How Old Is The Earth And How Did Scientists Figure It Out?

It doesn’t take a genius to understand that the Earth is really old. But just how old is it, and how do scientists know?

Creationists like Ken Ham would have us believe that our planet is only 6,000 years old and that humans rode dinosaurs and that all of history is compressed into just that narrow time-frame.

Ham and others like him make these claims without any scientific evidence.

Scientists, however, have a multitude of evidence proving that Earth is not only older than 6,000 years, it’s approximately 4.5 billion years old. And the majority of scientists accept that consensus.

First, let’s easily debunk the claim that Earth is 6,000 years old.

In Spain, researchers discovered the world’s oldest human feces that were deposited by Neanderthals 50,000 years ago. We know this because of the chemical composition and the fact that the scat was found in a layer of rock that is 50,000 years old.

That’s a right, a piece of sh*t literally debunks creationists’ claim that Earth is only 6,000 years old.

But Earth is even older than that, and rocks and rock layers, just like the one the poop was found in, are the reason why we know it.

According to

The oldest rocks on Earth found to date are the Acasta Gneisses in northwestern Canada near the Great Slave Lake, which are 4.03 billion years old. Rocks older than 3.5 billion years can be found on all continents. Greenland boasts the Isua Supracrustal rocks (3.7 to 3.8 billion years old), while rocks in Swaziland are 3.4 to 3.5 billion years. Samples in Western Australia run 3.4 to 3.6 billion years old.

Research groups in Australia found the oldest mineral grains on Earth. These tiny zirconium silicate crystals have ages that reach 4.3 billion years, making them the oldest materials found on Earth so far. Their source rocks have not yet been found.

These minerals, known as zircons, are dated through a process called radioisotopic dating, which involves the use of a mass spectrometer.

The University of California at Berkeley described radioisotopic dating as the “key tool for studying the timing of both Earth’s and life’s history.”

This suite of techniques allows scientists to figure out the dates that ancient rock strata were laid down — and hence, provides information about geologic processes, as well as evolutionary processes that acted upon the organisms preserved as fossils in interleaved strata.

To put it simply, scientists measure the amount of radioactive decay within the zircons, which usually contain lead that was formerly uranium. The half-life of uranium is 704 million years.

As UC-Berkeley explains:

That means that in 704 million years, one gram of uranium will be reduced to ½ gram of uranium. And in the next 704 million years, it will decay leaving behind ¼ gram, and in the next 704 million years, it will decay leaving behind ⅛ gram and so on. At the same time, the amount of the element that it decays into (in this case lead-207), will increase accordingly…

Now, creationists often confuse radioisotopic dating with radiocarbon dating, usually claiming that carbon dating is proof that scientists are lying about the age of Earth because that particular technique can only measure dates to up to 50,000 years old.

Still, that disproves the ole “Earth is 6,000 years old” claim, but only radioisotopic dating can accurately measure the age of a rock, and thus, the Earth.

Scientists and non-scientists alike have been observing that Earth is billions of years old for centuries, beginning with Nicolas Steno in the 1660s, who laid the foundation for the study of rock layers, or strata.

University of Glasgow chemistry professor Paul Braterman writes that “[i]t was not until 1926, when the National Academy of Sciences adopted the radiometric timescale, that we can regard the controversy as finally resolved. Critical to this resolution were improved methods of dating, which incorporated advances in mass spectrometry, sampling and laser heating. The resulting knowledge has led to the current understanding that the earth is 4.55 billion years old.”

But the oldest zircons are only 4.3 billion years old, which, while enough to disprove creationists like Hamm, still falls short of the estimated age of Earth.

However, it’s not just rocks on Earth that scientists study. As Washington Post science reporter Sarah Kaplan points out, “even the oldest zircons are not as old as the Earth itself. Everything on our world eventually is eroded or subsumed back into the crust. To get a truly precise date for the origin of our planet, scientists have to look beyond it.”

And so, scientists have been using radioiotopic dating to figure out the age of rocks and minerals found in meteorites, moon rocks and asteroids.

When scientists used the technique on fragments of the Canyon Diablo meteorite that crashed into our planet 50,000 years ago, the age was determined to be about 4.5 billion years, which is the most accurate age of Earth so far.

Why would scientists study meteorites to determine the age of Earth?

Well, our planet is a giant recycler that is constantly taking old rocks and melting them down and creating new rocks. This recycling, however, is not done by meteorites. They are hunks of rock and metal that have been floating through our solar system since the beginning of the universe.

Speaking of the universe, scientists can also estimate how old it is, too.

According to the U.S. Geological Survey:

The age of the Universe can be estimated from the velocity and distance of galaxies as the universe expands. The estimates range from 7 to 20 billion years, depending on whether the expansion is constant or is slowing due to gravitational attraction. The age of the Galaxy is estimated to be 14-18 billion years from the rate of evolution of stars in globular clusters, which are thought to be the oldest stars in the Galaxy. The age of the elements in the Galaxy, based on the production ratios of osmium isotopes in supernovae and the change in that ratio over time due to radioactive decay, is 8.6-15.7 billion years.

The power of science is truly mind-blowing. It certainly makes the heads of creationists explode.

As these techniques are refined and better technology is developed, the Earth’s age could get even more accurate. For now, 4.5 billion years is the best answer scientists have for us.


Featured Image: Wikimedia

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