This forest was buried standing up. It took one eruption. More than twelve feet of ash came down, and the biggest trunks never fell. They are still upright today, turned to stone, under a city in Germany. And their rings may have recorded the Sun.
This is the middle of the giant continent Pangaea, a little north of the equator. Most of the land around here is a dry, red plain. But in this one low spot, the ground stays wet all year. So a forest grows here, dense and green. Tree ferns. Seed ferns. Tall woody trees related to conifers. And giant horsetails at least fifty feet high, cousins of the knee-high ones alive today.
The forest is full of animals too. Small, lizard-shaped climbers, about sixteen inches long, cling to the trunks. Scorpions about five inches long sit in burrows between the roots. Snails crawl through the soil beside them.
To the east, there is a volcano. One day a little ash drifts over the forest and settles. Nothing else happens. Roots even begin to grow into it. So weeks pass, maybe months.
Then magma meets wet ground, and the volcano explodes. First comes ash. It is fine, wet, and not even hot. It falls like gray snow, and it strips the leaves from the trees. The little climbers probably drop from the branches into it. The scorpions are sealed in their burrows.
The eruption gets stronger. Twigs come down, then branches, then whole treetops. Then the cloud over the volcano collapses. It pours across the ground as a hot avalanche of ash and pumice. It snaps the smaller trees about five feet above the soil. It throws them down with their tops pointing away from the volcano. But the thickest trunks hold. And the ash keeps piling up around them, deeper than a room is tall.
So how long did it take? Nobody can time it to the hour. But from the first heavy ash to the last, there is no gap. No soil. No new roots. It was one eruption, start to finish.
Underground, the wood turned to stone. Much later, a city grew on top of it. Its name is Chemnitz. People there have been pulling stone trunks out of the ground since the seventeen hundreds.
In two thousand and eight, the city's natural history museum dug into a lot that had never been built on. The pit was about the size of a basketball court. In it stood fifty-three trunks, still rooted in the soil they grew in.
And the stone had kept more than their shape. It had kept their rings. So two scientists measured them, in wood from the pit and from the museum's shelves. About two thousand rings in all. One trunk alone held seventy-seven.
A tree here added one ring a year. The team takes a wide ring to mean a wet year, and a narrow ring a dry one. And these trees all died together. So their last rings are the same year. That let the team line most of them up, ring for ring, back through the forest's last seventy-nine years.
The rings did not change at random. They swelled and thinned together, in a beat. Wide, then narrow, then wide again, about every ten and a half years.
What could make a whole forest grow in step? Something else keeps that beat. Dark spots cross the face of the Sun, and they come and go about every eleven years. Over the last four centuries, that cycle has run between about ten and a half and eleven years. The forest's beat sits inside that range. So the two scientists think these trees felt the Sun. Its cycle nudged the rains, and the rains set the rings. By their own word, that last step is speculation.
That is a match, not a proof. Other things can run on a ten-year beat. Insect outbreaks can. So can swings in the weather that have nothing to do with the Sun. And six beats is not many. Some tree-ring scientists are not convinced.
But the beat itself is there, in trunk after trunk. And if the reading holds, the Sun was keeping the same time then that it keeps now.
One eruption buried this forest standing up. It also stopped every tree on the same ring. That is why those rings still line up today.
