Posted on 02/09/2019 12:13:39 PM PST by ETL
Planet Earth doesn't have a birth certificate to record its formation, which means scientists spent hundreds of years struggling to determine the age of the planet. By dating the rocks in Earth's ever-changing crust, as well as the rocks in Earth's neighbors, such as the moon and visiting meteorites, scientists have calculated that Earth is 4.54 billion years old, with an error range of 50 million years.
Scientists have made several attempts to date the planet over the past 400 years. They've attempted to predict the age based on changing sea levels, the time it took for Earth or the sun to cool to present temperatures, and the salinity of the ocean. As the dating technology progressed, these methods proved unreliable; for instance, the rise and fall of the ocean was shown to be an ever-changing process rather than a gradually declining one.
And in another effort to calculate the age of the planet, scientists turned to the rocks that cover its surface. However, because plate tectonics constantly changes and revamps the crust, the first rocks have long since been recycled, melted down and reformed into new outcrops.
Scientists also must battle an issue called the Great Unconformity, which is where sedimentary layers of rock appear to be missing (at the Grand Canyon, for example, there's 1.2 billion years of rock that can't be found). There are multiple explanations for this uncomformity; in early 2019, one study suggested that a global ice age caused glaciers to grind into the rock, causing it to disintegrate. Plate tectonics then threw the crushed rock back into the interior of the Earth, removing the old evidence and turning it into new rock.
In the early 20th century, scientists refined the process of radiometric dating. Earlier research had shown that isotopes of some radioactive elements decay into other elements at a predictable rate. By examining the existing elements, scientists can calculate the initial quantity of a radioactive element, and thus how long it took for the elements to decay, allowing them to determine the age of the rock.
The oldest rocks on Earth found to date are the Acasta Gneiss in northwestern Canada near the Great Slave Lake, which are 4.03 billion years old. But 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 billion to 3.5 billion years. Samples in Western Australia run 3.4 billion 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.
The rocks and zircons set a lower limit on the age of Earth of 4.3 billion years, because the planet itself must be older than anything that lies on its surface.
When life arose is still under debate, especially because some early fossils can appear as natural rock forms. Some of the earliest forms of life have been found in Western Australia, as announced in a 2018 study; the researchers found tiny filaments in 3.4-billion-year-old rocks that could be fossils. Other studies suggest that life originated even earlier. Hematite tubes in volcanic rock in Quebec could have included microbes between 3.77 and 4.29 billion years ago. Researchers looking at rocks in southwestern Greenland also saw cone-like structures that could have surrounded microbial colonies some 3.7 billion years ago.
Meet the neighbors
In an effort to further refine the age of Earth, scientists began to look outward. The material that formed the solar system was a cloud of dust and gas that surrounded the young sun. Gravitational interactions coalesced this material into the planets and moons at about the same time. By studying other bodies in the solar system, scientists are able to find out more about the early history of the planet.
The nearest body to Earth, the moon, doesn't experience the resurfacing processes that occur across Earth's landscape. As such, rocks from early lunar history still sit on the surface of the moon. Samples returned from the Apollo and Luna missions revealed ages between 4.4 billion and 4.5 billion years, helping to constrain the age of Earth. How the moon formed is a matter of debate; while the dominant theory suggests a Mars-size object crashed into Earth and the fragments eventually coalesced into the moon, other theories suggest that the moon formed before Earth.
In addition to the large bodies of the solar system, scientists have studied smaller rocky visitors that have fallen to Earth. Meteorites spring from a variety of sources. Some are cast off from other planets after violent collisions, while others are leftover chunks from the early solar system that never grew large enough to form a cohesive body.
Although no rocks have been deliberately returned from Mars, samples exist in the form of meteorites that fell to Earth long ago, allowing scientists to make approximations about the age of rocks on the Red Planet. Some of these samples have been dated to 4.5 billion years old, supporting other calculations of the date of early planetary formation.
More than 70 meteorites that have fallen to Earth have had their ages calculated by radiometric dating. The oldest of these are between 4.4 billion and 4.5 billion years old.
Fifty thousand years ago, a rock hurled down from space to form Meteor Crater in Arizona. Shards of that asteroid have been collected from the crater rim and named for the nearby Canyon Diablo. The Canyon Diablo meteorite is important because it represents a class of meteorites with components that allow for more precise dating.
In 1953, Clair Cameron Patterson, a renowned geochemist at the California Institute of Technology, measured ratios of lead isotopes in samples of the meteorite that put tight constraints on Earth's age. Samples of the meteorite show a spread from 4.53 billion to 4.58 billion years. Scientists interpret this range as the time it took for the solar system to evolve, a gradual event that took place over approximately 50 million years.
By using not only the rocks on Earth but also information gathered about the system that surrounds it, scientists have been able to place Earth's age at approximately 4.54 billion years. For comparison, the Milky Way galaxy that contains the solar system is approximately 13.2 billion years old, while the universe itself has been dated to 13.8 billion years.
