Millions of Years of Climate Change

For several decades, global climate change has been a phrase the news media and others appear to love using. The idea isn’t too hard to grasp, and yet it can cause confusion. People might wonder how anyone can know the extent of the change, especially millions of years ago, before there were people to keep track of temperature and precipitation amounts as they fluctuated. Truth is that there are ways scientists use to show that climate change has been going on for a long time.

Rock core samples

Rocks are continually being formed on the earth. There are several processes by which this occurs, including by volcanic and sedimentary deposits. Sedimentary deposits are especially interesting to scientists studying the climate in various locations around the world. This is because sedimentary rocks usually form layer upon layer, trapping anything that happened to be alive at some point, between the layers.

By taking rock core samples, people can carefully uncover whatever organisms were laid down with the sediments that would eventually become rock. Though it may not sound like studying fossilized plant and animal remains would have much to do with studying the climate, the opposite is actually the case.

It is also interesting to note that in many locations, sedimentary rocks are even found at great altitude, such as on the tops of mountains. This shows that at one time, the mountain tops were under water, before the mountains formed. Due to this, rock core samples can be taken almost anywhere that there is rock, from the bottom of the ocean to the tops of mountains.


Some plants and animals only live in a narrow climate range. If they are found in the rock samples, these indicator species define the climate at the time the sediment was originally laid down. From this, scientists can paint a global climate picture. If rock cores taken in quite different locations have the same organisms, it indicates what the climate was over a very large area, and this can reach back many millions of years.

Ice cores

Similar to taking a rock core, scientists can also take ice cores. While the samples can’t be taken over as large an area, worldwide, ice samples are even better and more precise. Ice also traps atmospheric gasses, so the makeup of the air can also be determined at any point in time, when the ice existed. The greatest ice fields for this research is probably Antarctica, where the ice can be two miles deep in places. Antarctica is also a desert. Little precipitation falls, so a timeline is more compacted and easier to determine.

With ice, though, it is less a case of determining the micro organisms than it is in identifying pollen grains trapped in the ice, since most specimens that are trapped were airborne before they were caught. Still, these serve the same purpose. Even today, certain plants usually only release pollen when the temperatures are right for the species of plant. Identifying the plant, then, gives researchers an idea of what the climate was at a given time in the past.

There are other methods that are used to determine climate change through the years. However, from the data these methods have given, people know that about 2,000 years ago, the climate was hotter than it is today, though carbon dioxide levels were lower. People know that the carboniferous period, millions of years ago, was substantially hotter than it is today, and that the heat lasted for a great amount of time, over millions of years. 

Ultimately, it can be shown that the climate has been changing for millions of years or longer. There are many ways that people can use to determine this with near certainty. Judging from this information, it is likely that the climate will continue to change. After all, the earth is dynamic, not static.