Posted by DrJeff on June 13th, 2009
Copyright 2009 | About this blog
This post is a Driving with Jordi.
This is crossposted at Huffington Post HERE.
Note to reader: click on the links in the text for the real data. This is not a work of fiction.
From Dr. James Hansen, Director of the NASA Goddard Institute for Space Studies concerning this postâ
Public understanding of climate change depends on an understanding of time scales. Goldstein [Dr. Jeff] does a brilliant job of making clear the rapidity of the human-made intervention in the climate system, and the correlation of global warming with the appearance of technology powered by fossil fuels.
âDaddy, how long is a billion years?â
As soon as we got in the car this morning, and buckled up, I said âso Jordi, I need some help. I need more material for the blog.â âDaddy, what do you mean by âmaterialâ?â Â âThatâs what writers call the stuff they use to create storiesâ, said daddy.
It was a beautiful, sunny morning, so he started talking about âŚ the Sun. He had lots of questionsâwhere did it come from, whatâs burning on it to make it so bright, how old is it, what will happen to Earth when it stops burning? The last one was particularly cool. I asked him if he thought the question “what will happen to the Earth when the Sun dies?” is something lots of kids might ask. He said âyes!!â I asked him who he thought was the first person to actually figure it out. He didnât know. I told him it was me.
When I was a grad student at Penn, one of the undergrads in the class I was teaching asked that question. I didnât know the answer, so I told her Iâd find out. I tried but I couldnât. Nobody had done it before. So I decided to be the first. I didn’t know if I could, and I didn’t know what I’d find, but it was incredibly excitingâand thatâs science. Here’s the result. (And it was far from the end of the story.)
Jordi said, âYOU DID?â I looked at his surprised face in the rearview mirror and said âyup, your daddy.â Then he said, âthatâs sooo strange! That’s sooo cool! I asked a question that YOU figured out!!â He was very proud. I felt so connected to him. (Weâll see later if he told his friends.) And I promise that Iâll make this story into a blog post, because now YOU’RE waiting for the rest of the story.
By the time we arrived at the school 20 minutes later, I had a monthâs worth of âmaterialâ for Driving with Jordi (stay tuned). The conversation was incredible. At one point though, Jordi ran into a conceptual wall when I was talking about the Sunâs lifetime being 10 billion years, and that itâs now half way through its life. He said âDaddy, how long is a billion years?ââwhich is why I wrote this post.
It is actually such an important question, and I thought about it all the way home. It’s at the heart of a key recurring problem in science education in that the VAST majority ofÂ humans truly donât understand lengths of time that are far longer than our lifetimes. No wonder that folks donât understand global warming as due to human intervention, and think it reasonable to interpret the data as explained by natural variation in the environment over long timescales. No wonder that folks donât understand the timescales for evolution of species.
So here now is a novel way to look at it. Thanks Jordi! I think this will help lots of folks understand something theyâve never understood before.
Humans and Time
We humans now live on average about 75 years (in the developed world; in Africa the life expectancy is frighteningly low at 32 to 55). I’ll assume that 75 years is the life expectancy of a human in the absence of devastating diseases like AIDS, and with the availability of modern medicine.
We humans also like to perceive the passage of time in units of seconds, minutes, hours, days, weeks, months, and years. Weâve created these units because they are comfortable, connected to the rhythms in the sky and in our bodies, and each is used to make sense of events both short and long.Â Hereâs the critical point for the rest of the storyâ
One of our average humans sees 75 years x 365.25 days/year =
27,394 days in their life
That’s amazing. Thatâs 27,394 days of getting up in the morning, eating, working, playing, relaxing, and going to bed. Put this way, the length of a single day is absolutely inconsequential relative to a human lifetime. Agreed? Good.
A Really Cool Diary
So letâs say I had this really cool diary with one page for every day of our average humanâs life. Itâs a single book with 27,394 pages. I could give it to you at birth and ask you to record your life one pageâone dayâat a time (with some help from a friend in your early and possibly later years). Like I said, one cool diary.
