As we saw from the O18 graph of several days ago, the Earth's average temperature has been cooling for the last 5 million years -- along with astronomically-driven cycles of more modest warming and cooling. In fact, the O18 data from cores show that the Earth has been slowly cooling for the past 40 million years. Why?
One of the most promising theories is the "uplift-weathering hypothesis", which you may have seen described in a British-produced NOVA program some years ago.
Here's the deal.
About 50 million years ago, India, having broken away from the southern supercontinent of Pangea, drifted north and began to collide with Asia, gradually forcing up the massive Himalayas and Tibetan plateau. This has been well-documented by land geologists.
Up go the mountains, drenched on their southern face by Indian Ocean monsoons which have been intensified by the uplifting plateau.
As the mountains rise, mechanical erosion (steep slopes and running water) and chemical weathering cut them down.
Here's the equation for chemical weathering (again, I should use subscripts, but I won't):
CaSiO3 + CO2 >>> CaCO3 + SiO2
Silicate rocks (CaSiO3) combine with carbon dioxide (CO2) from the atmosphere -- which has dissolved in rainwater making a dilute acid-- to yield calcite (CaCO3) and silica (SiO2). These dissolved chemicals are carried to the sea by rivers…
…where planktonic organisms incorporate them into their microscopic skeletons -- forams and coccoliths thrive on the carbonate, and diatoms and radiolaria flourish on the silica.
The organisms die, fall to the bottom of the sea, and are buried in the ever-deepening layers of sediment.
The net result is that CO2 is taken out of the atmosphere and buried in the sea floor, on a much more massive scale than would occur without the uplift.
And...the planet cools as the "greenhouse effect" is diminished. Voila! Ice ages.
The JR cores into the sediments near the rivers' mouths and in the deep ocean to provide the data that tells the story.
Human curiosity, telling the story of the Earth that is buried in seafloor sediments -- a story of drifting continents, mountain building and destruction, living organisms "feeding" on the detritus of mountains, declining CO2, cooling climate, ice advancing and retreating, all taking place over tens of millions of years.
Human curiosity discovering the story of the planet's past, piecing together a thousand clues from land and sea. Let BP look for oil and money beneath the sea floor. The vessel I'm sailing on, the JOIDES Resolution, is an exquisite instrument of pure curiosity, an investment by you and me in the questioning spirit that makes us human.
Here is a partial map showing sites were the JR has sampled the planet's past -- and illuminated possible futures. Click to enlarge.