Shop Windows to the Universe

Young Voices for the Planet DVD in our online store includes 8 films where students speak out and take action on climate change.

Click on image for full size
Image from: Kentucky Coal Education Web Site

Iron Ore Deposits

Eventually, as with the development of photosynthesis along sulfur and methane pathways, where sulfur and methane products are produced, photosynthesis along the oxygen pathway, where oxygen is produced, came into being.

One important thing to know about oxygen is that it is very reactive. It is one of the most reactive of all the elements in nature. This means that it will readily attack and attach itself to other elements. In particular, iron, sulfur, and manganese are readily attacked by oxygen.

As molecular oxygen began to be produced by early autotrophs, a curious phenomena occured. Large amounts of iron which had accumulated in the early ocean as both FeSO4- and a solid FeS2 (pyrite) from naturally occuring weathering and as a product of heterotrophic activity, were attacked by the accumulating O2. As O2 reacts with FeS2 (pyrite), Fe2O3 (limonite) is produced. When O2 reacts with FeSO4-, Fe2O3 (hematite) is produced. These rocks, along with magnetite (Fe3O4 - a magnetic rock) and siderite (FeCO3), are also called iron ores. Oxide rocks such as these are mined today, and the iron (Fe) they contain is extracted.

Over a period of a billion years, huge deposits of iron ores were laid at the bottom of the sea. This activity took place between 3.5 and 2.5 billion years ago. Iron ores mined today in the United States, Australia, and South Africa, are part of the huge deposits laid down at that time. Once the oceans were swept clean of iron, then the oxygen could begin to accumulate in the atmosphere, and respiration by sophisticated life forms could begin in earnest. It took a billion years for this process to complete. When it was finished, it closed the period in the history of the Earth which we call the Archean .

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!

Windows to the Universe Community



You might also be interested in:


Photosynthesis is the name of the process by which autotrophs (self-feeders) convert water, carbon dioxide, and solar energy into sugars and oxygen. It is a complex chemical process by which plants and...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

Early Life

Organisms that are able to make their own food (in the form of sugars) by using the energy of the Sun are called autotrophs, meaning "self-feeders". Photosynthesis is the name of the process through which...more

Salts included in the Earth's early ocean

We all know that salt is a big part of the ocean water today. Two things help scientists figure out what chemicals may have been part of the Earth's early oceans. Igneous rocks are made of iron, aluminum,...more

The First Living Cells

The first beings were probably much like coacervates. As a group, these bacteria are called heterotrophic anaerobes. Because there was virtually no oxygen in the atmosphere at this time, these bacteria...more


Respiration is the name of the general process by which living organisms convert sugars and oxygen into biochemical energy. The process occurs in all organisms, including animals, plants, fungi, and bacteria...more

Pre-Cambrian Life

About 2.5 billion years ago (BYA), after the iron in the ocean was gone to form iron ore deposits, oxygen began accumulating in the atmosphere. Soon, enough oxygen accumulated in the early atmosphere for...more

The Archean

The Archean is the name of the age which began with the forming Earth. The duration of the Archean, 2.8 billion years, is more than half the expected age of the Earth. We don't know much about this period,...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA