Earth: 360 Million – 250 Years Ago

At the end of the last discussion, we established the hot, flourishing world of the Devonian period. During that time, we saw life completely transform. I also mentioned that there was an event that brought the world out of this hotter period, which allowed for yet another extinction event. During this post, we will start off with the event that ended the Devonian period, which was when the climate began growing cooler. Eventually, we will make our way to the near-present day conditions.

The Paleozoic Ice Age: 360-260 Million Years Ago 

So, how did Earth get itself into another ice age? Well, there are multiple theories. One of these theories continues on the fact that the Devonian period was full of plant life, ranging from small ferns to massive trees. When this vegetation expanded, they took in carbon dioxide from the once-hot atmosphere, causing concentrations to reduce toward the end of the Devonian, or in this case, the beginning of the Paleozoic glaciations. Other theories do exist

However, during the periods when glaciations were less extent, life continued to evolve and thrive. An example of this would be the Carboniferous period, which featured a more tropical climate. When dead trees fell, new ones grew, but the dead plants would not completely decay. Once the seas rose, pressure and heat would cause this plant material and the carbon trapped within them, to become the coal beds of today. 

After about 100 million years of the Paleozoic ice age, the ice sheets began receding again. 

(See how life diversified during the Carboniferous period) 

The Great Extinction: 252 Million Years Ago  

Representing the end of the Paleozoic age and known as “The Great Dying”, 95% of marine life and 70% of life on land was demolished by a supervolcano. This volcano spewed record greenhouse gases throughout Earth, causing dramatic changes to the oceans, landscape, atmosphere and life. As increased greenhouse gases from the volcanic activity continued to warm the planet, life bounced back greater than ever. 

Learn how scientists pinpointed the cause of the Great Dying.

Mesozoic Era: 252-66 million years ago 

More specifically, this begins the time when dinosaurs evolved and began roaming Earth. At the time, the continents were merged together, forming the more familiar supercontinent, Pangea. Evidence shows that as the continent split apart, hot temperatures continued, with conditions ranging from moist to dry, changing sea levels multiple times. It was during this warm era when many ancestors of today’s plants and animals took over the land and seas. Over the last 100 million years, global temperatures have peaked twice. (

The supercontinent, Pangea, began splitting toward present locations about 175 million years ago.

 Cretaceous Hot: 92 million years ago 

One of these temperature spikes occurred about 92 million years ago, known as the Cretaceous Hot Greenhouse. As the continents continued drifting apart, the ocean floor was completely changed. Underwater and surface volcanoes may have boosted atmospheric carbon dioxide during this time. Temperatures climbed so high that reptiles lived in the Canadian Arctic and forests thrived near the south pole.  

A study from 2015 shows that a short cooling period caused by a decrease in carbon dioxide concentrations happened toward the end of the Cretaceous Hot Greenhouse. While there is still no evidence of glaciation, temperatures at the tropics reduced from 81°F to 41°F. The final blow was caused by a different extreme event, which caused life to come to another screeching halt. Have you ever heard about the extinction that wiped out the dinosaurs? Well, here it lies, marking the end of the Mesozoic Era. 

The K-T Extinction: 66 million years ago  

At this time, an asteroid struck the Earth near what is now the Gulf of Mexico. The material thrown into the atmosphere consisted mainly of pulverized rock and vaporized sulfuric acid. This cloud of material covered the planet, reducing the amount of energy reaching the surface from the Sun and sending Earth toward a brief cooler period. After some time, scientists believe that carbon dioxide from the same blast lingered in the atmosphere, causing Earth to begin warming once again.

The asteroid was about 8 miles in diameter, traveling at about 27,000 miles per hour, and created a 124-mile-wide crater.

Cenozoic Era: 66 million years ago – Present Day 

After about 70% of life on land was wiped out, it marked the beginning of a new era, the Cenozoic, which happens to be the current era we are living in right now. The second and final peak of temperatures occurred during this period, with the concluding end of the Cenozoic being characterized by ice age events. For now, let’s view the “most recent” time Earth experienced global warming. 

Paleocene Eocene Thermal Maximum (PETM): 55 million years ago 

When I say “most recent”, I mean about 55 million years ago. Earth wasn’t at its hottest, but global temperatures averaged 73°F as a large amount of either carbon dioxide or methane was released into the atmosphere through an unknown series of events. Scientists considered volcanic activity, thawing permafrost, methane from ocean sediments, wildfires, and even a comet . As a result, the PETM saw some of the more extreme swings in climate over a relatively short amount of time. Perhaps, within a period as little as 20,000 years ( was a huge diversification of life in the surface waters and on land. Crocodiles and palm trees were living above the Arctic Circle. Deep ocean life was destroyed by ocean acidification. We’ll talk more about the significance of the PETM later. 

This palm fossil was found in Wyoming (
Deep ocean temperature data taken from ocean sediments show a warm spike about 55 million years ago.

For most of the Cenozoic Era, temperatures remained warmer than today, up until about 14 million years ago, when Antarctica began producing its ice at a large scale. The formation of the Himalayan mountains may have pulled carbon out of the atmosphere by weathering rock, and a change of ocean currents caused by tectonic activity may have also assisted the ice formation. The stage was set for Earth’s final ice age, which is still ongoing. 

Tectonic forces separated Antarctica from South America, forming Drake’s Passage, forming a cool current around Antarctica, allowing ice to extend.

The Quaternary Ice Age: 2.6 Million Years Ago – Present Day 

Did you catch that? Present day? Does this mean we are currently living in an ice age? Yes! Currently, we are living in a mild interglacial of the Quaternary ice age. Actually, there were many times during this ice age, when glaciers advanced and retreated. If you remember, these periods of glaciation/deglaciation occur within ice ages, and these are known as glacial and interglacial periods. Up until about 800,000 years ago, these periods ran on cycles of 41,000 years, when suddenly, they began occurring every 100,000 years for reasons still unknown to the science community.  

These changes in climate were caused by changes in Earth’s orbit, tilt, and wobble, formally known as the Milankovitch cycles. The last of the glaciations caused by this cycle occurred 110 million years ago. This final glaciation of the Quaternary ice age appeared to have left its mark on the Neanderthals, a human species, around 20,000 years ago. Obviously, Homo Sapiens, or us humans, evolved and survived the expansion of the ice. 

During the last glacial maximum, ice extended as far south as Kansas!

12,000 Years Ago: Our Interglacial 

After the ice reached as far southward as it could, eventually a tipping point was reached and the ice began receding all the way back to where it continues receding today. As the ice began receding, the surviving Homo Sapiens turned to farming for survival, and thus, finally began the rise of human civilization some 10,000-7,000 years ago.

Let’s just say that the climate remained relatively stable up until about 250 years ago, when the United States was first founded, and the world entered a time that, I like to say, changed the ballgame.

The Industrial Revolution… 

I would also like to point out that, at this point in my posts, human life has had zero influence on the climate, simply because we did not exist until about 20,000 years ago. Even still, nothing has changed the planet like we have managed to do, over a period of just 250 years.

See how humans have managed to speed up Earth’s natural climate processes in the next post…

-Andrew Bower

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