The close approach of the moon had a staggering impact on Earth’s volcanic heat balance. One outcome was the Siberian Traps. Even today volcanic activity caused by the once closer moon is a substantial part of our dynamic biosphere. During the terminal Permian extinction, tidal heating led to the beginning of a series of massive flood basalts. These flood basalts have often been compared to the mare on the moon. Tidal friction caused the lava to erupt from within the earth.
Traps is a Swedish term used to describe the stair stepped appearance of continental flood basalts. Flood basalts are different than the typical lavas associated with Earth’s subduction volcanoes. Whereas subduction volcanoes form cones, flood basalts form large flat “floods” of basalt. These build on top of each other, building layer upon layer, thus the name traps. Continental flood basalts cover huge areas and can be thousands of feet deep. The Siberian traps for example are 10,000 feet thick.
The Siberian Traps are the greatest known flood basalt on Earth and were unprecedented; nothing like it had been seen on Earth in eons. The Siberian traps were erupted onto the ancient continent of Pangea and very well may have been part of the initial disruption and break up of the great continent. These flood basalts are similar to mid ocean ridge volcanism, which are the engines of continental rifting and spreading.
The important thing to note is that flood basalts mirror the pattern of dissipation of tidal heating energy, as seen throughout the solar system. As the cycle of tidal heating changes through time, layer upon layer of flood basalts build up the trap surface. There have been 11 major flood basalt events continuing into the present. These flood basalts have, through time, decreased in intensity, reflecting a retreating moon. The most recent flood basalt is the Columbia River flood basalt which has covered much of eastern Washington and Oregon. The hot spot volcanism associated with Yellowstone National Park is thought to be a lasting legacy of this most recent flood basalt. The north American plate has moved westward over the hot spot so that now its activity is seen in the park in Wyoming.
The Siberian traps and Permian extinction essentially happened at the same time. It is generally assumed that the Siberian traps (and the associated basalt flooding, eruptions, and off-gassing) was the major contributor to the Permian extinction. The volcanic off-gassing of this massive flood basalt would have had a devastating impact on both the atmosphere and oceans of Earth. But there is no good explanation for why this sudden eruption of flood basalts happened. Why after billions of years of geologic calm did the earth suddenly, volcanically erupt back into life again?
The only known source of planetary reheating is tidal heating and the product of this heating is serial basalt flooding. The best explanation for how the flood basalts on Earth were produced is this very process of tidal heating. The close approach of the moon can and does present the only reasonable means of re-energizing the earth. Ultimately this led to the greatest extinction in the long history of life on earth.