How Fossils Are Dated: Rock Layers, Ash Beds and Isotopes
A dinosaur bone carries no date stamp. Geologists read the layers around it and the slow ticking of uranium and potassium in volcanic ash to work out its age.
Category: Ancient World
Archaeology, fossils, dinosaurs and human origins: new finds, how scientists date them and what they tell us about the past.
What Was the Biggest Dinosaur Ever? Length, Weight and Debate
A thigh bone taller than a person, a cast too long for most museum halls and weight estimates that swing by tens of tonnes: how scientists size up the largest dinosaurs.
How Big Was Megalodon? New Size Estimates and Why They Changed
The biggest shark that ever lived is known mostly from teeth the size of a hand. Here is how scientists estimate its size, why the numbers keep changing, when it died out, and why it is not hiding in the deep sea.
How the Pyramids Were Built: Quarries, Ramps, Boats and Workers
A 4,500-year-old logbook, a ramp with post holes and a buried branch of the Nile have filled in how Egyptians built the Great Pyramid of Giza. Here is what the evidence says.
What Killed the Dinosaurs? The Asteroid Evidence Explained
A thin clay layer rich in iridium, a buried crater off Mexico and grains of shocked quartz: how scientists tied the end of the dinosaurs to one very bad day.
How Carbon Dating Works and Why It Stops at About 50,000 Years
Every plant and animal takes in a trace of radioactive carbon while it lives and stops when it dies. Here is how scientists turn that slow decay into a date, what can and cannot be dated, and why tree rings keep the clock honest.
Who Were the Neanderthals? Where They Lived and Why They Vanished
Stocky, big-brained and well adapted to the Ice Age, Neanderthals made tools, controlled fire and buried their dead. Part of them survives in our genomes.
How Old Is Stonehenge? Building Stages, Stone Sources and Purpose
Stonehenge was built and rebuilt over roughly 1,500 years, with stones hauled from Wiltshire, Wales and, it now appears, northern Scotland. Here is the timeline and what the evidence says it was for.