London: Spin a globe and what land you see among the vast blue swirl of our planet is the consequence of millions of years of geological battle. Plate tectonics has created mountains and valleys, plains and rifts – the land on which we and our fellow terrestrial species must live.
Incredibly, we’ve only really understood this process for the past 50 years, and it’s during that time that we humans have been doing our own Earth-shaping. We are moving mountains through mining and other extractions, for example, and global warming (owing to the carbon we’re releasing from fossil fuels) is causing low-lying islands and coasts to drown under sea level rise. Global warming is having a truly global impact: melting of ice in Antarctica and Greenland is squashing the planet – the Earth is less round because of us.
Plate tectonics has a big effect on life on Earth. As islands emerge through volcanic eruptions or other uplift, land becomes available for animals and plants to colonise, and over millions of years, they evolve distinct characteristics – they become new species. They same thing happens if populations become separated from each other through other land separations, for example, when plate tectonics engineered the split of Africa from Antarctica, or when South America split from Antarctica.
On a rare occasion, the opposite happens. When the continents of South and North America crashed into each other, their separate ecosystems also interacted. Species that had evolved in isolation from each other suddenly had to compete and it can’t have been pretty. We have evidence of the battle in the fossil record of extinctions and spreading habitats.
When we were in Panama, we visited some of the palaeontology digs in this vital corridorbetween the two continents with Carlos Jaramillo, a geologist at STRI. Carlos showed us some of his extraordinary discoveries, including ‘Titanoboa’ (the world’s largest snake) and some teeny tiny horses just 20 centimetres high.
Carlos is reexamining the date of the continental collision – the date for the closure of the Great Central American Seaway – and he’s found evidence that they may have crashed into each other nearly 20 million years earlier than we thought. The new date is not only interesting for geologists, it has repercussions for climate predictions. I wrote about it in New Scientist this week.
Around a century ago, we humans re-split the continents when we built the Panama canal. In perhaps the first example of a major engineering project assessing an environmental impacts assessment, the US government asked scientists from the Smithsonian Institute to investigate what might happen if the Pacific and Atlantic Oceans were reconnected. The environmentalists were concerned that merging species that had been separated for millions of years, from corals to fish, would lead to extinctions and ecosystem collapse.
In order to prevent this, the canal steps up in elevation from each coast to a central lake. Freshwater flows from the lake down the canal to the oceans. Despite these efforts, there is still some species transfer, even if it is far less than it might have been.
Recently, humans have outdone plate tectonics on the species-mixing and extinction front. We’ve introduced animals and plants to almost every one of the planet’s ecosystem from the Galapagos (as I described in an article in Science) to Antarctica. Invasive species are now so widespread that ecologists are changing tack on their conservation strategy. They are beginning to look anew at these hybrid, or ‘novel’, biomes to see what value they bring to the ecosystem. A group of 18 ecologists have written a commentary in Nature this week explaining this shift in direction.