Hundreds of millions of years ago, the first plants began spreading across Earth’s land. This major turning point helped transform the planet into the world we know today.
But new research suggests that the rise of early land plants may also have had a darker side: they might have contributed to two of Earth’s ancient mass extinctions in the oceans.
Professor Thomas Algeo from the University of Cincinnati College of Arts and Sciences has spent years studying the five major mass extinctions in Earth’s history.
In a recent paper published in Nature Ecology & Evolution, he provided context for a new study that looks at how plants first colonized land—a process scientists call terrestrialization.
A research team led by Jiachen Cai analyzed chemical records of carbon and phosphorus preserved in ancient rocks. Their findings suggest that the earliest land plants spread rapidly across continents about 460 to 450 million years ago.
The arrival of plants on land dramatically reshaped Earth’s environment.
As plants spread, they helped increase oxygen in the atmosphere and released nutrients into rivers and oceans. In many ways, this transformation helped make the planet more suitable for complex life.
But these changes may also have had unexpected consequences for marine ecosystems.
The researchers believe early plants might have first appeared on an ancient continent called Laurentia before spreading to other landmasses, including the enormous supercontinent Gondwana. Gondwana once covered a vast area stretching from near the South Pole to regions close to the equator.
Fossil evidence suggests that primitive plants—possibly mosses, liverworts, or early vascular plants—began to spread widely during this period. However, scientists still do not know exactly which types of plants dominated the earliest landscapes.
Around 445 million years ago, during the Late Ordovician, Earth experienced one of its major mass extinctions. Rising plant populations may have altered the chemistry of the oceans by releasing nutrients from weathered rocks into waterways. These nutrients could have disrupted marine ecosystems.
A similar process may have occurred later during the Devonian Period. About 372 million years ago, another mass extinction wiped out roughly 70 percent of marine species.
Some scientists think this event was linked to the spread of more advanced plants with roots and vascular systems. These plants may have pumped large amounts of nutrients into the oceans. This could have triggered massive algal blooms—sometimes called red tides—that depleted oxygen in the water and harmed marine life.
However, the cause of this extinction is still debated. Another theory suggests that huge volcanic eruptions created massive rock formations known as large igneous provinces. Weathering of these rocks could have removed greenhouse gases from the atmosphere, causing global cooling.
Scientists agree that climate cooling played a major role in the Devonian extinction. What remains uncertain is what triggered that cooling in the first place.
Today, researchers can observe similar processes in small ways when plants begin colonizing new volcanic islands such as Surtsey near Iceland or in the Galápagos Islands. Seeds arriving on barren land gradually break down rock, form soil, and create ecosystems—a process that can take centuries but happens very quickly on a geological timescale.
By studying these modern examples and ancient rock records, scientists hope to better understand how the earliest plants reshaped Earth—and whether their rise may have unintentionally helped trigger dramatic changes in life in the oceans.
Source: KSR.
