LAST LECTURE  The modern configuration of land, ocean and climate: The Holocene Epoch

Focus Question:  How does the Holocene differ from previous interglacials?

1.        We have made our climb to the top of the Geologic Time Scale, and now we have reached the Holocene Epoch.  The Pleistocene and Holocene Epochs are the two epochs of the Quaternary Period on the old Tertiary/Quaternary division of the Cenozoic. 

a.        The Holocene is the interglacial stage  following the last glacial stage-the most recent ice age.

b.      The Holocene began 11,700 years ago, and continues to this day.

c.        The Holocene has similar features to other interglacials.  Pre-industrial Sea level and atmospheric CO2 levels are about the same as other interglacials.

2.       As the ice melted back following the last glacial maximum,

a.        The modern Great Lakes formed in North America

b.       The sea level rose to its present level, rising rapidly until about 6,000 years ago, then very slowly (cm/yr) after that.

3.       We now must consider the other kinds of variation that operate on much smaller scales than the glacial-interglacial  cycle.  Small variations in incoming solar radiation from the sun drive small cooling or warming events on the century scale.    The Sun varies in its amount of heat that it produces, and it does this on much smaller scales than the glacial/interglacial cycle. 

a.        The sunspot cycle (sunspots are magnetic storms on the sun’s surface, and indicate episodes of more heat output) is 11 years  in duration

b.      Sunspot cycles occur in bundles of about 80 to 100 years, called Gleissberg Cycles

c.       These variations are on the human and historical time scale, and although they are not big and dramatic, they still affect humans and impact society

4.        Examples of these kinds of impacts include

a.        The Medieval Warm Period (from about 900 AD to 1350 AD) when the sun was more active, and regions of the northern hemisphere were warmer than today

b.      The Little Ice Age (from about 1350 AD to 1850 AD) when the sun was less active, and regions of the northern hemisphere were cooler than today

5.         A question that we can ask, at this point in our view of the entire Geologic Time scale, is, when in Geologic Time was atmospheric carbon dioxide as high as it is now?  Carbon dioxide as of January, 2014 is measured at 400 ppm (you can find these measurements here and check out their interactive Historical view of rising CO2) http://www.esrl.noaa.gov/gmd/ccgg/trends/global.html .  How can we answer this question?

a.       We can look at the CO2 measurements from ice cores drilled in the Antarctic and Greenland Ice Sheets.  Slices of these cores contain tiny air bubbles that can be sampled for the air inside them.  CO2 can be measured. 

b.      Our pre-industrial (around the 18^th century) values are about 280 ppm, very similar to the CO2 values in the previous 4 interglacials, including the last interglacial, about 125,000 years ago. 

c.       Our post-industrial CO2 rises after that to its modern value of 400 ppm.

6.        We have to go back further than the last interglacial (about 125,000 years ago) to see a time when CO2 values were as high as they are right now.  We have to go back to the Pliocene Epoch   to see similar values, and that is about 5 million years ago. 

7.        Human population (now approaching 7 billion) is an obvious difference between the Holocene Epoch and anything previous.  Thus, natural variations, like the changes in incoming sunlight (orbital changes, solar changes) are also combined with the impact of human activities.  These include

a.        Burning of fossil fuels (coal, oil, gas) which releases carbon in the form of CO2 into the atmosphere

b.      Agriculture, which releases methane (CH4) into the atmosphere. 

c.  growth of huge cities, with the use of natural resources to fuel that growth

8.        We can answer today’s focus question, then and see that the Holocene is in some ways a typical interglacial, but with the obvious difference of having the added impact of a large human population.  When we look back upon the whole Geologic Time Scale, we can see how many of the aspects of the modern world we live in are legacy effects of events and processes in the past.

We are now in uncharted waters, in the sense that although we are in an interglacial, the many differences we make as a human population (and a large one!) on the planet make substantial differences in the way the Earth responds (after all, WE are the ecology, too!).  Although the future events we encounter may be unique, the processes that drive them will be quite recognizable to you.  You have seen the processes and patterns of the Earth's record, and you will recognize them, even as the events that occur may be unique.

 This ends the course in Earth History.  Have a great year!

Reminders:         the Final Exam will be available online beginning Monday December 8th at 8 a.m. through Friday, December 12th at 6 pm.   The exam will be open book/open notes.   The exam is multiple choice, about 50 to 60  questions, and draws mostly from the question pool for the quizzes and the midterm exams.