How Many Mass Extinctions Have There Been?

TL;DR

The famous "Big Five" mass extinctions may not be the only major extinction events in Earth's history, and the fossil record is inconsistent in capturing the full extent of past life.

Transcript

In the 1970s, a scientist named Jack Sepkoski embarked on the most ambitious fossil hunt ever – but instead of digging in the dirt, he dug through dusty piles of academic research and scraped together a record of all the ocean-dwelling creatures known to science. It was tedious work, but the data it yielded gave rise to perhaps the most famous char... Read More

Key Insights

• 💆 The "Big Five" mass extinctions may not be the only significant mass extinctions in Earth's history.
• 🍃 The Great Oxygenation Event had a major impact, but its victims were microscopic and left no fossil record.
• 👨‍🎤 The fossil record is incomplete and biased, with more fossils found in certain types of environments and periods with more rocks.
• 💆 Adjusting for inconsistencies in the fossil record suggests there may have been eight major mass extinctions.
• 💆 Some mass extinctions alter the evolutionary tree more drastically than others, shaping the course of life on Earth.
• 🫵 The fossil record does not provide a comprehensive view of all past life on Earth.
• 💆 The number of mass extinctions is somewhat arbitrary due to the challenges of interpreting the fossil record.

Questions & Answers

Q: Were there mass extinctions other than the "Big Five"?

Yes, there may have been additional major mass extinctions in Earth's history, including the Great Oxygenation Event and potentially others not yet identified.

Q: Why does the fossil record become less complete the further back in time we go?

Various factors contribute to the incomplete fossil record, including preservation biases towards swampy environments and periods with more rocks. Additionally, the fossil record captures a different fraction of life from one period to the next.

Q: How do paleontologists adjust for inconsistencies in the fossil record?

Paleontologists use statistical methods to account for biases and inconsistencies in the fossil record, allowing them to estimate diversity more accurately. The latest diversity curve suggests there may have been eight major mass extinctions.

Q: Do all mass extinctions have the same impact on the tree of life?

No, some mass extinctions prune away a large number of species but leave the major branches of the evolutionary tree intact. Others can reshape the tree more drastically, decimating previously thriving branches and preparing others for dominance.

Summary & Key Takeaways

• Jack Sepkoski compiled data on ocean-dwelling creatures, leading to the identification of the "Big Five" mass extinctions.

• The Great Oxygenation Event poisoned oxygen-hating microbes but left no fossil record.

• The fossil record is incomplete and inconsistent, making it challenging to accurately tally the number of species and determine the extent of mass extinctions.