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Lessons from a Black Hole.

The M87 black hole image shows it as it looked 55 million years ago. What did Earth look like back then? It was undergoing the PETM... which was a big mess!

Over a 5 day period in 2017 the skies were clear enough at 8 radio telescope sites across Earth to record unprecedented data at the center of a giant galaxy. Over the next few years, the EHT collaboration painstakingly processed this data and created what will be considered one of the greatest astronomy images in history, a black hole.

This black hole resides at the center of the enormous elliptical galaxy called M87 which is roughly 55 million light years away (give or take 2 million light years). This means light emitted from the edge of the event horizon took around 55 million years to reach Earth! In other words, the image we are looking at now is actually from 55 million years ago. Folks, pay attention, because this is the closest to time travel we are going to get! Being paleontology minded, I quickly asked the question, what did the Earth look like when the black hole posed for this photo?

The short answer is the Earth was a big mess; it was undergoing an anomaly... a hiccup of sorts... there wasn't a large mass extinction, but this anomaly was dramatic enough to end a geologic Epoch. Sometime between 56 and 55 million years ago Earth was being ravaged by extreme floods followed by extreme droughts and massive wildfires. The oceans acidified, dissolving the shells of mollusks and shelled plankton! Mammals shrunk in size. Then, two smaller but similar events took place over the next 3 million years! Let's look into this in more detail.

At only 11 million years after the great Cretaceous-Paleogene mass extinction (that asteroid impact thing), most people would assume Earth was continuing to make a comeback. Dinosaurs were now fossilized. Mammals had risen and diversified to take over the open ecological niches. Everything was fine. Then, right when stellar food began to fall into the accretion disk that would come the famous black hole image, Earth underwent an "anomaly" or as paleontologists like to say, an "event". This short lived event, called the Paleocene-Eocene Thermal Maximum (PETM), took place between 56 and 55 million years ago. Subsequent, smaller events continued to take place until 52 million years ago.

What was the PETM

The PETM is the largest and most dramatic spike in global atmospheric carbon levels and temperatures in Earth's history. If you had someone hand plot a graph of the CO2 in the Paleocene and Eocene, you would assume they sneezed and their hand flew off the paper right at the PETM data point. On a geological time scale, this spike happened over a very fast 20,000 year timeframe but had dramatic consequences to life on Earth. It also took around 100,000 for the climate to go back into equilibrium from this carbon injection.

What caused the PETM

The PETM and the subsequent smaller spikes are thought to have originated from volcanism on the ocean floor along the Mid-Atlantic Ridge. The Atlantic Ocean was widening at a fast rate as preserved basalt deposits show numerous volcanic eruptions taking place along the Mid-Atlantic Ridge. The wide scale volcanism itself didn't cause the atmospheric carbon spike. It's thought the volcanism caused large deposits of methane hydrates on the sea floor to be released. These hydrates combined with oxygen to produce CO2. The large infusion of CO2 in the atmosphere warmed the Earth and created feedback loops. The rising temperatures melted the arctic permafrost peats which in turn released more greenhouse gasses. The peats may then have dried out and caught fire. The widespread peat fires further added to the CO2. There is also research suggesting a coincidental impact event at the onset of the PETM. Some mechanisms for the carbon injection are still under debate, but, regardless of how it got there, it's thought that around 6.8 trillion tons of carbon was released into the atmosphere (Panchuk et al., 2008).

What effects did the PETM have on life?

The ocean naturally absorbs CO2 from the atmosphere, and the spike in atmospheric CO2 therefore caused a spike in ocean CO2 concentrations. This changed the pH of the water, causing it to turn acidic. The acid dissolved many organisms with calcium carbonate shells. Various mollusks and shelled planktons went extinct. Entire coral reefs bleached and died.

