My Little Pony

Climate Change. It’s a topic that’s been in the media recently for a number of reasons, namely because we’re experiencing it now. We know that because we have climate records going back to 800,000 years (possibly [1.5 million years]) from ice cores. The gases trapped in the ice are made up of the atmosphere that was around when the ice formed. The atoms that make up the gas, like oxygen, carbon, and hydrogen, have different values of positive and negative particles (different isotopes) that relate directly to the temperature the planet was at the time. That’s how we know what temperature the planet used to be and how we can plot the data and form predictions about what the future holds (spoiler alert: it’s gonna get hot). For more on that, watch the video at the bottom.

This graph shows carbon dioxide levels over time. The higher the level of carbon dioxide, the hotter the temperature. From NASA. Credit goes to Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.

A [paper] was published this week that analyzed these same isotopes from the past. The Earth has gotten hotter in the past. One of these times, called the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) lasted for 200,000 years and caused the Earth to rise 5°-8°C over 10,000 years. (Note: we’ve risen [0.7°C over 100 years, which is about 10 times faster] than the natural warming cycles the planet has experienced.)

Lots of information in this graph. Here’s the breakdown. Time, in millions of years, is on the bottom (the x-axis) with present day on the right at 0 million years ago. The abbreviations above the time are for the names of the period (Pal = Paleocene, Eo = Eocene). Along the right, the y-axis shows the amount of a particular isotope of oxygen that tells us temperature. The green line in the graph is the amount of that isotope over time, and gives us a sense of temperature. The higher the line is the hotter the temperature, and the lower the line is, the cooler the temperature. Right between the Paleocene and the Eocene, you can see the spike that indicates a sudden hot temperature. You can also see the cooling trend that lead to the ice ages (“Rapid Glacial Cycles”).

This new study examined a time after the PETM (about 2 million years later, at 53.7 million years ago), called the Eocene Thermal Maximum 2 (ETM2). The record of this time is pretty complete in the Big Horn Basin of Wyoming. The authors analyzed the temperature before, during, and after the ETM2 using the isotopes contained in the soil and in the teeth of an early horse, Arenahippus pernix, and a couple of other mammal species. They also calculated the body size of these animals using the size of the first molar. Molar size corresponds well to overall body size in mammals, so we can use the molar size to estimate body size when we only have teeth.

Arenahippus pernix at the Swedish Museum of Natural History. From Wikipedia.

The authors found that as temperature increased, the size of the horse shrank (from 7.7 kg to 6.6 kg). As temperature fell again after the ETM2, body size increased (from 6.6 kg to 7.9 kg). One of the reasons for this shrinkage is that it’s easier to cool off a smaller body than it is to cool off a larger body. If the environment is warming up, then being able to cool off faster is an advantage. Also, there may have been fewer nutrients available if droughts were happening, so the horses may not have been able to grow to their full size. The last reason could be related to how much rain was available. Less rain means less plants and less food for herbivores. Whatever the reason or combination of reasons, what we do know is that climate change, like what we’re seeing now, will affect mammals in ways we are still discovering.

Figure 3 (A and C) from the paper. The first two columns show the carbon isotope levels in the soil through time. The further the points move to the left, the hotter the climate was. The right column shows molar size in Arenahippus. Points to the left are smaller molars and points to the right are larger molars. The molars get smaller just as temperature is the hottest, and then grow again when the climate cools down.

Video on atmospheric carbon dioxide from the Earth System Research Laboratory at the National Oceanic and Atmospheric Administration. More sources can be made available on request.

The Island Mammoths and the Sea

This week we’re going to talk about an [article] that’s so new, it doesn’t even have page numbers yet. The purpose of this study was to find out why a population of mammoths on the island of Saint Paul, Alaska went extinct. But first, let’s talk about mammoths.

Mammoths were large elephants that were covered in thick fur. They are most closely related to Asian elephants. Mammoths had teeth adapted to grinding, similar to modern horses, for eating grass and other plants. The last mammoths went extinct about 4000 years ago (that’s 2000 BCE). To put that in perspective, the earliest Egyptian pyramids were built around 2600 BCE. The Egyptians were building pyramids while the last mammoths were still roaming the tundra. Let that sink in for a minute.

mammoth PBS

An artist rendition of a mammoth (from PBS).

The authors of this study traveled to Saint Paul, Alaska: a tiny island that’s over 450 km (280 miles) away from Alaska and the Aleutian Islands.

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A map showing the location of Saint Paul Island, Alaska (the red marker) (from Google).

They took sediment core samples from the deepest lake on the island, Lake Hill. What’s a sediment core, you might ask? A sediment core is a sample of sediment or dirt that is gathered by drilling a deep hole. As the drill comes back up it is filled with a sample, or core, of the sediment from that spot. Because sediment is deposited in layers over time, these cores contain information about what the conditions were like in that place over time.

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A photo of a sediment core from a lake (photo by N. Krug).

The authors tested the cores for the presence of DNA and three fungal spores. The fungi they tested for are types that eat animal poop, so their presence in the cores will tell us that there were animals in that spot. The authors also tested the cores for plants, tiny invertebrates, pollen, and isotopes (chemicals that tell us about the environment) to understand how the environment was changing over the last 10,000 years.

Using all of these data, the authors found out that:

  • The ice melting at the end of the Ice Age was raising sea level and causing Saint Paul island to shrink.
  • Fresh water on the island was disappearing because the rising sea level invaded ground water and lakes.
  • Mammoth activity around the lake destroyed the plants around the lake and caused more sediment to fall in to the water, filling the lake with sediment and causing the lake to disappear faster.
  • These mammoths probably died of thirst around 5600 years ago.

These conclusions bring up a point that we all need to pay attention to: as sea level rises, the amount of freshwater on islands will drop. That means many of the Pacific Island nations, among others, are immediately in danger from sea level rise, not only from shrinking space, but also from losing freshwater sources. As sea level continues to rise, we will have many concerns about resources and population. Those who say global climate change is a myth are choosing to ignore a global problem that is already affecting us.

Studying extinct animals, like this Mammoth population on Saint Paul Island, can help us understand how climate change will affect us in the years to come.