Timeline of Earth

This timeline of Earth's history shows important geological and biological events from the formation of the Earth to the arrival of modern humans. It helps us learn how our planet has changed over billions of years. Times are listed in millions of years, or megaanni (Ma).

Earth began about 4.5 billion years ago, forming from dust and rocks in space. Over time, it cooled, formed oceans, and developed an atmosphere that allowed life to begin. Very simple organisms, like bacteria, were the first life forms.

As millions of years passed, life became more complex. Plants and animals appeared in oceans and eventually on land. Big events, such as floods and the movement of continents, changed Earth's surface and affected the kinds of life that could survive.

Finally, around 200,000 years ago, modern humans appeared. Studying this timeline helps scientists learn about our past and guess what might happen in the future. For a deeper look, see the History of the Earth and Geological history of Earth. For earlier events, see the Timeline of the early universe. You might also be interested in the Geologic time scale and the Timeline of the evolutionary history of life.

Dating of the geologic record

The geologic record is the strata (layers) of rock in the planet's crust. Geologists study these layers to learn about Earth's history. They use a method called radiometric dating to find the age of very old rocks. This method measures the decay of radioactive elements like carbon-14 and potassium-40 into other elements.

Carbon-14 helps date objects up to about 50,000 years old, such as wood, charcoal, paper, fabrics, fossils, and shells. For older rocks, scientists use the potassium-argon dating method. They also study fossils to find the ages of more recent rock layers. These fossils show important changes, like when dinosaurs disappeared or when new species, like hominids, appeared.

The earliest Solar System

Main articles: Formation and evolution of the Solar System and Nebular hypothesis

In the very beginning of our Solar System, the Sun, small objects called planetesimals, and the giant planets came into existence. The inner part of the Solar System, where Earth is, took longer to form than the outer parts, so Earth and our Moon did not exist yet.

Around 4,570 million years ago, a huge star explosion called a supernova spread heavy elements into space. These elements later became part of Earth. Shortly after, a cloud of hydrogen collapsed to form our Sun. A spinning disc of dust and gas formed around the young Sun, and from this disc, Earth began to take shape. During this time, Earth was very young and bumped into many space rocks, which helped it grow larger.

Precambrian Supereon

Main article: Precambrian

The Precambrian lasted from about 4,533 million years ago to 539 million years ago. It makes up about 85% of Earth's entire history. This long time is split into three main parts called eons: the Hadean, Archaean, and Proterozoic. During this time, Earth formed and changed, and the first creatures with hard outer parts appeared.

Hadean Eon

Main article: Hadean

The Hadean Eon is the time when Earth began, about 4,533 million years ago. During this time, the Earth and the Moon formed, perhaps from a collision with a planet named Theia. After this, Earth was covered in hot, melted rock, and its air was filled with gases like methane, nitrogen, and water vapor.

By around 4,450 million years ago, the Sun became steady, and space debris near Earth cleared away. The first solid skin of rock formed on both Earth and the Moon, and Earth's surface cooled enough for oceans to show up. The oldest known mineral, found in Western Australia, comes from this time, proving that liquid water existed. Signs of the earliest life have been found in these very old rocks, hinting that life might have started quickly on our planet.

Archean Eon

Main article: Archean

The Archean Eon is the earliest time in Earth's history. It lasted from about 4 billion to 2.5 billion years ago. During this time, Earth's first continents formed. The first signs of life also appeared.

Important events from this time include the formation of the first landmasses, the first simple life forms, and big changes in Earth's air and water. Early life was tiny and lived in water. Over time, these tiny organisms changed the air by making oxygen. This helped more complex life forms develop later.

Proterozoic Eon

Main article: Proterozoic

The Proterozoic Eon, from about 2500 million years ago to 539 million years ago, was a time of big changes for Earth. This period saw the first signs of life, like bacteria and algae. Earth's air and water also changed a lot during this time.

Paleoproterozoic Era

Main article: Paleoproterozoic

The Paleoproterozoic Era began with big changes, such as more oxygen appearing in the air. These changes affected the living things on Earth. Many important rocks formed, and big cold periods shaped the land.

Mesoproterozoic Era

Main article: Mesoproterozoic

In the Mesoproterozoic Era, the continents kept moving, and new land shapes appeared. This time also saw life becoming more complicated.

Neoproterozoic Era

Main article: Neoproterozoic

The Neoproterozoic Era had big climate shifts, including very cold times called "Snowball Earth" events. Even with these tough conditions, life kept evolving, leading to the first complex animals and big changes in Earth's plant and animal groups.

Phanerozoic Eon

Main article: Phanerozoic

The Phanerozoic Eon is a time in Earth's history that started about 539 million years ago and is still going on. It is when many complex life forms appeared, like animals and plants we know today.

During this time, there were several important changes in life on Earth. The Paleozoic Era was when many different sea creatures appeared and the first animals walked on land. The Mesozoic Era is known for the time when dinosaurs lived and ruled the land, sea, and sky. The Cenozoic Era is called the age of mammals, including the rise of primates and eventually humans. Each period brought new species and big changes to Earth's nature, shaping our world today.

Etymology of period names

The names of Earth's geological periods come from places where scientists first studied the rocks. For example, the Jurassic period is named after the Jura Mountains in France. These names help us remember Earth's long history.

Visual summary

The image shows the history of nature from the Big Bang to today. Important events are marked on a spiral. Each full turn of the spiral is one billion years. The last 500 million years are shown in more detail to point out recent changes.