27

key concepts

27.1

Primary Endosymbiosis Produced the First Photosynthetic Eukaryotes

27.2

Key Adaptations Permitted Plants to Colonize Land

27.3

Vascular Tissues Led to Rapid Diversification of Land Plants

A Toxic Spill of Ancient Fossil Algae

In the Gulf of Mexico, about 60 kilometers south of the Louisiana coast, the oil rig Deepwater Horizon was drilling an exploratory oil well in the seafloor beneath about 1,500 meters of water when, on April 20, 2010, an explosive blowout occurred and could not be contained. Over the next 3 months, almost 5 million barrels of petroleum flowed from the well into the Gulf, making this event the worst marine oil spill in history. The spill caused massive mortality among marine life, as well as considerable damage along the coast as the oil floated to the surface and washed ashore.

Why was oil to be found so deep beneath the Gulf, and what led geologists to expect to find oil there? Most people know that petroleum is a fossil fuel, meaning that it is derived from the ancient remains of once-living organisms. Fewer people know that most petroleum is derived largely from the remains of phytoplankton, including many species of green algae (as well as other microbial groups, as discussed in Chapter 26). These algae produce complex hydrocarbons through photosynthesis. They accumulate hydrocarbons both as an energy reserve and as a way to increase their buoyancy in water. When these algae die, they drop to the bottom of the ocean, and over many millions of years, their buried remains decompose into petroleum deposits.

Today there is great interest in using solar power to help meet human energy needs. But unicellular eukaryotes capitalized on this process first, and very long ago. Single-celled eukaryotes incorporated tiny solar energy converters into their cells about 1.5 billion years ago, when they formed partnerships with photosynthetic cyanobacteria. These endosymbionts—which over time would become the chloroplasts of modern plants—allowed many eukaryotes to use solar energy to drive the reactions that convert carbon dioxide into organic carbon compounds. Over many millions of years, the carbon compounds produced in the cells of marine algae accumulated in ocean sediments. Today humans are tapping that trapped solar energy in the form of petroleum and other fossil fuels.

Given that petroleum is derived naturally from green algae, can humans use green algae to produce oil commercially?