General Planetary Geology Q&A

Q: To Whom It May Concern

I’m not a scientist, however I find it an interesting issue.

I have a few questions of which I hope you can clarify for me:

– Preben P

 

A: I’ll try to respond to each of your questions below in CAPS:

Q: 1: How does the inner core of the earth maintain its temperature? Or is it decreasing?

A: FOR ONE THING, THE CORE OF THE EARTH IS WELL INSULATED WITH VAST VOLUMES OF LOW-THERMAL-CONDUCTIVITY OVERLYING ROCK. EVEN WITH CONVECTION IN THE MANTLE (AND PERHAPS THE OUTER CORE ALSO) IT TAKES A LONG TIME FOR HEAT TO ESCAPE. WHETHER THE TEMPERATURE IS INCREASING OR DECREASING IS A MATTER OF CONJECTURE. SOME OF THE HEAT IS FROM KINETIC ENERGY DUE TO THE AGGREGATION OF THE PROTOPLANETARY DISK, WHICH WOULD IMPLY COOLING. HOWEVER, MUCH OF THE HEAT IS THOUGHT TO BE FROM DECAYING RADIOACTIVE ISOTOPES… WHICH WITH THE ONSET OF CONTINENTAL DRIFT (MANTLE CONVECTION) IN THE PRECAMBRIAN IMPLIES INCREASING HEAT. MANKIND HASN’T BEEN AROUND LONG ENOUGH TO TELL THE DIFFERENCE. 

Q: 2: After any volcano eruptions what happens to the void space from whatever is discharged?

A: USUALLY A CALDERA REMAINS – A LARGE SUNKEN CRATER – OR SOME OTHER COLLAPSE FEATURE APPEARS. OVERLYING LITHOSTATIC PRESSURE GUARANTEES THAT NO VOIDS REMAIN INSIDE THE EARTH – THERE IS NO VOID SPACE ANYWHERE IN THE EARTH EXCEPT FOR VERY SHALLOW CAVES CAUSED BY LIMESTONE DISSOLUTION (KARSTS). 

Q: 3: Could it be possible that earth is a dying sun meaning that the earth for billions of years ago was a burning planet from big bang? Just like the sun as we know it today.

A: THE SUN AND EARTH DID NOT BEGIN TO FORM UNTIL ABOUT 9 THOUSAND MILLION YEARS *AFTER* THE BIG BANG, SO THE EARTH IS NOT HOT FROM THE BIG BANG (AT LEAST NOT DIRECTLY). AS AN ASIDE, EARTH IS NOT A SUN.

NOTE: a thousand million = billion in America. A million million = a billion in the UK.

THE SUN IS USING UP ITS HYDROGEN FUEL AT A RATE THAT WILL LEAD TO A NOVA IN ABOUT 5 THOUSAND MILLION MORE YEARS. THERE IS SOME EVIDENCE THAT THE EARTH WENT THROUGH A FROZEN “SNOWBALL” STAGE IN THE ARCHEAN EPOCH (MORE THAN ~2,500,000,000 YEARS AGO), BUT THIS IS POORLY UNDERSTOOD (THE EVIDENCE IS TRULY ANCIENT). THERE IS EVIDENCE (STROMATOLITE FOSSILS) THAT THE EARTH RESIDED IN A TEMPERATE ZONE LIKE TODAY AS FAR BACK AS ~3,400,000,000+ YEARS AGO.

Q: Climate change:

Don’t believe its cause by man; for sure man is the cause of poor air quality.

A: IF YOU DON’T ACCEPT THE VAST AND GROWING EVIDENCE FOR CLIMATE CHANGE, THEN YOU ARE PART OF A VERY SMALL MINORITY AMONG EDUCATED PEOPLE. 

