Tree rings are the most commonly remembered traces of time

Humans are the longest-lived mammals, but we still feel that life is short. Everything is drifting on the long river of time, but the length of the journey can range from being born in a morning to dying in a night, to living forever.

Tree rings are the most commonly remembered traces of time.

In temperate forests, trees grow rapidly in the spring when there is plenty of rain, producing spring wood with loose and shallow spacing; they grow slowly in the bleak autumn, producing autumn wood with a hard and dense texture. As spring goes and autumn comes, spring wood and autumn wood alternate, forming layers of annual rings.

But not all trees grow in the same rhythm of one growth ring per year. Tropical trees generally do not have growth rings because they grow at a constant speed throughout the year. Subtropical trees such as Masson pine and yew have two growing seasons a year, so they grow two layers of growth rings a year. Citrus trees even have three growth rings a year. If there are abnormal climate years such as summer drought, some trees may also have missing growth rings or "pseudo growth rings".

In 2006, British researchers fished out an Arctic clam (Arctica islandica) in Iceland that was 507 years old. As the shell grows, it leaves a circle of lines every year, just like the annual rings of a tree. The researchers named the Arctic clam "Ming", indicating that it was born in the Ming Dynasty of ancient China.

Arctic clams are living ocean history books. The oxygen isotopes deposited in the shells can reflect the temperature of the seawater at that time, and the "annual rings" indicate the period of shell growth. By studying clam shells of different ages, we can understand the impact of the greenhouse effect on seawater at different periods in history.

An Arctic clam with its cuticle peeled off | Manfred Heyde / wikimedia

Zhuangzi said: "Small knowledge is not as good as great knowledge, and small years are not as good as big years." Cicadas do not know that there are four seasons in a year, while big trees consider eight thousand years as one autumn. Although cicadas were ridiculed by Zhuangzi, some short-lived creatures have an amazing concept of time.

The silverside (Leuresthes tenuis) in the southern California waters follows a precise activity cycle during the breeding season, laying eggs every fourteen days. The special thing about the silverside is that it lays its eggs on the beach, so that it can avoid predators in the sea. They lay eggs on the days of the new moon and the full moon, when the moon has the greatest impact on the tide. The sea water is the highest at high tide, and when the silverside rushes to the beach, the tide will push them as far as possible.

In the half month after spawning, because the tide is not that strong, the eggs can develop slowly on the beach until the tide rises again, when the little fish hatch and ride the tide back to the sea.

Female fish that bury themselves to lay eggs | Loren Rodgers

The life span of a single coral polyp may be short, but the calcareous skeletons they leave behind can continue to "build" for thousands of years. Although age cannot be equated with wisdom, the traces of time left on life can always give us some valuable inspiration. Corals deposit a very thin layer of calcium carbonate every day, leaving a ring pattern, and the growth rate of corals varies in different seasons of the year. Therefore, corals are both calendars and almanacs. The amount of calcium layer can tell us the date, and the thickness of the calcium layer can help us identify the year.

Coral reefs, and the skeletons of different corals | Toby Hudson & Jon Zander & Narrissa Spies & James St. John / wikimedia; piqsels

The calendar on coral can also reveal some unexpected information. The Silurian coral fossils from more than 400 million years ago have 420 lines per year, which means that the Earth at that time had 420 days per year. From this, we know that the Earth's rotation speed has been slowing down due to the attraction of the moon.

Those tiny passers-by have thus recorded the greatest and longest-lasting changing force in the universe - gravity.

If we look at the entire river of time, human beings' years and years are just like the work of coral polyps, leaving only a thin line of sediment.

Can the marks we leave behind be connected to the vast universe?

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