The Great Flood

I’ve been thinking off-and-on for a while now about Milankovitch Cycles and the fact that Earth is now overdue for a return to an ice age. It helps that my Mother lives in an area that has been very cold recently and which, thousands of years ago, would have been covered by the southward expansion of the Laurentide Ice Sheet.

One curious aspect of glaciers are the rocky deposits that are left by them, which are called moraines. It turns out that, in areas on Earth which were once covered by glaciers, moraines are a dominant factor of the landscape.

I’m also lucky because I live in an area not too far from where there exist glaciers here in the US, since they no longer exist in many areas. There are none in the entire Eastern half of the US. One day I really would like to spend some time and visit glaciers and explore them.

In one of the articles I was reading about the ice age history of the part of the country I came from, there was a picture of a mastodon that had been excavated over a century ago and is now in a museum.

I actually never really read much about mastodons. One hears more often about mammoths in the news when, every now and then, a carcass happens to be found somewhere in Siberia when permafrost melts. I know that the remains of some mammoths were sufficiently preserved to allow analysis of DNA.

I started reading about mastodons and immediately there was mention of the Quaternary extinction event. What is it that caused around 33 of 45 genera of large mammals in North America, and significant numbers elsewhere around the globe, to become extinct?

One proposed hypothesis is that it was due to the impact of an asteroid or meteor. This lead me to read through references from the Wikipedia article and eventually find another post, “Seven for the Seven Stars in the Sky“, which has a fascinating explanation of the effects of the impact of a large bolide on Earth:

The geologist, Professor Robert Schoch PhD, in his book, Voices of the Rocks, says:

”Whether an asteroid or a comet, the Tunguska bolide was hardly an oversized space object … Thousands of comets and asteroids of much larger dimensions come close enough to Earth to pose a threat of collision. What would happen if one of them hit?

For example, let’s look at the hypothesized effect of an impact with a good sized rocky asteroid – one a little over six miles in diameter traveling at 55,000 miles an hour …

The atmospheric effects of the impact would affect an entire hemisphere within minutes. Assuming 10% of energy of the impact went into the blast wave, wind velocity at the epicentre would hit close to 1,500 miles an hour, about a dozen times faster than the most powerful hurricane or typhoon … nothing short of a mountain could stand up to such a tempest. Nor could it bear the heat. At the same distance from the blast centre, the air temperature would increase by more than 850 degrees Fahrenheit, incinerating buildings, melting roadways and crisping human bodies to crematorium ash.” (3)

The post continues:

Schoch goes on to list other effects of impact with an extraterrestial object – things like chemical changes to the atmosphere caused by the heat generated in its flight through: formation of acid which would fall as rain, partial destruction of the ozone layer and increased carbon 14 (making carbon dating wildly inaccurate) etc. (4)

However, these effects are temporary and short lived. Longer term and, as far as animal life are concerned, far reaching effects follow from whether the impact site is on land or in the sea. He draws attention to computer simulations which show that the height at the shoreline of a tidal wave (tsunami) caused by an impact in the ocean is dependent on the depth of the sea at the impact site. In other words, if the bolide hits the earth at the site of an ocean trench five miles deep, the tsunami will be five miles high when it strikes the coast. Salt water will wash over everything, rushing far inland and will cover land based glaciers with the same effect as salting an icy garden path. The heat generated on impact will vapourise huge amounts of water, and water vapour is a greenhouse gas, so raising temperatures to help to keep the melting ice from refreezing. As Professor Schoch says:

”… a large amount of seawater would evaporate in the heat and would escape into the atmosphere as torrential rain clouds, which would be carried around the globe. A flood, again of global proportions would be the likely result.” (5)

By comparison, the tsunami that resulted from the 2011 Tōhoku earthquake generated waves that reached a maximum height of around 40 meters and which reached a maximum inland extent of 6 kilometers. The effect of a five mile high tsunami due to a bolide impact in the ocean would be unimaginably vast and very well could be something that would wipe out many species.