Ripple Marks

Ripple marks in sand are commonly observed to form in shallow water near the shores in modern beach environments.

Finding ancient equivalents of modern ripple marks in sandstone suggests that the rock formed in a similar environment millions of years ago.

See also: Rocks - Sedimentary Stuctures

Mud Cracks

Modern day mudcracks form in fine clay material that was deposited in shallow water but has dried out.

Similarly shaped mudcracks are preserved on the surface of an ancient mudstone, suggesting that the sediments once dried out beneath the air and were thus deposited on land.

See also: Rocks - Sedimentary Structures


A conglomerate is a clastic sedimentary rock that formed from coarse sediments of rounded pebbles typically deposited in stream environments. At present we observe that the rounded pebbles are a product of intensive abrasion during prolonged transportation in water.

See also: Sedimentary Rocks

A 2700 million year old conglomerate from Witwatersrand, South Africa, with rounded pebbles gives evidence that water and streams were already present on the early Earth surface during Archean time.

See also: Archean - The Earliest Atmosphere and Hydrosphere