Timeline of Earth

This timeline of Earth's history summarizes significant geological and biological events from the formation of the Earth to the arrival of modern humans. It helps us understand 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 a 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. Huge events, such as massive floods and the movement of continents, shaped Earth's surface and influenced 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 predict 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 and how it formed. 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 is useful for dating 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 help mark important changes, like when certain animals, such as 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 planet-like objects called planetesimals, and the giant planets came into existence. The inner part of the Solar System, where Earth is, took longer to form compared to 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 still very young and went through many collisions with other space rocks, which helped it grow larger.

Precambrian Supereon

Main article: Precambrian

The Precambrian, lasting from about 4,533 million years ago to 539 million years ago, makes up about 85% of Earth's entire history. This long period is divided into three main parts called eons: the Hadean, Archaean, and Proterozoic. During this time, Earth formed and evolved, eventually leading to the first creatures with hard outer parts that left behind many fossils.

Hadean Eon

Main article: Hadean

The Hadean Eon marks the very beginning of Earth's history, starting around 4,533 million years ago. This is when the Earth and Moon formed, possibly from a collision between early Earth and a planet called Theia. After this impact, Earth was covered by a deep ocean of molten rock, and its atmosphere was made of gases like methane, nitrogen, and water vapor.

By about 4,450 million years ago, the Sun became stable, clearing away space debris around Earth. The first solid crust formed on both Earth and the Moon, and Earth's surface cooled enough for oceans to appear. The oldest known mineral, found in Western Australia, dates from this time, showing that liquid water was present. Evidence of the earliest life comes from these same ancient rocks, suggesting life may have appeared quickly on our planet.

Archean Eon

Main article: Archean

The Archean Eon marks the earliest time in Earth's history, from about 4 billion to 2.5 billion years ago. During this time, Earth's first continents formed, and the first signs of life appeared. The oldest known rocks and the first evidence of water and possibly early life have been found from this period.

Key events include the formation of the first continental landmasses, the appearance of the first simple life forms, and significant changes in Earth's atmosphere and oceans. Early life was mostly microscopic and lived in water. Over time, these organisms changed the planet's atmosphere by producing oxygen, which eventually led to the development of more complex life forms.

Proterozoic Eon

Main article: Proterozoic

The Proterozoic Eon, from about 2500 million years ago to 539 million years ago, marks important changes in Earth's history. This period saw the first signs of life, including bacteria and algae, and major shifts in Earth's atmosphere and oceans.

Paleoproterozoic Era

Main article: Paleoproterozoic

The Paleoproterozoic Era began with significant events like the rise of oxygen in the atmosphere, leading to changes in life forms. Important geological formations and glaciations shaped the continents during this time.

Mesoproterozoic Era

Main article: Mesoproterozoic

In the Mesoproterozoic Era, the Earth's continents continued to shift, and new geological features formed. This era also saw the development of more complex life forms.

Neoproterozoic Era

Main article: Neoproterozoic

The Neoproterozoic Era included dramatic climate changes, such as periods of extreme cold known as "Snowball Earth" events. Despite these challenges, life evolved, leading to the first complex animals and significant changes in Earth's ecosystems.

Phanerozoic Eon

Main article: Phanerozoic

The Phanerozoic Eon is a time period in Earth's history that began about 538.8 million years ago and continues to the present. It is known for the emergence of complex life forms, including many animals and plants that we are familiar with today.

During this time, several eras and periods mark significant changes in life on Earth. The Paleozoic Era saw the explosion of diverse sea creatures and the first animals on land. The Mesozoic Era is famous for the age of dinosaurs, which dominated the land, sea, and skies. Finally, the Cenozoic Era is known as the age of mammals, including the rise of primates and eventually humans. Each period brought new species and dramatic shifts in Earth's ecosystems, shaping the world we live in today.

Etymology of period names

The names of Earth's geological periods come from places where scientists first studied the rocks from those times. For example, the Jurassic period got its name from the Jura Mountains in France, where similar rocks were found. These names help us remember and organize the long history of our planet.

Visual summary

The image shows the history of nature from the Big Bang to today, with important events marked along a spiral. Each full turn of the spiral represents one billion years. The most recent 500 million years are shown in greater detail to highlight recent changes.