A Day in the Life of the Earth
Letâs say planet Earth was this large cosmic creature. Sheâs got a life expectancy of about 10 billion years, from her birth with the Sun nearly 5 billion years ago, to her ultimate fate when the Sun is in its waning years some 5 billion years from now (nope not telling).
Earth obviously has a lot to say, and SHE’s been keeping a diary since she was born. But she’s got it in far too many volumes, since each didn’t come with many pages, and they’re all old and worn out. Hey,Â I think a new diary is a perfect gift for her!Â Iâll give her one of my really cool diaries with 27,394 pages. I’ll help her move all her old diary entries into the new one so it will trulyÂ record her 10 billion year life.Â Why donât we call each page a GEOLOGIC DAY (a Dr. Jeff made-up term.) And every Geologic Day is absolutely inconsequential relative to Earthâs lifetime. After all, Earth has 27,394 of them.
Every Geologic Day, Earth will write in her diary the comings and goings for that day. Hereâs the next important pointâ
Every one of the 27,394 pages in Earthâs diaryâeach Geologic Dayâ
isÂ 365,000 years long
enough time for 14,600 human generations
How come? Easy: 10 billion years divided by 27,394.
Take a minute to process that.
I hope this gives you a new perspective for spans of time for Earthâcalled geologic timeârelative to the time span for our fleeting lives.
So I give my friend the Earth one of my cool diaries. She likes itâher life all in one book. I also happen to be very close with Earth, and sheâs letting me look at her diary. So here we are in the middle of her life and she just now finished her entry for day 13,697. Sheâs already written the first 13,696 pages (I helped her transfer the entries from her old diary with Apple Time Capsule.) Here now is her page 13,697â
You can really make this a powerful visual demonstration in class. The life of Earth recorded on 27,394 sheets of paper is a challenge to demonstrate. But if you can borrow some cartons of xerox paper, with each carton containing typically 10 reams, then here is what I’d do. Each ream contains 500 sheets. So you need 5 full cartons (that’s 50 reams = 25,000 sheets) + 4 reams (another 2,000 sheets) + 394 sheets.
Without telling the class anything about what you are doing, have them take the reams out of the boxes (without opening them) and lay them out on the floor. Have them open one ream to see how many sheets are in it. In fact, have them count the sheets in the ream and take out the 394 sheets you need. Then:
â˘Â walk them through the concept of a single diary for an average human lifetime: they should calculate how many diary pages they would need if there is one page per day; then have them calculate how many sheets are on the floorâ”oh, the number of days in a human lifetime! Â WOW!! Â That’s a lot of days for a human!”
â˘Â let them in on the idea of giving this diary to Earth, and assuming a lifetime of 10 billion years, have them calculate how many years of history are on EACH sheetâ”365.000 years! No way!!” Then have them calculate the equivalent number of human generations on one sheet assuming 25 years per generation (a reasonable time from parent birth to child of parent birth)â”Can that be right? 14,600 generations!?”
â˘ re-arrange the paper with half of it on one side of the floor to represent Earth’s history that is already recorded,and the other half on the other side of the floor representing Earth’s future history.
â˘Â then pick the single sheet of paper that represents the last 365,000 years of history, so that on this sheet, the final diary entry is the present. Lay it between the two groups of paper representing the past and future history of Earth.
Ask the class to think about this sheet of paper as a 24-hour clock. So at time 0:00:00, you’re at the beginning of the sheet, 365,000 years ago. At time 12:00:00 you’re in the middle of the sheet 182,500 years ago. At time 24:00:00 you’re in the present moment, where you all happen to be sitting in class.
Ask them to calculate the time on the clock when human civilization began (10,000 years ago, answer: at time 23:20:19); when the industrial age began (the age of fossil fuels; 150 years ago, answer: at time 23:59:25).
Have them look at world population growth noting what’s happened during the age of fossil fuels, the carbon dioxide level over the last 650,000 years, and the world temperature over the last 2,000 years. What is the data telling you?
