How old is the Earth? 4.54 billion years, and how scientists know

The Earth is about 4.54 billion years old. That is the US Geological Survey's "best age for the Earth (4.54 Ga)", where Ga means billion years. Scientists estimated it by comparing different forms of lead in meteorites and in Earth materials, using the decay of uranium into lead as a clock. Some key ages:

How old is the Earth?

About 4.54 billion years, or 4,540 million years. You will also see "4.5 billion" or "4.6 billion": those are rounded numbers, or the age of the whole solar system, which NASA says "formed about 4.6 billion years ago". The International Commission on Stratigraphy (ICS), which keeps the official geologic time scale, starts its oldest eon (an eon is one of the largest divisions of geological time), the Hadean, at 4,567 million years ago, when the solar system began.

That makes the Earth roughly a third as old as the universe (13.8 billion years). The number has held up well: in 1956 the geochemist Clair Patterson calculated "4·55 ± 0·07 × 10^9 yr" (4.55 billion years, give or take 70 million), close to today's 4.54 billion.

Rock layers, like those in the Grand Canyon, record a lot of Earth's history, but they are far younger than the Earth itself. So how do scientists measure billions of years?

How do scientists know? Radioactive clocks in rocks

Isotopes are versions of the same element. Some are unstable and change into other elements over time; the USGS calls the original isotope the "parent" and the new one the "daughter". The speed is given by the half-life: the time in which half of the original radioactive atoms are expected to change.

When a crystal forms, it locks in some uranium. From then on, the uranium slowly turns into lead (through a chain of shorter-lived steps), and the new lead stays inside. Measure how much of that lead there is for each uranium atom, and you can work out how long the clock has been ticking. This simple clock assumes that no uranium or lead has entered or escaped since the crystal formed; scientists also correct for any lead that was already there at the start. After 4.54 billion years, about 50% of the uranium-238 is left, and there is about 1.01 atom of lead-206 for every atom of uranium-238 (our calculation with the USGS half-life; the animation below shows this idealised clock). The faster uranium-235 clock gives a second, independent check: only about 1.1% of it is left after the same time.

Carbon dating cannot do this job: the USGS says carbon-14 "can be used for dating events that have taken place only within the past 50,000 years".

Why the Earth's age comes from meteorites

You might expect scientists to simply date the oldest rock on Earth. But the USGS explains that they "have not found a way to determine the exact age of the Earth directly from Earth rocks because Earth's oldest rocks have been recycled and destroyed by the process of plate tectonics". The ground under our feet keeps being pushed down, melted and made again.

Meteorites are pieces of the early solar system that were not recycled in this way. In 1956 Clair Patterson measured lead in several meteorites and found that, within experimental error, three independent radioactive methods gave the meteorites one and the same age. Using comparisons between meteorite lead and lead from Earth, and with stated assumptions, he argued that Earth's lead fits the same pattern, and wrote: "It is therefore believed that the age for the earth is the same as for meteorites." One key sample came from the Canyon Diablo iron meteorite, the meteorite that formed Meteor Crater in Arizona (photo above), according to the Linda Hall Library. Patterson took its lead from a mineral (troilite) with almost no uranium, so it still showed what lead looked like when the meteorites formed: a starting point for the clock. The USGS still bases its best age on lead from "iron meteorites, specifically the Canyon Diablo meteorite", and gives "an age for the Earth and meteorites, and hence the Solar System, of 4.54 billion years with an uncertainty of less than 1 percent".

The oldest rocks and crystals on Earth

Earth rocks cannot give the exact age, but they set a minimum. The USGS lists the Acasta Gneisses in northwestern Canada at about 4.03 billion years. In 2025 a study in the journal Science, led from the University of Ottawa, reported even older rocks, about 4.16 billion years old, in the Nuvvuagittuq Greenstone Belt in northern Quebec. Older still are tiny zircon crystals from Western Australia, such as those from the Jack Hills (photo above): the USGS reports zircons with ages of 4.4 billion years. The crystals survived even though the rocks they first grew in did not.

Such finds show how old the Earth must at least be, but, in the USGS's words, they "do not reveal the exact age of Earth's formation". That is why meteorites are needed for the full answer.

Earth's history in one day

Billions of years are hard to imagine, so we squeezed Earth's 4.54 billion years into one day: Earth forms at midnight and "now" is the next midnight. On that clock, one second stands for about 52,546 years.