MORE THAN 98% OF SCIENTISTS WHO STUDY CLIMATE CHANGE AGREE THAT THE EVIDENCE STRONGLY INDICATES THAT MAN IS THE CAUSE OF CLIMATE CHANGE. THE RAPIDLY GROWING CO2 IN THE ATMOSPHERE, A WELL-MEASURED GREENHOUSE GAS, HAS AN ISOTOPIC SIGNATURE LOW IN CARBON-14: THIS MEANS MOST IF NOT ALL OF THE NEW CO2 WAS SEQUESTERED FOR A MINIMUM OF 50,000 YEARS AS BURIED HYDROCARBONS, AND MORE LIKE HUNDREDS OF MILLIONS OF YEARS. IT IS RELATIVELY EASY TO CALCULATE THE AMOUNT OF FOSSIL FUEL BURNED IN THE PAST CENTURY, AND TIE IT TO THE INCREASE IN CO2. HOWEVER, THE HUNGER FOR MEAT PROTEIN HAS ALSO MEANT AN EXPLOSION OF DOMESTIC RUMINANTS (SUCH AS COWS) THAT EMIT VAST AMOUNTS OF METHANE, A GREENHOUSE GAS UP TO 37 TIMES MORE POTENT THAN CO2. ONE COW EMITS AS MUCH METHANE IN ONE DAY AS THE VOLUME OF THREE OF MY FILING CABINETS. MULTIPLY THAT BY 37 TO GET THE EQUIVALENT CO2 RELEASE. THE GEOLOGIC RECORD SHOWS THAT THERE HAVE BEEN CLIMATE CHANGE EPISODES IN THE PAST, BUT NONE THAT HAPPENED ANYWHERE NEARLY AS FAST AS IT IS HAPPENING RIGHT NOW – IT TOOK HUNDREDS OF THOUSANDS OF YEARS INSTEAD OF OUR CURRENT HYPER-SPEED, CHANGE-IN-A-CENTURY RATE). 

I CONCUR WITH YOU THAT MAN IS DEFINITELY THE CAUSE OF POOR AIR QUALITY. 

Q: How about magnetic poles so when the suns positive pole is close to earths negative it will bring the 2 closer and opposite when negative is close to negative also the moon must have effect there.

A: YOU ARE THINKING OF HOW BAR MAGNETS BEHAVE CLOSE TO EACH OTHER – THIS IS A FAULTY ANALOGY BECAUSE OF FACTORS OF BOTH SCALE, PROCESS, AND DISTANCE. THE SUN IS 144,000,000 KILOMETERS FROM THE EARTH. THE SOLAR WIND *DOES* INTERACT WITH THE MAGNETIC POLE OF THE EARTH (AURORAS). THE STRENGTH OF THE SOLAR MAGNETIC DIPOLE IS FAR TOO SMALL TO INFLUENCE THE EARTH’S MAGNETIC DIPOLE, WHICH IS APPARENTLY DRIVEN BY THERMAL CONVECTION IN THE CORE OF THE EARTH. 

Q: PS: Science is like religion you either believe in it or not, however science has a few fact but if they come off wrong at the start everything is wrong

A: I PARTIALLY AGREE WITH YOUR PS: *SOME* PEOPLE ATTEMPT TO MAKE SCIENCE THEIR RELIGION. I DON’T THINK THAT IS WISE, BUT I UNDERSTAND HOW IT CAN HAPPEN. I AGREE THAT FAULTY SCIENCE CAN LEAD TO FURTHER MISTAKES, LIKE HOW SOVIET GENETICS WAS CRIPPLED FOR DECADES BY THE SO-CALLED STALINIST GENETICIST LYSENKO. HOWEVER, WHILE SCIENCE IS THEORETICALLY A SELF-CORRECTING PROCESS, IT IS NEVERTHELESS IMPERFECT, A VERY HUMAN PROCESS. IT SHOULD THEREFOR NOT BE WORSHIPED. 

IF YOU DON’T BELIEVE IN SCIENCE THAT IS FINE, BUT IT MARKS YOU AS SOMEONE WHO HAS NOT STUDIED AND LEARNED ENOUGH TO UNDERSTAND IT. YOU CAN ALSO CHOOSE TO NOT BELIEVE IN GRAVITY, HOWEVER IF YOU THEN STEP OFF THE TOP OF A BUILDING YOUR BELIEF WILL NOT MAKE IT GO AWAY. 

One final comment. Everyone is entitled to an opinion. However, if you base your life and actions on opinions not backed up by facts, you will not live long nor well. MAKING UP facts doesn’t make them facts. You can believe that 1 + 1 = 3 but your orbital mechanics BASED ON THAT MATH will not land a man on the Moon. 

Red Rocks and Green Rocks and Blue Rocks…

    Some questions begin with a profound basic misunderstanding – but people are still trying to make sense out of their world, so I am grateful that they even ASK the questions.

Q: At the age of 40 I am slowly figuring out geology just because I’m curious. 

