Evolving timescale

The names of geologic periods on the geologic timescale we use today represent an international melting pot of terms derived from earlier efforts to divide up the history of the Earth. The period names Triassic and Quaternary are holdovers from earlier version of the timescale that divided Earth history into three (tri-) and four (quater-) slices. The names for the Periods of the most geologically recent Cenozoic Era continue to evolve. The Tertiary Period has been divided into two periods, the Paleogene and Neogene (meaning, old recent and neo recent, respectively). This fine-tuning permits more precise correlation of rock units around the world allowing for greater detail in our reconstructing the history of the Earth. The chart shown here is the work of an international committee.

Putting a name on time

-->When geologists talk about events that occurred 200 million years ago, they are referring to dates on the geological time scale.  Adding dates to the time scale was made possible with the discovery in the late 19^th century of the use of radioactive decay as a tool for determining the age of geologic materials.

The geological time scale is an evolving document, and radiometric dates are subject to refinement as technology advances.

But the geological time scale has always been an evolving document, even before dates were added. The names of the geologic eras, periods, and epochs on the geologic time scale we use today were not written in stone (so to speak!) but represent the latest version of a document that has its origins in principles enunciated almost 400 years ago.

Figuring out the order in which rock layers were deposited or emplaced was the first step to developing a time scale.

Energy tradeoffs

There is no one easy solution to meeting the energy needs of the 21^st century and beyond; every technology has its trade-offs:

Petroleum and coal are both non-renewable and produce greenhouse gases; solar and wind energy both require lots of land and the energy collected from them can not yet be efficiently distributed; and hazardous waste from nuclear power plants must be dealt with for thousands of years.

Less obvious are the hidden costs of energy sources; biofuels, regarded as the “greenest” technology, uses hundred of liters of water to grow the fuel.

The other side of the energy equation is reducing use, which is an issue that involves education and public policy. The solution to our future energy needs requires the input from scientists, engineers, educators, policy makers, and you.

Science magazine has a special section on scaling up alternative energies and the trade-offs involved.

[Adrian Cho, Science, v. 329, 13 August 2010,p. 786-787]

Image from here.

Geothermal energy, revisited

Volcanoes and geysers bear witness to the enormous reservoir of energy--in the form of heat--that lies in the earth's interior. This geothermal energy can be used to generate electricity wherever there is a source of heat close to the earth's surface. Unlike the non-renewable fossil fuels, geothermal energy will last until the earth's internal engine runs out of fuel, millions of years from now.

But geothermal energy has its limitations as an alternative energy source. Production of geothermal energy is limited to relatively few areas with the required local geothermal source, and drilling to tap these sources can have unintended consequences. A geothermal project in Switzerland was canceled in 2007 after drilling caused a magnitude 3.4 earth tremor.

Source: E. Kintisch, Science 329:789, 13 Aug. 2010

Photo from here, along with a list of "Top 10 alternative energy sources"

Ethanol and policy issues

Recently, the U.S. government increased the cap on the amount of ethanol that can be used in gasoline from 10% to 15%. Upping this limit should encourage the development of alternative sources of ethanol, but changing this limit affects the car manufacturers.

A proposal to require cars to use an E85 blend (that is, 85% ethanol, 15 % petroleum) could be accommodated by car manufacturers, but it is not known whether this ethanol-rich blend would damage engines designed to operate on the current 10% blend.

Scaling up the use of cellulosic biofuel is not just a scientific or technological issue, but a policy issue as well. One scenario would be to have the ethanol limit gradually increase from to 85%; the current increase to 15% is a down payment on this strategy.

Learn more about E85 and "flex fuel" vehicles here.

Photo: an E85-powered Chevrolet HHR.

Growing Green

A major roadblock to scaling up the use of cellulosic biofuel is the difficulty and expense of extracting the ethanol from these materials.

The ethanol currently used in gasoline mixtures come from fermentation of sugars present in corn kernels, and is a relatively simple and inexpensive process. However, the sugar in cornstalks and other cellulosic biofuel is locked in chemical structures that are harder to break and the ethanol yield is lower, which means that manufacturers of cellulosic ethanol require much more raw material than the ethanol manufacturers.

Scientists are exploring ways to extract cellulosic ethanol more effectively. One possible solution is to engineer new microbes that can break down cellulose into sugars that can more easily be fermented to form ethanol.

The Great Lakes Bioenergy Research Center is a consortium of organizations working to conduct this sort of "transformational biofuels research". Go Green!

Biofuels

Ethanol is a fuel derived from plant material, primarily corn kernels. Although a renewable resource, one of the down-sides of using corn-derived ethanol as fuel is that it diverts grain from food to energy use, driving up food prices. This concern was addressed by research into using biowaste, that is, grasses, cornstalks, and wood chips not used for food.

The problem with using this “cellulosic” ethanol is that the ethanol is much harder to extract. Currently, just 40% of the energy content available in cellulosic plant sources is recoverable, compared to 90% of the energy in kernal ethanol.

But another issue with ethanol from corn is that the process requires a lot of energy, and the end-product ethanol does not represent a big savings in the use of fossil fuels in the process and still contributes to greenhouse gas emissions.

More on the pros and cons of ethanol, here.