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Today, the Isthmus of Panama separates North America and South America. An isthmus is a narrow piece of land with water on either side. Nearly 20 million years ago, the Isthmus of Panama did not exist. Ocean covered the area where the isthmus is today. With a gap between North America and South America, the ocean waters from the Atlantic and Pacific could flow freely between. The organisms that lived in these waters could also move about freely between.

Millions of years ago, pieces of Earth's crust called plates began slowly colliding into each other. One plate, the Pacific Plate, was sliding under another called the Caribbean Plate. This caused a large amount of pressure and heat, making underwater volcanoes. Some of these grew so tall they became islands around 15 million years ago.

More volcanoes formed over millions of years, and some parts of the ocean floor got pushed up above water. Strong currents carried lots of sand, soil, and mud away from North and South America, making new islands.

About 3 million years ago, all this sediment created a narrow piece of land connecting North and South America, called an isthmus. Like a bridge made of land between the two continents, the isthmus split up species of organisms, making them different over time.

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Scientists believe the formation of the Isthmus of Panama is one of the most important geologic events to happen on Earth in the last 60 million years.

Even though it is only a tiny piece of land (relative to the sizes of continents) the Isthmus of Panama had an enormous impact on Earth’s climate and environment (including the species of organisms).

Before it existed, warm ocean currents could freely flow between the Atlantic and Pacific Oceans. But once the isthmus formed, it blocked this flow. This change affected the climate in a few ways.

First, it created a barrier that stopped warm water from moving between the oceans, which made the Atlantic Ocean warmer and saltier, while the Pacific Ocean became cooler.

The change in ocean temperatures influenced local weather patterns. For example, it likely affected rainfall patterns, winds, and temperature distributions around the isthmus and nearby regions.

Furthermore, the isthmus acted as a barrier to the movement of plants and animals between North and South America. This led to the development of distinct ecosystems on each continent. Animals and plants adapted to their specific environments, which increased biodiversity.

Overall, the formation of the Isthmus of Panama played a crucial role in shaping the local climate and environment, affecting ocean currents, rainfall patterns, and the distribution of species in the Americas.

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The Isthmus of Panama divides the Caribbean Sea and Pacific Ocean. During this part of his trip, Darwin observed species of snapping shrimp along the coast of the isthmus. Darwin noticed differences among them and concluded that these shrimp were different because of the phenomenon called speciation. Speciation is the process of new species arising from a single, existing species after being physically or geographically separated. In this case, the isthmus separated the snapping shrimp leading to differences over time. Darwin's observations here laid the groundwork for further research on biodiversity.

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The image shows 4 of 6 species of snapping shrimp known to have diverged due to speciation after the formation of the Isthmus of Panama. 

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When the Isthmus of Panama formed about 3 million years ago, it separated the snapping shrimp populations on the Atlantic and Pacific Oceans. Over time, these shrimp started to adapt differently because their environments changed.

The Atlantic and Pacific Oceans have different temperatures, currents, and habitats. This meant that the shrimp on each side of the isthmus had to adapt to their own unique conditions.

As a result, over millions of years, the snapping shrimp on the Atlantic and Pacific sides of the isthmus became distinct from each other. They developed different features and behaviors to help them survive in their particular habitat. This process of species forming differently from a single ancestor is called speciation.

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Geographic barriers, such as the Isthmus of Panama, are a factor that contributes to speciation. Other examples of geographic barriers are dams and land masses, such as canyons, mountains, or islands. These barriers physically separate a species causing differences among them over time.

In addition to geographic barriers, predators, changes in food supply, changes in climate (water temperature and currents) can also affect speciation.