Precambrian Facts & Information: The Birth Of A Planet And The First Life On Earth

The Precambrian began with the birth of Earth and saw the formation of the moon, the creation and breaking up of supercontinents, the first oceans, the introduction of oxygen into the atmosphere, and the appearance of life on Earth.

Read on for Precambrian facts and information…

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What Is The Precambrian?

The Precambrian encompasses Earth’s history from the planet’s formation around 4.6 billion years ago to the start of the Phanerozoic Eon, around 541 million years ago (mya). The Precambrian therefore accounts for around 88% of all of Earth’s history.

In the geologic time scale, Earth’s history is divided into four eons: the Hadean Eon, Archean Eon, Proterozoic Eon and Phanerozoic Eon.

The term “Precambrian” refers to Earth’s history prior to the Cambrian Period. The Cambrian Period is the first period of the fourth eon, the Phanerozoic Eon. Therefore, the Precambrian includes all that occurred in the Hadean, Archean, and Proterozoic eons.

The Precambrian was once thought to be devoid of all life because no visible fossils were found in Precambrian rocks.

However, with the advent of micropaleontology (the study of fossils too small to be seen by the naked eye), scientists now believe that simple forms of life may have existed even in the Hadean, the earliest Precambrian eon. By the end of the Proterozoic Eon, multicellular life had appeared.

The Hadean Eon

  • ~4600 – 4000 Mya

Hadean Eon
A volcano erupting on Hawaii gives us an idea of what Earth may have been like in the Hadean Eon. Photo by Marc Szeglat on Unsplash

The Hadean Eon began with the formation of Earth, some 4.6 billion years ago.

The Earth, and the other planets in the Solar System, are thought to have been formed by the congregation of dust and gas left over after the formation of the sun.

Initially, Earth’s surface was unstable and partly molten. The Hadean Eon was named after Hades – the underworld of Greek Mythology.

Early on in the Hadean Eon, Earth is thought to have collided with a Mars-sized planet known as Theia. The resultant debris from this collision is thought to have formed the moon.

This explanation for the formation of the moon is known as the “Giant-Impact Hypothesis”. If correct, it means that at the beginning of the Hadean Eon, there was no moon.

Very few rocks from this eon are found on Earth, but meteors from space, and rocks from the moon, are as old as the Hadean Eon.

As the Earth cooled, its crust formed, along with seas of liquid water and an atmosphere which consisted mostly of water vapor and carbon dioxide gas.

For many years scientists believed that life on Earth first appeared during the Archean Eon. However, analyses of zircon crystals in Australia – the oldest-known remnants of the Earth’s crust – reveal carbon minerals. These are thought to be evidence that simple living organisms existed in the Hadean Eon.

The Archean Eon

  • 4000 – 2500 Mya

Archean Eon
During the Archean Eon at least one supercontinent formed. Photo by Toby Elliott on Unsplash

Eras of the Archean Eon

  • Eoarchean (4000 to 3600 Mya)
  • Paleoarchean (3600 to 3200 Mya)
  • Mesoarchean (3200 to 2800 Mya)
  • Neoarchean (2800 to 2500 Mya)

Until traces of life in zircon crystals from the Hadean Eon were discovered, life was believed to have first appeared during the Archean Eon.

The presence of very early life forms, such as primitive bacteria, blue-green algae and other single-celled microbes marks the start of the Archean Eon.

Fossil evidence of these simple life forms first appears in rocks dated about 3.5 mya. At this time, the atmosphere consisted mainly of nitrogen; there was little or no free oxygen (O2). Free oxygen, which is oxygen in its most common form, is formed during photosynthesis.

Chains of islands, as well as rocky plates, occurred where active volcanoes had thrown up lava, and between these rocky outcrops lay shallow seas. During the Archean Eon, one or more supercontinents is believed to have formed.

The earliest-known rock formations on Earth date from the Archean Eon.

During the Archean Eon, the sun was up to 30% less intense as it is today.

The Proterozoic Eon

  • 2500 – 541.0 ± 1.0 Mya

Earth during the Proterozoic Eon may have resembled Antarctica
Earth during the Proterozoic Eon may have resembled Antarctica. Photo by Matt Palmer on Unsplash

Eras and Periods of the Proterozoic Eon

Paleoproterozoic Era 2500 to 1600 Mya

  • Siderian 2500 to 2300 Mya
  • Rhyacian 2300 to 2050 Mya
  • Orosirian 2050 to 1800 Mya
  • Statherian 1800 to 1600 Mya

Mesoproterozoic Era (1600 to 1000 Mya)

  • Calymmian 1600 to 1400 Mya
  • Ectasian 1400 to 1200 Mya
  • Stenian 1200 to 1000 Mya

Neoproterozoic Era (1000 to 541.0 ±1.0 Mya)

  • Tonian 1000 to ~ 720 Mya
  • Cryogenian ~ 720 to ~ 635 Mya
  • Ediacaran ~ 635 to 541.0 ±1.0 Mya

Near the beginning of the Proterozoic Eon, volcanic islands and vast rocky plates clustered together to form the supercontinent Columbia.

Over the course of the Proterozoic Eon, Columbia split up, and its fragments reassembled to form the supercontinent Rodinia.

Throughout much of the Proterozoic Eon, Earth was very cold and the land was covered by glaciers. Many scientists believe that, towards the end of the Proterozoic Eon, the entire surface of Earth may have been frozen; a hypothesis known as “Snowball Earth”.

The Great Oxidation Event occurred during the Paleoproterozoic Era, the first era of the Proterozoic Eon. During this time the amount of oxygen in Earth’s atmosphere and oceans greatly increased. This allowed many different types of organism to rise and flourish.

During the Proterozoic Eon, single-celled lifeforms continued to evolve. During the Ediacaran Period, the final period of the Proterozoic Eon, the first multi-cellular organisms appeared.

Rangia, a multicellular organism with leaf-like fronds that lived on the sea bed in the Ediacaran Period, was the first Precambrian fossil to be found that is not microscopic. It, and the other characteristic organisms of the period, such as the slug-like Kimberella, are known collectively as the Ediacaran biota.

The characteristic organisms of the Ediacaran Period are known as the Ediacaran biota.

By the end of the Proterozoic Eon, the atmosphere was rich in free oxygen. The scene was set for the Cambrian Explosion – the sudden and explosive diversification of living things that occurred at the beginning of the Paleozoic Era.

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