The clock times are our calculation; the Moon's date is approximate. For most of the day, the known fossils are of microscopic life. The Cambrian period begins at about 21:09, and animal groups diversified during the "Cambrian explosion" over millions of years around that part of the timeline. The non-bird dinosaurs die out about 21 minutes before midnight (birds are surviving dinosaurs, the National Park Service notes). The four colours in the animation are the four eons of the ICS time scale: Hadean, Archean, Proterozoic and Phanerozoic. See also is there life on other planets, where we use Earth as a yardstick.

Is the Moon older than the Earth? The Sun? The universe?

• The Sun and the solar system are a little older than the Earth: NASA says the solar system "formed about 4.6 billion years ago from a dense cloud of interstellar gas and dust".
• The Moon is a little younger. NASA explains that something about the size of Mars probably crashed into the young Earth "about 4.5 billion years ago", flinging out debris that became the Moon. Dating the Moon rocks brought back by the Apollo astronauts showed "that the Moon formed around 60 million years after the solar system began to form". The Apollo 8 photo above shows the Earth rising over the Moon. See how far the Moon is from Earth.
• The universe is much older: about 13.8 billion years, roughly three times the age of the Earth.

How long have humans been on Earth?

Our species, Homo sapiens, has existed for about 300,000 years; earlier human ancestors lived millions of years before us. According to the Smithsonian's Human Origins Program, the traits shared by all people "evolved over a period of approximately six million years", walking on two legs "evolved over 4 million years ago", and early humans first left Africa for Asia "probably between 2 million and 1.8 million years ago". Homo sapiens "evolved in Africa" about 300,000 years ago.

Compared with Earth's age, that is about 0.0066% of its history for Homo sapiens, and about 0.132% for the six-million-year span of early human ancestors (our calculation). On the one-day clock, Homo sapiens appears about 6 seconds before midnight.

Age of the Earth FAQ

How old is the Earth in years? About 4.54 billion years, or 4,540,000,000 years (USGS). Patterson's 1956 measurement gave 4.55 billion, plus or minus 70 million.

How certain are scientists about Earth's age? Not to the exact year. The USGS gives about 4.54 billion years, with an uncertainty of less than 1%. Patterson's 1956 estimate was 4.55 billion years, plus or minus 70 million.

How do we know Earth is 4.5 billion years old? By comparing different forms of lead in meteorites that formed with the Earth, using uranium's decay into lead as a clock, and checking that lead from Earth fits the same pattern (Patterson, 1956; USGS).

What are the four ages of the Earth? The four eons of the official time scale (ICS): the Hadean, the Archean (from 4,031 million years ago), the Proterozoic (from 2,500 million years ago) and the Phanerozoic (from 538.8 million years ago), which we live in.

What is the oldest part of the Earth? Tiny zircon crystals from Western Australia, about 4.4 billion years old (USGS). The oldest known rocks, reported in 2025, are about 4.16 billion years old, in the Nuvvuagittuq Greenstone Belt in Quebec; the Acasta Gneiss in Canada is about 4.03 billion years old.

How old was the Earth before Homo sapiens appeared? About 4.54 billion years minus 300,000 years: practically its whole age. Homo sapiens has been here for about 0.0066% of Earth's history.

When did life begin on Earth? The oldest confirmed fossils are about 3.5 billion years old (NASA), so life was there within about a billion years of Earth forming, maybe earlier.

Can carbon dating tell the age of the Earth? No. Carbon-14 has a half-life of 5,730 years and only works for the past 50,000 years or so (USGS). Uranium-lead clocks are used for billions of years.

What does the Bible say about the age of the Earth? The Bible does not state the Earth's age as a number; people have calculated dates from it. In 1650 Archbishop James Ussher used the genealogies in the Old Testament to arrive at a creation date of 4004 BC, about 6,000 years ago, and from 1701 that date was printed in the margins of King James Bibles, according to the Linda Hall Library. Scientists measure the Earth's age with radioactive clocks instead: about 4.54 billion years.

How we checked

Our main evidence is the USGS (Earth's age and its uncertainty, oldest rocks and crystals, half-lives), Patterson's 1956 paper, the ICS geologic time scale (version 2024/12), NASA and the 2025 Science study on the Nuvvuagittuq rocks; the full list is under Sources. We checked all sources on 20 October 2026.

The one-day clock, the uranium percentages and the shares of Earth's history are our calculations (86,400 seconds for 4.54 billion years; the decay law with the USGS half-lives). The Moon's date is approximate, and the uranium animation is an idealised model. None of the images or videos is AI-generated.