Will Earth Last Forever?

Everything that has a beginning has an end. Like Earth. It will last for a very long time, and its end will come billions of years after anyone who is alive here now is gone.

Before we talk about the future of our planet, let's review its history and when life appeared on it. The history of human beings is very, very short compared with that of Earth.

Earth Is at Least 4 Billion Years Old

Our planet formed from a giant cloud of gas and dust in space, which is called a nebula, about 4.6 billion years ago. The first continent might have formed on its surface as early as 4.4 billion years ago.

The atmosphere of early Earth did not contain oxygen, so it would have been toxic to human beings if they had been present then. It was very different from Earth's atmosphere today, which is about 21 percent oxygen. Many life forms, including humans, need oxygen to live.

Where did that oxygen come from? Scientists believe that atmospheric oxygen started to rise about 2.4 billion years ago in a shift they call the Great Oxidation Event.

Tiny microorganisms had already existed on Earth's surface for a while. Some of them developed the ability to produce energy from sunlight, the way plants do today. As they did it, they released oxygen. It built up in the atmosphere and made it possible for more complex life forms to evolve.

This took a long time. The first animals, which may have been sea sponges, probably appeared about 660 million years ago. Depending how we define humans, humans emerged in Africa between about 200,000 years and 2 million years ago and spread out everywhere from there.

Earth Will Be Here for Billions More

Now, as we think about the future of Earth, we know there are two essential factors that humans need to live here.

First, the sun provides most of the energy that living things on Earth need to survive. Plants use sunlight to grow and to produce oxygen. Animals — including humans — rely directly or indirectly on plants for food and oxygen.

The other thing that makes Earth habitable for life is that our planet's surface keeps moving and shifting. This ever-changing surface environment produces weather patterns and chemical changes in the oceans and on the continents that have enabled life to evolve on Earth.

The movement of the giant pieces of Earth's outer layer, which are called tectonic plates, is driven by heat in the interior of Earth. This heat source will keep Earth's interior hot for billions of years.

So, what will change? Scientists estimate that the sun will keep shining for another 5 billion years. But it will gradually get brighter and brighter, and warm Earth more and more.

This warming is so slow that we wouldn't notice it. In about 1 billion years, our planet will be too hot to maintain oceans on its surface to support life. Given that the average human life span is about 73 years that's about 13 million human lifetimes.

Long after that — about 5 billion years from now — our sun will expand into an even bigger star that astronomers call a "red giant," which eventually will engulf Earth. Just as our planet existed for more than 4 billion years before humans appeared, it will last for another 4 billion to 5 billion years, long after it becomes uninhabitable for humans.

Shichun Huang is an associate professor of Earth and planetary sciences at the University of Tennessee.

This article is republished from The Conversation under a Creative Commons license. You can find the original article here.