Question 1

How do you say Phanerozoic?

Accepted Answer

Phanerozoic is pronounced FAN-er-oh-ZOH-ik. The tricky part is the silent P at the start, which comes from Greek and is common in scientific words. Break it into four beats: FAN, then er, then ZOH, then ik, and put the strongest emphasis on ZOH. Say it a few times fast and it starts to feel natural.

Question 2

What does Phanerozoic mean?

Accepted Answer

Phanerozoic comes from two Ancient Greek words: phaneros, meaning visible, and zoion, meaning animal. So it literally means the time of visible animals. It got this name because it is the eon when animals first evolved hard shells and bones that could be clearly preserved as fossils, making life suddenly visible in the rock record for scientists to study millions of years later.

Question 3

When did the Phanerozoic start?

Accepted Answer

The Phanerozoic began approximately 538.8 million years ago, with a precision of plus or minus 600,000 years. The official starting boundary is defined by the first appearance of a distinctive trace fossil called Treptichnus pedum, a worm burrow found in ancient rocks in Newfoundland, Canada. This tiny burrow marks one of the most important lines in all of geology.

Question 4

Are we in the Phanerozoic right now?

Accepted Answer

Yes, absolutely! The Phanerozoic is the current geologic eon, and it includes the present day. We are living in the Phanerozoic right now, specifically in its Cenozoic era, within the Quaternary period, in an epoch called the Holocene. The Phanerozoic is still ongoing and will continue until either a dramatic change in life on Earth or until geologists decide a new eon has begun.

Question 5

What are the three eras of the Phanerozoic?

Accepted Answer

The Phanerozoic is divided into three eras. The first is the Paleozoic, meaning ancient life, which ran from 538.8 to 251.9 million years ago and includes famous periods like the Cambrian, Devonian, and Permian. The second is the Mesozoic, meaning middle life, which ran from 251.9 to 66 million years ago and is the age of dinosaurs. The third is the Cenozoic, meaning recent life, which covers 66 million years ago to today and is the age of mammals.

Question 6

How long is the Phanerozoic eon?

Accepted Answer

The Phanerozoic eon spans approximately 538.8 million years, from its beginning to the present day. That is an almost incomprehensibly long stretch of time. To put it in perspective, if you stacked 538.8 million one-dollar bills, the pile would reach more than halfway from Earth to the Moon. And yet the Phanerozoic only accounts for about the last 12 percent of Earth's entire 4.5-billion-year history.

Question 7

What came before the Phanerozoic?

Accepted Answer

Before the Phanerozoic comes the Precambrian, a vast stretch of time covering roughly 4 billion years from Earth's formation to 538.8 million years ago. The Precambrian is divided into three eons: the Hadean, the Archean, and the Proterozoic. Life existed during much of the Precambrian, mostly as single-celled microbes and later as simple soft-bodied creatures, but it left far fewer fossils than the life of the Phanerozoic.

Question 8

How many mass extinctions happened in the Phanerozoic?

Accepted Answer

Scientists have identified five major mass extinctions during the Phanerozoic, collectively called the Big Five. These occurred at the end of the Ordovician, the Late Devonian, the end of the Permian, the end of the Triassic, and the end of the Cretaceous. The deadliest was the end-Permian extinction around 252 million years ago, which wiped out roughly 96 percent of all marine species and is sometimes called the Great Dying. The most famous is the end-Cretaceous extinction 66 million years ago that killed the non-avian dinosaurs.

Question 9

What was the Cambrian Explosion and how does it relate to the Phanerozoic?

Accepted Answer

The Cambrian Explosion marks the very opening chapter of the Phanerozoic, beginning around 538.8 million years ago. In a relatively short time, geologically speaking, nearly all the major animal body plans we know today appeared in the fossil record for the first time. Animals evolved eyes, legs, shells, and complex body structures almost simultaneously by geological standards. It is the event that defines why the Phanerozoic exists as a separate eon, because it is when animals became complex, hard-bodied, and visible in the rock record.

Question 10

Who discovered or named the Phanerozoic?

Accepted Answer

The term Phanerozoic was coined by American geologist George Halcott Chadwick in 1930. He chose Greek roots meaning visible animals to contrast this eon with the Precambrian, where life existed but left little fossil evidence. The concept of separating the time of obvious animal life from earlier Earth history had been developing among geologists throughout the 1800s, but Chadwick gave it the specific name that scientists still use today.

Question 11

Why does the Phanerozoic start with the Cambrian and not earlier?

Accepted Answer

The Phanerozoic starts at the Cambrian because that is when animals began producing hard parts like shells, bones, and mineralized skeletons that preserve well as fossils. Life existed before this, including the soft-bodied Ediacaran creatures of the late Precambrian, but those organisms left only rare and ambiguous impressions. The base of the Cambrian represents a sharp increase in the diversity and preservability of animal life, making it a natural and scientifically meaningful place to draw the boundary of a new eon.

Question 12

What periods are inside the Phanerozoic?

Accepted Answer

The Phanerozoic contains 12 geological periods in total. In the Paleozoic era, these are the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. In the Mesozoic era, they are the Triassic, Jurassic, and Cretaceous. In the Cenozoic era, they are the Paleogene, Neogene, and Quaternary. Each period is defined by its own unique set of life forms, climate conditions, and rock formations found around the world.

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