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.
“We measure time, I think, by segments of our choosing.”
Einstein showed that time is not constant, it is relative, and affected by among other things, gravity,.
If you travel at the speed of light for 40 years and then return to earth, you will find that earth will have aged 100,000 years, not 40 years.
So how much time passed in that period?
It was here when I was born so it’s oooooooold.
Why the sharp right turn?
Good question, I’m not sure... Something from the past? an event? Maybe the plate changes stress directions as it moves north? I haven’t nailed that question down yet with a viable theory so I can’t claim anything with this very good question yet. :)
But the age difference between each island and mount is about 200,000 years in sequence from the southern newest still active to the northern oldest respectively. And they claim a new one is starting to pop just east of the “big island” any time now.
It’s quite a phenomenon that is pretty hard to dispute when discussing the age of the earth. If you believe it’s any younger you are still in the dark ages. The geology with this is pretty simple and self explanatory.
I understand. I took three college level geology courses and I find this stuff fascinating.
See the “V” it heads into just before it slides under between the Russian Peninsula and the Aleutian plates? I think that might be an indicator that the chain is caught in the middle between two different plate pushes both northeast and northwest as they move towards that V.
I find it fascinating too... Had two very successful great uncles who were geologists extraordinaire. I was fortunate to have had apprentice time with them before they passed and learned quite a bit.
https://geology.com/usgs/hawaiian-hot-spot/
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The Hawaiian-Emperor Chain
Over a span of about 70 million years, the combined processes of magma formation, eruption, and continuous movement of the Pacific Plate over the stationary hot spot have left the trail of volcanoes across the ocean floor that we now call the Hawaiian-Emperor Chain. A sharp bend in the chain about 2,200 miles northwest of the Island of Hawai’i was previously interpreted as a major change in the direction of plate motion around 43-45 million years ago (Ma), as suggested by the ages of the volcanoes bracketing the bend.
However, recent studies suggest that the northern segment (Emperor Chain) formed as the hot spot moved southward until about 45 Ma, when it became fixed. Thereafter, northwesterly plate movement prevailed, resulting in the formation of the Hawaiian Ridge “downstream” from the hotspot.
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Thank you! So I had it backwards. It was the hot spot that moved at some point. Good find, I learned from it!
What made it move??? What changed this??? Always leads to a question... lol
Don’t know but there is probably multiple PHDs on the government payroll, who couldn’t find gainful employment elsewhere, researching it for the last 40 years.
I would bid on a private contract to do this for them for one tenth the cost. :)
“Does it really, really matter since we’re the ones that created ‘time’.”
Maybe everything happens instantly but our observations of those things are warped.
If Earth had, at one time, been only 51 million miles from the Sun, what would it be like now,4.5 billion years later?
Old.
The Hawaiian islands I think are less than 100 million years old, while the earth is estimated at 4,600 million.
That is very possible. Depends on the rate of plate slide which is a hard factor to actually figure. Which of course looks like it may have changed speed a few times by looking at it. It also looks like there may have been a lull in the storm with less tectonic activity in the whole of the timeline.
I personally think the whole slate has been wiped clean several times in the last 4.6 million years. And I think we are about ready for it to happen again. I think we are only getting half the real story of our geological history. A story that even the rocks do not remember because they have been recycled so many times.
Olivine is the key... find and age the Olivine.
I’m so old, I remember telling a fifth grade teacher that the continents looked like they could fit together, and she said it was just a coincidence. In those days, there were canals on Mars, too.
There are still canals on Mars to some... lol
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