â˘ have them figure out how many sheets ago the dinosaur extinction took place.
â˘Â have them research Earth’s geological history, and figure out which sheets contain other milestones or important intervals in Earth’s history.
This should be MIND BLOWING! It is an experience your students will likely remember for a lifetime.
Photo caption: Earth from MESSENGER spacecraft as it flew by Earth on August 2, 2005. MESSENGER goes into orbit around Mercury on March 18, 2011.
Image courtesy NASA, Johns Hopkins University Applied PhysicsÂ Laboratory, and Carnegie Institution of Washington.
5 Responses to “A Day in the Life of the Earth: Understanding Human-Induced Climate Change”
Jeff Padgett Says:
October 1st, 2009 at 9:56 am
I would like to know exactly how carbon dioxide acts as a greenhouse gas, even though it is only present in trace amounts. Is it something about its molecular geometry or what? I’m not a global warming denier; I just want to understand how the process works.
October 6th, 2009 at 9:59 am
Hi Jeff P.-
The basic concept is that energy in the form of visible sunlight streams through Earth’s atmosphere and heats the surface. Here is an important point – all objects at planetary temperatures (like you and me – and the surface of the Earth) give off (radiate) a different flavor of light called infrared light. You often hear folks refer to this as heat radiation. So the energy in sunlight absorbed by Earth’s surface is then re-radiated out as infrared light. If it wasn’t, the surface would keep heating up to higher and higher temperatures as Earth would be unable to dump the energy it continuously receives as visible sunlight. Now here’s the problem – there are gases in the atmosphere that absorb infrared light coming from the surface. It is a characteristic of the molecules of these gases. These are the ‘greenhouse gases’. They then re-radiate the infrared energy they’ve received, and a chunk of that goes … back to the surface. The net effect is that the greenhouse gases make it more difficult for Earth’s surface to re-radiate back into space. The result is a new equilibrium is reached where energy in to Earth = energy out at the top of Earth’s atmosphere, but the price Earth pays is a higher surface temperature than if the atmosphere with its greenhouse gases wasn’t present. There is actually a natural greenhouse effect, with Earth’s surface temperature higher because of the natural greenhouse gases in the atmosphere. The concern is the ADDED greenhouse effect caused by the greenhouse gases humans have been pumping into the atmosphere since the beginning of the Industrial Revolution. Let me know if this provides the basic understanding. I also know it will raise lots of questions, e.g.: why does CO2 as a trace gas place such a great role? How do we know CO2 is a greenhouse gas? So I wanted to provide a link to a history of scientific understanding of the role CO2 plays in global warming. Here an American Institute of Physics web page you should read: http://www.aip.org/history/climate/co2.htm
Dr. Heather Good Says:
October 22nd, 2009 at 10:09 pm
I tried to think of something I had ever seen 27,394 of at one time as I don’t have 50 reams of paper here. A few years ago my Girl Scouts did a penny drive and we had to separate Canadian and US pennies in our donations and then roll them into tubes of $.50.
We sat down with a pile of $220 dollars in pennies, not quite the $273.94 necessary for your experiment, but close. It required two dozen girls over two hours to sort and roll them all after spreading them layers deep across eight big tables. We carried them in about 10 pails and each pail was very heavy as 22,000 pennies weighs around 66Kg. We counted out 440 rolls of 50 pennies to take to the bank and we spent it all on an exciting camping adventure. One penny – so inconsequential – but 22,000 Geologic Days of them? – powerful enough to create a world of fun for two dozen girls.
October 23rd, 2009 at 7:21 am
Hiya Heather! That’s a wonderful example of how the learning experience for this post can be reframed in other powerful ways.
Ted Magnuson Says:
October 23rd, 2009 at 4:06 pm
Disbelief in the toxicity of carbon dioxide is one thing, but consider too, how the population is expected to reach 7 billion soon. It was only 3 billion in 1960. Unless something drastically compassionate and widely supported happens soon, what will life on earth be like by the year 2050. Can the earth support 20 billion people. Talk about cap and trade!!!