Climate History Explained: From Ice Ages to Today

0:04For billions of years on Earth, changes in climate have meant changes for life. Earth's climate affects where, how, and whether life can exist on Earth, sometimes in dramatic ways. The history of life on Earth is a story of how life has been altered by changes in climate. Today, another period of climate change is causing big changes. And we can look to history to understand how it might affect our future and whether it will usher in the next big change for humanity.

0:40The first climate-driven change in Earth's history began around 4 billion years ago. Earth was really hot, and its atmosphere was full of water vapor and gases but very little oxygen. Over time, Earth cooled down and water vapor collected, forming oceans. These young oceans are where life likely began. The earliest life was anaerobic. It didn't use oxygen to survive.

1:09But after about 2 billion years, tiny microbes called cyanobacteria evolved and they began to release a lot of oxygen into the atmosphere. All this new oxygen caused big changes on Earth. It actually poisoned and killed off a lot of anaerobic life in an event that's sometimes called the Oxygen Holocaust. But it also paved the way for more complex organisms that required oxygen to live. And it helped form Earth's atmosphere as we know it today. Oxygen began to replace most of the methane in the atmosphere. And since methane traps the sun's heat to warm Earth, replacing it with oxygen cooled things way down, ice sheets began to form across Earth. Since then, Earth has gone through several more periods of warming and cooling that changed landscapes, the

2:08atmosphere, and life. Like around 6 million years ago, Earth became warmer and drier, and the grassy African savannah expanded, creating more open spaces. Some researchers think this is what led early ancestors of humans to leave trees and begin walking on two legs, which also led to more brain development. Humans began to develop new tools and technology, share stories and information, and plan ahead. This new ability to communicate and share information, which we call collective learning, allowed them to survive through an ice age between 21,000 and 24,000 years ago.

2:49Then between 5,000 and 9,000 years ago, a period sometimes called the Holocene Climate Optimum, created ideal conditions for planting crops. This led to one of the most important innovations in human history, agriculture. Farming spread to new places and helped develop new complex societies.

3:11Climate also continued to affect these complex societies. Warmer temperatures and drought may have caused widespread famine and led to the collapse of the Bronze Age around 1,200 BCE and the decline of the Great Mayan city-states around 900 CE. And cooler temperatures in the northern hemisphere from the 1300s to the 1800s caused a period called the Little Ice Age. During this time, periods of unusual cold and drought caused widespread crop failures and famines.

3:44Some historians argue that the Little Ice Age helped spark revolutions and bring about the birth of the modern world. And that modern world is experiencing climate change again. Only this time, it's not happening naturally. Instead, it's caused by human activities. Around 300 years ago, human societies found new energy sources called fossil fuels, beginning the modern revolution. Our societies today still run on energy created by burning fossil fuels, which light our homes, power our cars and computers, and keep us fed. But every time we use them, they release greenhouse gases that sit in the atmosphere, and trap heat from the sun, warming the planet. This warming means we're facing devastating hurricanes, wildfires,

4:38droughts, and floods. At the same time, many companies and countries are looking for ways to reduce greenhouse gas emissions. They're turning towards renewable energy sources like wind and solar power that don't warm the planet. People are figuring out how to use liquid hydrogen, which can already power things like vehicles, to generate and store electricity. And they're experimenting with fusion energy, which involves combining atoms to release energy. People are also working on solutions for adapting to climate change, like building homes and cities to withstand floods and extreme weather, or growing drought resistant crops. And we have hundreds of millions of years of climate history to look back on to show us the effects climate change can have

5:28and how we can respond. Will this knowledge and innovation produce an energy bonanza for humanity, propelling our societies to new heights of complexity? Or could the threat of climate change prove too much for us to solve, slowing down the progress of the modern revolution?