United States of America

The upper rocks of this canyon are about 200 million years old and contain traces of reptiles, impressions of fern leaves and wings of insects. Halfway down the canyon you find limestone of about 400 million years old which contains the remains of primitive armoured fish. Further down the canyon there are no traces of vertebrates. Three-quarters way down there are no apparent traces of life. Close to the bottom of the canyon the rocks are more than 2 000 million years old.

A model of Dunkleosteus telleri a highly evolved Placoderm which were armoured and jawed fish. Instead of actual teeth, Dunkleosteus possessed two long, bony blades that could slice through flesh and snap and crush bones and almost anything else. It was a vicious hunter, and probably ate whatever it could find, including sharks.

Rocks as old as those of the bottom of the Grand Canyon have been found to contain a fine-grain flint-like substance called chert. Contained in this chert are simple organisms some of which resemble algae filaments others resemble bacteria.

Chert similar to that found at the bottom of the Grand Canyon

These were thought to be until recently the earliest known organism (see further down and for a time-line of life go here) and are referred to as cyanobacteria or blue-greens. These organisms are able to extract hydrogen from water and thereby produce oxygen which is essential for other organisms to survive. The chemical agent responsible for this process is called chlorophyll and process is called photosynthesis, and occurs in true algae and higher plants.

Anabaena sphaerica

The Anabaena is a genus of filamentous- cyanobacteria, or blue-green algae, found as plankton. It is known for its nitrogen fixing abilities, and they form

Pre-Cambrian- stromatolites in the Siyeh Formation, Glacier National Park. In 2002, William Schopf of UCLA published a controversial paper in the scientific journal: Nature arguing that geological formations such as this possess 3.5 billion year old fossilized- algae microbes.

Recent News: Original article

Minik & Frei (2004) wrote a paper that concluded that "Planktonic organisms lived in the Isuan oceans where they produced large amounts of highly 13C-depleted organic matter. The aquatic environment of these organisms comprised relatively oxidized compartments, which allowed solute transport of U. The high biomass productivity of planktonic organisms, the strongly 13C-depleted carbon isotopic signature and the evidence for the presence of oxidized aquatic environments all suggest that oxygenic photosynthesis had developed before 3700 Ma."