Weathering and the Early Rock Cycle

الأحد مايو 17, 2015 4:32 pm

Weathering and the Early Rock Cycle

Three billion year old sedimentary rocks form the top part of the

Barberton Supergroup. The rock is about 2.5 km thick. These rocks

indicate that Earth’s young, very small continents were subject to

weathering and erosion. At this time, there was no soil or plants on land.

The atmosphere had yet to develop free oxygen. It was mostly water

vapor, carbon dioxide, and nitrogen. The atmosphere back then was more

powerful at decomposing rocks than today. The surfaces of the young

continents were rapidly stripped of weathered particles. Rains washed

their rocky surfaces. Sediment was transported by rivers. It was deposited

around the edges of the continents. Coarse sediments were deposited in

shallower water. They formed conglomerates and sandstones. Ripples and

bedding structures also formed. They were similar to those seen in the

ocean today. Finer sediments were transported into deeper water. They

formed mudstones. These rocks indicate that the rock cycle was in full

operation more than 3.5 billion years ago.