     One of the things that caught my attention in Dr. Robert M Hazen’s The Story of Earth is that the mantle is green: peridotite, olivine, perovskite, etc. That surprised and delighted me, because introductions to Earth science tend to show the Earth in cross section with a lava-colored mantle and core.
     But when lava erupts, it is usually reddish orange. What happened to change it?
     Is it interaction with water from subducting slabs of ocean floor? Is it because repeated melting has allowed some of the heavier elements to sink away instead of reaching the surface, changing magma’s chemical composition? Has it oxidized, in which case the Moon’s maria and other airless objects in the solar system might’ve been green when they were molten? Or is the lava that erupts on the surface  from some other source than the mantle? 
     Thanks for answering our questions. An answer I got from you many years ago helped start my geological journey (I asked whether there could’ve been continents on the other side of the planet from Pangea that had subducted; you explained that continental rock is less dense than ocean floor so it doesn’t subduct. Hazen’s book helped me understand WHY it’s less dense.)
Regards,

– Ellen B

A: Good on you for actually thinking about these sorts of things.
    SOME mantle-derived rocks are green at the surface because they have significant chlorine content. However, Kimberlites, the long tubes that reach down to 100+ km depths and bring diamonds to the surface of the Earth in places like South Africa, South America, and Arkansas, are famous for being blue in color. It just means different minerals (like chrome diopside) dominate in Kimberlites. Many other mantle-derived rocks are black or gray – and often weather to brown, hence the origin of the name for one rock-type: dunnite, after the color dun originally used to describe certain beige-colored cows. 
    These colors are all what you see at ambient temperatures that exist at the surface of the Earth. However, the deeper you go into the Earth, the higher the temperatures are – this is the geothermal gradient. It’s sort of like a biscuit coming out of the oven: the outside quickly cools and chills to a crust, but bite into it too soon and the inside will burn your mouth.
    When you see a red or yellow color in magma, it’s because of the TEMPERATURE. This is black-body radiation, a basic physics principle. I’m attaching a photo of me next to what we informally called the “Cookie Monster” in Hawai’i. 
 

 

 
    The black-gray structure is a Hornito – basically a lava splatter-cone. The glowing “mouth” is a Skylight – a hole broken into the top of a lava-tube. We have used a police speed-gun to measure the speed of the lava running past and beneath this skylight: it was moving at 40 km an hour (25 mph). The whole thing collapsed about a month after that photo was taken, by the way – not a good place to be standing.  The grimace on my face is because the air temperature where I am standing was above 60 C (140 F). That blue cloud to my right is H2S gas, which engulfed me just after the photo was taken. My gas mask was on me at the time – but not adjusted to my face – and it turned my nose and throat mucous membrane fluids into sulfuric acid.     
    Translation: my nose and throat felt like they were on fire, and I took off running to get away from the cloud. 
    The colors you see correlate with temperature: red is centered around 4,000 K and yellow is centered around 6,000 K. You may have seen the dull red in a toaster: same thing is happening.
    If you could actually “see” rocks at the 30 – 50 km depths where this lava arose from, they would be yellow or even blue-ultraviolet at deeper depths.  
    Hope this helps you “see” (understand) the different reasons for rock colors. 
~~~~~

Earthquakes: How Often? 

Until the following question arrived, I had only thought of earthquakes as being relatively localized features, mainly occurring along continental margins and ocean-floor spreading centers or transform faults. The San Andreas fault is a mostly on-land transform fault. I hadn’t really thought about how MANY earthquakes there are in the world as a whole.
Q:
Hello, I was wondering how many earthquakes happen typically in a year?
-Lauren JA:

The USGS estimates that several million earthquakes occur in the world each year. Many go undetected because they hit remote areas or have very small magnitudes. The National Earthquake Information Center in Denver, CO, now locates about 50 earthquakes each day, or about 20,000 a year. There are far fewer large events than small earthquakes, and this website will show you how these are parsed out according to magnitude:
http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

There are lots of fascinating stats here, including an interesting table (below). Like asteroid impacts and frequency, or volcanic eruption magnitude and frequency, these all seem to follow an inverse log law:

The bigger the event, the less common it is.

Frequency of Occurrence of Earthquakes

Magnitude Average Annually
8 and higher 1
7 – 7.9 15
6 – 6.9 134
5 – 5.9 1319
4 – 4.9 13,000
(estimated)
3 – 3.9 130,000
(estimated)
2 – 2.9 1,300,000
(estimated)
~~~~~