15 Facts About Geologic Time That Made Our Brains Hurt

Species of woolly mammoths lived in North America, Europe, and Asia as far back as 300,000 years ago (if not before). By about 11,000 years ago, the number of mammoths on Earth had declined significantly, with only a few remaining in areas like Alaska, continental Siberia, and Wrangel Island in the Arctic.

Most woolly mammoths died off about 10,000 years ago, but the Arctic group lived into the Egyptian Middle Kingdom, c. 2040-1786 BC. It was during the Old Kingdom, c. 2686-2181 BC, that the grandest of the pyramids were built. These include noteworthy structures like the Great Pyramid at Giza, constructed for Khufu (r. 2559-2566 BC).

Roughly 232 million years ago, the Earth underwent a series of volcanic eruptions and climate changes that caused the extinction of one-third of all marine species - plus a number of animals that lived on land. 

Prior to this event, the supercontinent of Pangaea was a hot, dry place. Clouds could not move beyond coastal regions, and there were few mountains to break up the low-lying land. When the climate shifted, many animals were unable to cope with the wet, humid world. This wet period, known as the Carnian Pluvial Episode, lasted between 1 million and 2 million years.

Rainfall during the Carnian was not continuous, but areas like modern-day Utah experienced an estimated 55 inches of rain annually - as much as a temperate rainforest in the current era. This increase in rainfall occurred across Pangaea, causing "mountain-flattening mega-monsoons" and permanent changes to the supercontinent's terrain. 

Experts believe this massive geologic change allowed the dinosaurs to become the dominant lifeform on the planet, and led to species' increased diversification in the Late Triassic.

Not to be confused with cubic zirconia, a synthesized alternative to diamonds, zircon is a naturally-occuring mineral (the transparent variety is considered a semi-precious gemstone). A zircon crystal discovered in Australia is currently the oldest known fragment of early Earth - about 4.375 billion years old. 

That means the crystal was formed roughly 165 million years after the Earth coalesced from a cloud of dust into the planet we call home. That's a significant timespan to a human being, but the blink of an eye on a geologic scale. 

According to geochemist John Valley, the trace elements discovered in this zircon reveal that early Earth "wasn't an inhospitable place" and "was more like the Earth we know today."

Fossil evidence indicates the earliest living animals on Earth were those with shells. Species such as horseshoe crabs can be traced to 450 million years ago, which means they outlived all of the dinosaurs twice over. 

While horseshoe crabs have survived at least five mass extinctions, they're not the oldest living organism on the planet. In early 2020, researchers discovered green algae that existed a billion years ago. The fossilized seaweed, Proterocladus antiquus, is believed to be one of the ancestors of land plants on Earth. There's also red algae from Canada and India that date to 1.2 and 1.6 billion years ago, respectively.

The Tyrannosaurus rex, a carnivorous creature whose name means "king of the tyrant lizards," might be one of the best-known dinosaurs in the world. T. rex, for short, stood as high as 40 feet tall and could weigh as much as nine tons, according to archaeological evidence. T. rex dominated North America during the Cretaceous period, about 65 million years ago.

Another commonly known dinosaur, the Stegosaurus, was an herbivore with a deadly, spiked tail that also lived in North America. Stegosaurus could be found during the late Jurassic period, about 150 million years ago. While it's common to see both T. rex and Stegosaurus together in popular culture representations of dinosaurs (like in movies from the Jurassic Park franchise), they actually existed as many as 80 million years removed from one another.

This also means that T. rex lived closer to when humans were around than Stegosaurus.

Scientists know the moon was volcanically active between 3.5 billion and 1 billion years ago, but images taken by the LRO spacecraft suggest volcanic activity continued long after that. In fact, three volcanic deposits are believed to be less than 100 million years old, and one might be less than 50 million years old. 

The age of the dinosaurs, or Mesozoic Era, lasted between 245 million and 66 million years ago, which means volcanoes may have been erupting on the lunar surface during this time. As Space writes, "If only dinosaurs had invented telescopes, they might have seen lava occasionally oozing from the surface of the moon."