Precambrian Facts: 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…

Further Information On Active Wild

Geologic Time Scale With Facts And Examples: What Is It & What Is It Used For?
The Triassic Period Facts For Kids & Adults: The Ultimate Guide to the First Period of the Mesozoic Era.
The Jurassic Period Facts: The Ultimate Guide To The Second Period Of The Mesozoic Era
The Cretaceous Period Facts: The Ultimate Guide To The Third & Final Period Of The Mesozoic Era

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

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

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

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.