The Earth was formed 4.6 billion years ago from the solar nebula, a rotating disk of gas and dust that surrounded the Sun. The Moon was formed when a Mars-sized object collided with Earth and the debris ejected into space formed the Moon. Early Earth’s atmosphere was composed of gases such as nitrogen, carbon dioxide, and methane but evolved over time due to volcanic eruptions and the evolution of photosynthetic organisms. The first continental crust appeared 4 billion years ago, and continents continued to drift, collide and separate into the present-day continents. The Cenozoic Era began 66 million years ago, known as the Age of Mammals, and is marked by a cooling of the Earth’s climate and the evolution of humans.
From the Beginning of Time: A Timeline of Geologic Events
The Formation of Earth
The history of Earth can be traced back 4.6 billion years ago when it was formed from the solar nebula. The solar nebula was a rotating disk of gas and dust that surrounded the Sun when it was young. The gravitational pull of the disk caused the particles to come together to form planets.
The Formation of the Moon
About 4.5 billion years ago, a Mars-sized object collided with Earth. This impact caused debris to be ejected into space that eventually formed the Moon. The moon has been orbiting around Earth ever since.
The Formation of the Atmosphere
Early Earth’s atmosphere was composed of gases such as nitrogen, carbon dioxide, and methane. However, volcanic eruptions released new gases such as water vapor, carbon monoxide, and sulfur dioxide. Over time, photosynthetic organisms evolved, producing oxygen and removing carbon dioxide, which altered the composition of the atmosphere greatly.
The Formation of Continents
4 billion years ago, the first continental crust appeared. Continents form when tectonic plates move apart, allowing magma to rise and cool, forming new crust. These continents continued to drift, collide and separate into the present-day continents.
The Ice Age
The first ice age was around 2.6 billion years ago. This led to the formation of glaciers that covered much of the Earth’s surface. As the Earth warmed over time, glaciers retreated, leaving behind evidence of their presence, such as U-shaped valleys and moraines.
The Age of Dinosaurs
During the Mesozoic Era — between about 252 and 66 million years ago — dinosaurs roamed the Earth. This era was marked by a warmer global climate and widespread volcanic activity. The continents were separate, with some members missing altogether.
The Age of Mammals
The Cenozoic Era began about 66 million years ago and continues today. It is known as the Age of Mammals, as mammals came to dominate life on Earth. This era was marked by a cooling of the Earth’s climate, the formation of the Himalayas and other mountain ranges, and the evolution of humans.
Frequently Asked Questions
Q: How old is the Earth?
A: The Earth is approximately 4.6 billion years old.
Q: How was the Moon formed?
A: The Moon was formed around 4.5 billion years ago when a Mars-sized object collided with Earth and ejected debris into space that eventually formed the Moon.
Q: What caused the Ice Age?
A: The Ice Age was caused by a combination of factors, including changes in the Earth’s orbit, atmospheric composition, and continental drift.
Q: What was the Age of Dinosaurs?
A: The Age of Dinosaurs was during the Mesozoic Era between 252 and 66 million years ago. During this time, dinosaurs were the dominant species on Earth.
Q: What is the Cenozoic Era?
A: The Cenozoic Era began about 66 million years ago and is known as the Age of Mammals, as mammals came to dominate life on Earth.