Further reading:
This article was updated on Feb. 7, 2019, by Space.com contributor Elizabeth Howell.
Yes, you can find someone on FR to defend any notion that’s out there. As long as I’ve been here, it still surprises me the number of screen names I see for the first time every day.
How old is the Earth? How uncouth! A gentleman doesn’t ask.
How old is the Earth? How uncouth! A gentleman doesn’t ask.
Great comment. Maybe God’s time is different than our time. Maybe He invented time as a reference for us. Maybe since He had no beginning or ending, time was irrelevant. Maybe the only real definition of time is observed as 9.2 billion vibrations of a cesium atom, because we don’t really have a good handle of what time is. Time is relevant only to the space that we currently occupy. Just theories, but your comment is an excellent point. If it was created for our use, then does it really apply to other planes of existence?
And while we are at that notion. I have a concern that there may be some here who are just here to make everyone here look foolish as “Republicans and Conservatives”. Sometimes I ask myself if there are really so many on our side so ignorant as to make us all look so ignorant, inept, and racist. It sure doesn’t do us any good or support our true nature and position. If not suspect, then we have earned every damned thing they accuse us of without a doubt.
From my observations there needs to be a little extra scrutiny in this department.
Yes, I always thought it was the crust moving over a fixed hot spot, but I suppose it is also possible that the inner Earth is rotating at a slightly different rate than the crust, hence a moving hot spot relative to the crust. In fact, it probably makes more sense that the gooey mantle is sliding/spinning even more slowly than the more liquid core.
“Time is relevant only to the space that we currently occupy.”
From what I now understand this a very astute and relevant possibility.
Wouldn’t it be a hoot to finally perfect inter-galactic travel only to find out half the other galaxies are made of anti-matter. It could happen!
Absolutely makes sense. We keep looking at everything in 2D when in reality there may be more axis of movement we don’t understand and it should actually be viewed as 3D.
I had a structural geology professor in the mid 1970s who was opposed to plate tectonics from his viewpoint all orogenic activity, i.e. mountain building could be explained by geosynclines. Being a geophysics major was a “rough course” for me!
Wow. He must have been tenured.
How else could you teach personal
hogwash and stay employed?
One thing I learned a long time ago, and I hope I am not the only one, but I never discredit any theory. Far too many times I judged these as false and they turned out to be true. Nope... I am not going to be ignorant and throw up a mental firewall, I will always have an open mind. Doesn’t mean I have to follow them off the cliff though. :)
I have a curious and respectful question. Do you remember what the current acceptable 100 year “sink rate” is? Only asking because I would like to make a historical building comparison that might baffle some.
Add to that the random variable of comet/asteroid strikes imparting enough force to upset the boundaries of these spheres of varied speed, one within the other, and creating internal tsunamis of magma and liquid nickel and now you've got your hot spots welling up on the opposite side of the disturbance.
It's a theory. I'm sure someone much smarter than me has already thought of it.
You could probably form an experimental model on the ISS with a rotating ball of hot soup with tiny sensors suspended within. Start cooling it and then shoot it with a bb and observe. I'm not a scientist, but that's how I'd go about testing it.
And old! Looking back I was an idiot for fighting with him. I got a bad grade in structural which made both going further like grad school in the geosciences or a job harder to do. The good thing for me (Though my parents were very annoyed with it at the time!) I had enough physics hours if I took one more year I would get a dual degree. That’s what annoyed dear old mom & dad! Me being stubborn again & costing them extra money! I was kind of known for that in those days! I did make up for it later. What did I do, grad school and/or job-wise, worked 6 months then went grad school in electrical engineering! That almost gave my father apoplexy! Another zigzag by me that took a lot of explaining! It helped this time he didn’t have to contribute any money!
No I don’t remember that!
If you can give me some context I will dig around.
I think you are on the right track. Our crust is no more thick as an eggshell on an egg. And it is fractured everywhere. We are standing on precarious soil...
The reality is actually a bit intimidating. lol
Structural geological engineering teaches safe places to build, this is especially important for huge buildings such as high-rises. If I remember right the current accepted “sink rate” specification is no more than 6 inches in a hundred years. Here’s one though... The ancient pyramids have not sunk more than a half inch since they were built. Since you studied this I had to bring it up as an interesting odd factoid. :)
Isn’t that incredible? Apparently they had some sort of knowledge about this science. :)
Somebody wake up Ruth Bader Ginsburg and ask her how old the earth is. She was there at its’ birth.
She was the “Ruth” in the old Testament when she was a teenager.
That is why one of the first chocolate candy bars made millennia ago was named “Baby Ruth” in her honor. Besides it has a lot of her characteristics, nuts.
#1. Nice picture of Gneiss and people think it is the oldest rock type known to man. No Schist!
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