Long before trees overtook the land, Earth was covered by giant mushrooms, according to a new study published in the journal Paleobiology.

Researchers from the Smithsonian National Museum of Natural History and the University of Maryland analyzed fossils dating back more than 400 million years and found evidence of towering mushrooms that stood nearly 30 feet tall.

The study suggests that during the early stages of Earth's history, when the planet was warmer and wetter, giant mushrooms may have been the dominant form of life on land.

"This is a new way of thinking about how life evolved on land," said Brandon Laforest, lead author of the study. "It's kind of mind-blowing to think that for millions of years, the landscape of Earth was covered in these towering mushrooms."

The giant mushrooms likely thrived in the warm, moist conditions of the Carboniferous period, which lasted from about 360 to 300 million years ago. At that time, there were no trees to compete with the mushrooms for resources, so they were able to grow to enormous sizes.

The researchers also found evidence of other fungi and primitive plants in the fossil record, suggesting that a diverse ecosystem existed during this time.

While the giant mushrooms may be long gone, their legacy lives on in the form of the mushrooms and other fungi that still exist today, playing important roles in ecosystems around the world.

The study highlights the importance of understanding the history of life on Earth, and how it has shaped the planet we know today.