Petrifi ed forests

ENVIRONMENT

“ As the floods washed or evaporated away, they left these quartz slabs scattered around the plains”

Petrified forests

Perfectly preserved 225-million-year-old trees

All over the world you can find strange-looking slabs of wood, strewn across a barren landscape. However, these haven’t actually been wooden for millions of years.

Around 225 million years ago, prehistoric trees fell into rivers, where they were quickly covered with a layer of sediment, silt and mud. This rapidly formed a tight wrap around the trunk, cutting off any oxygen that would have rotted the wood. Over time, minerals were absorbed into the wood, including silica. This material is known for its crystallising properties and as the log slowly rotted away over a period of many centuries, the silica replaced it, forming stunning crystal representations of the original material’s shape and turning the wooden logs into quartz slabs.

As the floods washed or evaporated away, they left these quartz slabs scattered around the plains. Wind and sand erosion continued to batter these slabs until the last few pieces of organic material was stripped away, leaving stunning quartz blocks dotted around barren, arid landscapes around the world.

Petrified wood tends to be found in areas near volcanoes. This is because the silica, which is key to the production of the stunning crystals, usually comes from ash spewed out by an erupting volcano. Most petrified forests are protected areas, so you are allowed to go and view these incredible natural phenomena, but unfortunately you can’t take any of it home for your mantelpiece.

Why do plants rot?

Once a plant dies, it will start to rot (decompose). They decay because microorganisms release enzymes that break down compounds for digestion. Bacteria and fungi – the main decomposers – depend on moisture and oxygen for their respiration. When both are absent from the process, the microorganisms work much slower and, in the case of petrified wood, rotting takes up to millions of years.

Notable petrified forests

The Petrified Forest National Park near Holbrook, Arizona, is one of the biggest and most impressive petrified forests in the world. It houses nearly a dozen different types of petrified wood, ranging from conifers to ferns. It grew to today’s impressive size due to the large river network upstream of the site.

The petrified forest near Maadi, around 30 kilometres (19 miles) from Cairo in Egypt is quite young, the logs appearing around 35 million years ago. This was a time of geological upheaval as the Red Sea formed from the separation of tectonic plates. The forest spans about six kilometres (four miles) and was declared a protectorate in 1989 so it could be officially preserved by the Egyptian government. Argentina’s Petrified Forest National Monument is a jaw-dropping demonstration of the changes the planet has undergone in its lifetime. Before the vast Andes mountain range even existed, vegetation was everywhere, some trees reaching 100m (328ft) high. Then, geological shift created the Andes and accompanying volcanoes, burying the plant life in ash, creating an amazing petrified forest.