The earth is 4.5 billion years old

The Earth is approximately 4.54 billion years old. This isn't just a guess or a rough estimate. It is a precise age that scientists have confirmed using many different methods. When you measure the age of meteorites, moon rocks, and the oldest crystals found on Earth, all of the results point to the exact same staggeringly old age. Understanding how scientists figure out the age of the Earth is key to understanding how life had enough time to evolve.^{1, 2, 3}

How we date rocks

The main way scientists figure out how old a rock is involves something called radiometric dating. Early in the 1900s, scientists discovered that certain elements are naturally radioactive.⁵ This means they are unstable and will slowly break down (or "decay") into other, stable elements.

The amazing thing about radioactive decay is that it happens at an extremely predictable rate—like a clock ticking down. It doesn't matter if the rock has been buried deep underground, heated up, cooled down, or compressed. The radioactive "clock" keeps ticking at the exact same speed.^{6, 7}

One of the most common methods uses uranium. Over billions of years, uranium slowly decays into lead. Because scientists know exactly how long this process takes, they can look at an old crystal, measure how much uranium is left compared to how much lead has formed, and calculate almost exactly when that crystal originally formed.^{6, 8}

It's important to note that scientists don't rely on just one radioactive clock. They test the uranium-to-lead clock. Then they test the potassium-to-argon clock. Because each of these elements decays at a totally different speed, scientists can use them to double-check their work. When all of these different natural clocks in the same rock give the exact same age, scientists know the measurement is correct.^{6, 7}

(Note: You might have heard of "carbon dating" spreading in popular culture. Carbon dating is heavily used by archaeologists to date organic things like old wood, bones, or clothes. It is only useful for things younger than around 50,000 years old. It is not used to date rocks or determine the age of the Earth.^{9, 10})

Finding the oldest things in the solar system

The very first accurate measurement of the Earth's age was published in 1956 when a scientist named Clair Cameron Patterson used uranium-lead dating on a meteorite. He calculated the Earth was roughly 4.55 billion years old.¹ This number has been tested constantly over the last seventy years, and it has consistently held true. In 1995, advanced technology confirmed the age is 4.54 billion years old.²

Because the Earth is an active planet with volcanoes and shifting tectonic plates, the surface is constantly recycling itself, melting old rocks into new ones. This means finding original rocks from the very birth of the planet is incredibly rare. To find the true age of the solar system, scientists also look at objects in space.

Meteorites that fall from space are basically leftover building blocks from the creation of the solar system that never formed into planets. By dating these ancient space rocks, scientists have found that the oldest minerals in the solar system formed exactly 4.568 billion years ago.^{11, 12} Adding to that, the Apollo astronauts brought back rocks from the Moon that give dates between 3.1 and 4.4 billion years old.¹³

Down on Earth, the absolute oldest pieces of crust ever found are tiny crystals called zircons from Western Australia. Using highly advanced atom-mapping technology, scientists confirmed these tiny crystals are 4.374 billion years old.^{14, 15} The fact that Earth rocks, Moon rocks, and space rocks all point to an origin roughly 4.5 billion years ago is overwhelming proof of deep time.

Independent evidence for the age of the solar system^{1, 12, 14}

Reading the ice and trees

For more recent history, scientists don't even need radioactive dating. They can literally count the years, exactly like counting the rings inside a tree trunk.

In places like Antarctica and Greenland, snow falls every single year and gets packed into thick ice layers. Scientists can drill deep into this ice and pull out long "ice cores." Because summer snow and winter snow look chemically different, scientists can count the individual layers of snow, one by one, going back hundreds of thousands of years. The deepest ice core ever pulled from Antarctica holds a continuous, unbroken record of Earth's climate going back 800,000 years.⁴

For even more precise recent history, scientists look at trees. The oldest living trees on Earth, the bristlecone pines, can live for 5,000 years. By matching the patterns of thick and thin tree rings from living trees with long-dead fossilized wood, scientists have created an unbroken chain of counted tree rings spanning over 12,000 years into the past.¹⁷ There are also lakes in Japan and Europe where mud settles at the bottom in perfect annual layers. One lake in Japan has 50,000 uninterrupted layers of mud, each marking a single year.¹⁰

Counting deep time without radioactive dating^{4, 9, 10, 17}

Enough time for evolution

4.54 billion years is a nearly incomprehensible amount of time.

To put this in perspective, imagine all of Earth's history squeezed down into a single 24-hour day. The first tiny microscopic life forms appear in the oceans before dawn. The first tiny crawling sea animals don't show up until around 9:00 PM. The dinosaurs rule the Earth for just an hour, getting wiped out by an asteroid at 11:39 PM. Every single human being who has ever lived—from the cavemen to modern-day astronauts—exists in the very last minute before midnight.^{3, 16}

Some people say evolution is impossible because there wasn't "enough time." But that completely misunderstands how fast evolution actually works. When scientists grow bacteria in the lab, they can watch the bacteria evolve totally new survival skills in just a few decades.¹⁸ When you stretch that process out over billions of years, there is an incredibly vast amount of time for natural selection and genetic mutations to transform the earliest, simple lifeforms into every single plant, animal, and human swimming, running, or flying on the Earth today.¹⁸