The massive carbon release caused the already ice-free Earth to warm up even more. This put Earth's climate into chaos. Fossils indicate major changes in plants and animals. The arctic areas became subtropical and many plants and animals that normally lived near the equator migrated into much higher latitudes. This trend can be seen in many places on Earth including New Zealand and Greenland. A notable example is the Big Horn Basin in Wyoming where Scott Wigg and Ellen Currano studied plants before, during, and after the PETM. They found a sharp decline in temperate plants and an immigration of dry tropical forms at the start of the PETM (Scott and Currano, 2013). Fossil and paleo sedimentation evidence also shows numerous mudslides coupled with intense and widespread forest fires (Fung et al., 2019). It appears weather became severe, repeatedly swinging from extreme droughts to extreme rains.

As far as land animals, mammals in particular shrunk to cope with the rising temperatures and chaotic climate. One of the more studied examples is the horse. Horses first appear just before the PETM. They were about the size of a modern day dog. During the PETM, horses shrank by a factor of 30% (Secord et al., 2012) to the size of house cats. Right after the PETM they start to grow in size again. Although there were no mass extinctions of mammals, the PETM caused a disruption and abrupt shift in mammal evolution; many of today's mammal orders emerged right after the PETM, including the first primates and whales.

What does the black hole image tells us about our present and future?

As we look at that black hole picture from 55 million years ago, we can now imagine what Earth was also like at that time. It was undergoing the most extreme climate swing in history. The PETM, followed by 2 smaller events, was triggered by enormous carbon injections into the atmosphere which turned the climate into chaos, caused marine extinctions, and abruptly shifted the evolution of mammals.

It's ironic, as we look at the black hole photo today, the same thing is happening again. Today we are pumping more carbon into the atmosphere per year than any year of the PETM event. We had a chance to stop it, but it's now most likely too late. Maybe when looking into the black hole, it should serve as a reminder of the terrible things that happened in the past and a warning of the terrible things to come.

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References

Fung, M.K., Schaller, M.F., Hoff, C.M., Katz, M.E., and Wright, J.D. (2019). Widespread and intense wildfires at the Paleocene-Eocene boundary. Geochem. Persp. Let. 10, 1-6.

Panchuk, K., A. Ridgwell, and L. R. Kump (2008). Sedimentary response to Paleocene-Eocene Thermal Maximum carbon release: A model-data comparison, Geology, 36(4), 315-318.

Secord,R., Bloch,J.I., Chester ,S.G.B., Boyer ,D.M., Wood ,A.R., Wing, S. L., Kraus,M.J., McInerney ,F.A. and Krigbaum, J. (2012). Evolution of the earliest horses driven by climate change in the paleocene-eocene thermal maximum. Science 335, 959 - 962.

Svensen, H. (2012). Bubbles From The Deep. Nature 483, 413-415. DOI: 10.1038/483413a

Wing, Scott and Currano, Ellen. (2013). Plant response to a global greenhouse event 56 million years ago. American journal of botany. 100. DOI: 10.3732/ajb.1200554

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Recommended Books:

The Princeton Field Guide to Prehistoric Mammals
by Donald R. Prothero

This is a good book for an introduction to mammal evolution. Full of illustrations, it gives a great overview of perhistoric mammals from after the extinction of the dinosaurs, the Paleocene, into the Ice Ages. Immerse yourself in the lost world of these prehistoric beasts. Available in hard cover or Kindle.

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Horned Armadillos and Rafting Monkeys: The Fascinating Fossil Mammals of South America
By Darin A. Croft

During the Cenezoic, South America was home to some of the oddest mammals of all time. This book emphesizes specific fossil sites in South America and walks through what the site was like in the past. Unlike some over technical books, this book keeps the reader completely enthused while bringing the past animals back to life. It includes 75 life reconstructions and many photographs of fossil specimens and the fossil sites. The Kindle version is discounted.

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The Rise of Mammals
Childrens Book by Matthew Rake

This Childrens book is a great introduction to mammals from the Paleocene into the Ice Age. If you child is a dinosaur lover, expand his horizon by showing them these fantastic beasts that ruled the Earth long after the Dinosaurs! It's available in an inexpensive print edition or a very discounted Kindle edition.

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