Skip to content

Eyes Made of Crystal? - Trilobites are Bizarre

2017-06-30 · explainer · Hank · 3:39 · watch on YouTube

Topic: Science & nature (also: Projects) · mode: Explainer · tags: self promotion

Launching Eons, a new PBS Digital Studios show about the history of life on Earth, Hank explains why trilobites are bizarre and successful: early arthropods that lasted 270 million years, whose fossils are mostly shed exoskeletons, and whose calcite-crystal eye lenses had shapes 17th-century astronomers later reinvented.

What is said

The parts of the video and what is said in each (★ — how much it matters to the video).

00:00:00 — Why look at the past: Eons, a new PBS Digital Studios show on the history of life

  • ★★ Hank says it is easy to forget that the present is one snapshot of a huge history of life on Earth, and that looking at the past is instructive and fascinating. — 00:00:05
  • ★★★ Hank and his team have teamed up with PBS Digital Studios on a new show, Eons, about the entire history of life on Earth; its first episode is on trilobites. — 00:00:22 · Eons

00:00:38 — Trilobites: Cambrian origins, first arthropods, 270 million years of success, fossils that are mostly molts

  • ★★ Trilobites emerged around 500 million years ago, in the Cambrian Explosion when life grew more complex, and were the first true arthropods. (hedged) — 00:00:42
  • ★★ Arthropods, the segmented exoskeleton-covered animals like spiders, butterflies, millipedes and crabs, now make up three quarters of the world's species. — 00:00:52
  • ★ Hank says horseshoe crabs share some family resemblance with trilobites and some species coexisted with them (the conclusion of the sentence is unclear). — 00:01:08
  • ★★★ The last trilobites went extinct around 250 million years ago, but they were extremely successful, lasting 270 million years. (hedged) — 00:01:16
  • ★★ By comparison, primates have existed for around 50 million years, so 'we have a lot of catching up to do'. (hedged) — 00:01:26
  • ★★ Trilobite fossils have been found on every continent and over 15,000 species described. — 00:01:31
  • ★★★ Most trilobite fossils are not dead animals but shed exoskeletons, since arthropods must molt to grow; they still let scientists date and identify species. — 00:01:41

00:02:13 — Trilobite eyes: calcite-crystal lenses shaped like Huygens's and Descartes's lens designs

  • ★★ Trilobites were probably so successful because of strong exoskeletons, jointed legs and, a big deal, the first complex eyes. (hedged) — 00:02:13
  • ★★★ Some trilobite eyes had thousands of individual lenses made of calcite: they grew crystals in their eyes. — 00:02:25
  • ★★ Unlike human lenses, which change shape to focus, rigid rock lenses cannot, and they distort unless given very specific shapes, a problem 17th-century astronomers faced. — 00:02:40
  • ★★★ In the 1600s Huygens and Descartes devised lens shapes fixing this; the trilobites Crozonaspis and Dalmanitina had matching eye-lens shapes, keeping near and far objects in focus with less distortion. — 00:02:55
  • ★★ Hank exclaims that it took humans 300 million years to catch up with trilobite evolution, and says he just loves it. (playful) — 00:03:20

00:03:25 — Eons' first episode at youtube.com/eons with Blake and Callie; sign-off

  • ★★★ Hank invites viewers to watch Eons' first episode at youtube.com/eons, where he, Blake and Callie will take them through the history of life on Earth. — 00:03:25 · Eons

In the description and comments

  • ★★ The description adds that people have collected trilobites for at least tens of thousands of years, as they appear in Native American burial mounds. — video description
  • ★ The description says a trilobite genus first found in China is named Han, after the dynasty, and its one species known from a single fossil is named Han Solo. — video description · China
  • ★★ The extinction event that wiped out the last trilobites, covered on Eons, wiped out 90% of the species on Earth. — video description · Eons

Threads in this video

Where the stories that moved here went next

Mentioned

Central: Eons · trilobite

Also: People: Christiaan Huygens · René Descartes

Concepts: arthropod · calcite · Cambrian explosion · Crozonaspis · Dalmanitina · horseshoe crab · moulting · primate

Only in the description or credits: Blake (staff, mentioned from 2012) · China · Han Solo · Kallie Moore · PBS Digital Studios

← Previous: UNBOXING · Next → Civil Twilight