१५ नोव्हेंबर, २०१९
"A lot of people study the last 2.5 billion years, but we will emphasize the first 2 billion. This is the earliest, most exciting era, mainly because there are no known rocks."
From "Professor’s study of ancient crystals sheds light on earth’s early years" (at news.wisc.edu)(about studying zircons with "melt inclusions").
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Geology is one of the most romantic of the sciences.
There is something wrong with this quote, the oldest known rocks are 4.28 billion years old. There are fossils that 3.5 billion years old.
"There is something wrong with this quote..."
I know. I was a bit confused. There's much talk of the zircons. Inside the zircons are other bits that can be studied... But are they not "known"?!
Maybe someone can explain.
So the Rolling Stones are not as old as they look?
There is something wrong with this quote,
A journalist was trying to understand something beyond their means - the article was a real mess.
Beloved Commenter AReasonableMan said...
There is something wrong with this quote, the oldest known rocks are 4.28 billion years old. There are fossils that 3.5 billion years old.
A journolist screw up the facts? Why, I never . . .
Everybody has experience it. You see an article in the paper about something you know about, and a journalist has mischaracterized the facts, and gotten something wrong.
Then you turn the page and read about something you don't know about, and assume the writer is correct. It even has a name, the Gell-Mann Amnesia Effect.
"Rock" can mean layer or strata, boulder, pebble, or tiny crystal which is creating the problem. I took "rock" here to mean that there are no known rock layers or strata because the first set of rock layers was completely ground down and metamorphosed into presently existing layers. If there's no layer you can't say how it was formed; and also you probably won't recognize or be able to date any boulders from the earliest days that may be existing as inclusions in later layers. However these zircons can be dated. There's an all time greatest geology book Annals of a Former World by John McPhee that has a lot about zircons.
This is the earliest, most exciting era, mainly because there are no known rocks.
It makes sense if you argue he/author is mixing two ideas: one, less geologic study of the first two billion years and two, his specific work with crystals in the no known rocks period - the fist 500 million years of the first two billion years. The earliest era certainly begins with no known rocks even though they show up later in the period...
Rocks contain minerals, sometimes much older than the rock itself. So the oldest known rock is younger than the oldest known mineral. The oldest zircons have been recycled through sedimentary and metamorphic processes into their current rock. They're survivors.
Sounds like old white guy geoscience. Not very inclusive. Plus everyone knows that time started in 1996.
Yes, my first two billion years were the happiest.
Everything's gone down hill for the last few million or so.
Must be old age.
At this point, what difference does it make?
I got that the detection ability has advanced by a factor of 10. I assumed that allows them to analyze more precisely the inclusions in the Zircon particles, thus obtaining better information about the local environment of that time.
Increase in detection or similar can be a big problem, as it opens the door for previously unavailable information and resultant responsibility to understand/describe that information and how it fits with current or older conclusions. I am a chemist and am currently seeing limits on bad actors in polymers, etc being lowered to levels I though were ridiculous just 20 years ago due to advances in concentration, detection and characterization . It's a good thing, but an expensive thing for companies who make the involved products. I'd argue, it is a moral responsibility.
"Professor’s study of ancient crystals sheds light on earth’s early years"
Speaking of Marianne Williamson...
Do you think Alexander and Stephan Sobolev are closely related?
The quote in the title is fubar. I think what the person was trying to convey is that we have found zircons, which are tiny mineral crystals, which are 4.4 billion years old but have yet to find the rocks from which they eroded. Perhaps those rocks no longer exist, but they're being searched for.
I have been studying (as an amateur) the Archean (2.5 to 4 billion years ago) rock formations of the Great Lakes region for many years. But the Hadean, that's truly terra incognita.
Cool stuff. Thanks.
I understood the inclusions to be microscopic bits of the original magma, which was our earth about 4.54 billion years ago, trapped in the zircons when they formed. The inclusions were not rock but the elements which later formed into rock. I wasn't clear how they are able to determine the age -- I knew nothing about geology but from what I am seeing the oldest rocks are about 4 billion years old. Interesting fact: In January 2019, NASA scientists reported the discovery of the oldest known Earth rock – on the Moon. Apollo 14 astronauts returned several rocks from the Moon and later, scientists determined that a fragment from one of the rocks contained "a bit of Earth from about 4 billion years ago." The rock fragment contained quartz, feldspar, and zircon, all common on the Earth, but highly uncommon on the Moon.[4] wiki
Dark blue zircon is often used as a substitute birthstone for December.
According to Northwest Exposures: A Geologic Story of the Northwest by David Alt and Donald W. Hyndman, the continental crust formed between 3.5 to 2.7 billion years ago.
In North America the continental crust is exposed at the surface in part of northern Wisconsin, northern Minnesota, most of eastern Canada, and some relatively small spots out west in Montana, Wyoming, and Idaho. But the greater part of the continent still has continental crust underneath it even if it is pretty far down and relatively inaccessible. So the quote about having no rocks from the first 2 billion years seems quite wrong, since we actually have enormous amounts of it.
On the other hand, consistent with the 2 billion year quote, there are large regions where the exposed continental crust, or basement rock, if any, formed 2.7 billion years ago which would mean 1.9 billion years with no surviving rocks. In the region covered by the book above, that is Washington, Oregon, Idaho, Utah, Montana, and Wyoming, the oldest exposed continental crust is 3.3 billion years old, which would leave 1.3 billion years without any known rocks.
So it's probably quibbling to complain about the 2 billion year quote.
"Northwest Exposures" has this to say about the topic:
Formation of the earliest rocks marks the beginning of Precambrian time. The world of Precambrian time is gone, vanished into the depths of space and the abyss of time. The earth has kept a few enigmatic rocks as souvenirs of its early days, but they tell us very little, and very little of that seems familiar.
Beloved Commenter AReasonableMan said...
There is something wrong with this quote, the oldest known rocks are 4.28 billion years old. There are fossils that 3.5 billion years old.
I know math is hard for you, but 3.5gya is more recent than 4.3gya, by about 800 million years. The oldest rocks are 800 million years older than the oldest fossils. What, exactly, is wrong with that? Maybe it's something that only someone of your, erm, unique reasoning ability could understand?
I suspect that Original Mike has it right. A search for "oldest dated rocks" on Winkiepedia yields an article that describes, among others, rocks believed to be much older than 2B years in Canada and Africa. I remember reading about finds in Africa years ago. Of course, the proposed datings are always subject to controversy.
Sadly, "Science" journalism is a sorry thing, much of the time.
Very well written articles on current science and math research topics can be found at https://www.quantamagazine.org/, which should be comprehensible to interested persons who were awake and alert during math and science classes in high school. There's always something good to read there.
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