When Mammoths Roamed Bird Park
The Earth we live on is an ever-changing place. Geological process such as earthquakes, volcanoes, and plate tectonics have been active on our planet for billions of years, and are constantly altering our home. As the Earth changes, climates change too.
Think for a moment about the state of the Earth a mere (by geological standards) 15,000 years ago. Much of the northern hemisphere was locked in an ice age that had seen numerous warming and cooling trends for nearly 2 million years, a time period geologists call the Pleistocene. During this time, there were four major advances (or glacials) of the ice sheets into central North America, and three times the ice retreated back into northern Canada (interglacials). Each glacial and interglacial period lasted for several hundred thousand years.
The fourth, and most recent, glacial reached its maximum extent 15,000 years ago when the glacial ice had advanced to just 30 miles northwest of Mt. Lebanon. The ice front was located along a line from just north of Beaver through just south of Slippery Rock. There, two large lakes formed from meltwater at the terminus of the glaciers; Glacial Lake Watts located at the site of present-day Lake Arthur, and Glacial Lake Edmunds to the northeast (for more information see the PA Geological Survey web page listed below).
What were conditions like in the Mt. Lebanon area during this time? There is little hard data available for this region, however, we can use information available from locations similarly situated with respect to the glacial front elsewhere in Pennsylvania. First of all, the climate was much colder, drier, and windier than it is today. Remember, we were only 30 miles from an ice sheet that extended across to Russia and northern Europe. In fact, the local area was probably a tundra that was rich in grasses and alpine plants with small shrubs and dwarf birch trees. It is possible that this area was also underlain by permafrost, similar to far northern Canada today. The closest true forests were located far to our south, and included spruce trees and alpine plants. Imagine, not a tree as far as you could see in western Pennsylvania.
The animals that lived in the area during the Pleistocene were much different than we know today. Mammoths and Mastodons roamed our local hills. Occasionally, bones or teeth from these animals will be found among the gravels in the Pittsburgh area river beds. There were also bison, elk, saber-tooth cats, horses, bear, moose, lynx, panthers, and of course, insects. Humans were also here as early as 16,000 years ago as revealed by archeological discoveries at Meadowcroft rock shelter in Washington County.
As the glacial event concluded and the ice retreated into Canada, the flora zones advanced northward also. The tundra environment was replaced by spruce trees and herbs. These plants were then replaced by a forest dominated by pines sometime between 10,000 to 12,000 years ago. By about 10,000 years ago, a more modern forest, dominated by oaks, white pines and hemlocks, became established. Today, we are in another interglacial period. The Earth is still slowly warming from the last ice age. Because of this warming, mountain glaciers and ice sheets in Antarctica and Greenland are slowly melting. In turn, sea level is rising, causing coastal erosion and climatic changes. (Did you know that sea level was nearly 400 feet lower 15,000 years ago than it is today?) Although debated by many, the evidence is clear that humans (although not the sole cause) are contributing to global warming with greenhouse gas emissions. The Earth has changed, and will continue to change naturally whether or not we are here. However, we must acknowledge that humankinds’ influence on the environment can enhance natural climatic trends.
Next time you walk in Bird Park, or anywhere in Mt. Lebanon, try to visualize the stark tundra landscape here 15,000 years ago and the Mammoths roaming hills. Then, visualize Palm trees lining Washington Road sometime in the (not so) distant future. It could happen.
Neat web site: http://www.dcnr.state.pa.us/topogeo/parkguides/pg4_9/mmpgintr.htm .