Shortcut Navigation:
An Evolving Atmosphere

An evolving atmosphere

An evolving atmosphere

  • Exhibition Text

    • About 1.7 billion years ago, banded iron formations — sedimentary rocks consisting of iron-rich layers alternating with iron-poor ones — stopped forming. By this time, photosynthesis had supplied enough oxygen  to entirely deplete the oceans of their iron. With no more iron available to remove the oxygen, the gas slowly began to accumulate in the atmosphere, increasing to perhaps 2 percent near the end of the Precambrian (560 million years ago), and eventually to its present level of 20 percent.

      Rocks the reveal conditions of early Earth

       

      Clues to the conditions on the early Earth are found in rocks like the Huronian Supergroup, a set of sedimentary rock formations, up to 12 kilometers thick, laid down between 2.5 and 2.2 billion years ago. The rocks are exposed just north of Lake Huron, Canada. Many geologists believe that this sequence of rocks records a change from an oxygen-free to an oxygen-bearing atmosphere.

       

      Show more
  • For Educators

    • Topic: Earth Science

      Subtopic: Climate/Climate Change

      Keywords: Atmosphere, Geology, Stratigraphic--Huronian, Huron, Lake (Mich. and Ont.), Life (Biology), Life--Origin, Oxygen, Paleoclimatology, Photosynthesis, Sedimentary rocks

In This Section

An Evolving Atmosphere

Rocks that reveal conditions of early Earth

Clues to the conditions on the early Earth are found in rocks like the Huronian Supergroup, a set of sedimentary rock formations, up to 12 kilometers thick, laid down between 2.5 and 2.2 billion years ago.

Gray-White Quartz

Gray-white quartzite

This quartzite formed in a riverbed, as indicated by the well-developed cross-bedding (sedimentary layers at angles to the main horizontal layers).

Icebox or Hothouse?

Icebox or hothouse?

By observing other stars, we think that the Sun’s luminosity has increased by 25 percent since its formation.

Red Quartzite

Red quartzite

The rocks in the upper part of the Huronian Supergroup are red-brown, like this quartzite specimen.

American Museum of Natural History

Central Park West at 79th Street
New York, NY 10024-5192
Phone: 212-769-5100

Open daily from 10 am - 5:45 pm
except on Thanksgiving and Christmas
Maps and Directions