What 3 Secrets About Ancient Earth Are Hidden in Marine Fossils?

TL;DR

Marine fossils reveal ancient water temperatures, ocean depths, and the length of Earth’s day. Isotope and magnesium levels preserve temperature clues, foram communities trace habitats as deep as 2000 meters, and shell growth cycles show that a day 70 million years ago lasted 23.5 hours. Read on to see how scientists extract these environmental records from shells and skeletons.

Transcript

earth's fossil record is loaded with the remains of ocean creatures but ancient life didn't exist in a vacuum and a key part of understanding these species is understanding the environments they lived in fortunately there's more to paleontology than just identifying old dead stuff fossils can also provide clues to the conditions those species lived... Read More

Key Insights

• "The key is, marine critters inherit that ratio when they build their bodies, so paleontologists can measure the ratio of isotopes in fossils to calculate ancient water temperature." (1:22)
• "Like, there’s another field called paleobathymetry, which uses things like fossils to study ancient water depths." (2:31)
• "And since models tell us that the length of a year hasn’t changed, that means that each day back then was only 23.5 hours long!" (4:48)
• "And it showed that about 430 million years ago, there were about 21 hours per day!" (5:00)

Questions & Answers

Q: What can marine fossils reveal about ancient Earth?

Marine fossils can reveal ancient water temperatures, water depths, and the length of a day. These clues help paleontologists reconstruct the environments in which ancient organisms lived.

Q: How do fossils reveal ancient ocean temperatures?

Marine organisms inherit the local ratio of oxygen-16 to oxygen-18 when building shells or skeletons. Paleontologists measure that isotope ratio in fossils to calculate ancient water temperature.

Q: Why does magnesium in fossils indicate water temperature?

Some marine organisms incorporate magnesium into their bodies through an endothermic reaction that requires heat. Warmer water therefore results in more magnesium being incorporated into their fossils.

Q: What did foraminifera reveal about temperatures over the past 50 million years?

A study from 2000 analyzed magnesium and oxygen in foraminifera shells to estimate global temperatures over the past 50 million years. It identified multiple cooling phases as Earth shifted from hothouse conditions without polar ice caps to modern icehouse conditions.

Q: What is paleobathymetry?

Paleobathymetry is the study of ancient water depths using evidence such as fossils. Scientists compare fossil foram communities with modern communities to judge whether a habitat was a shallow coast, deep bay, or abyss.

Q: What did fossils reveal about the sinking of New Zealand’s Waitemata Basin?

Fossil foram communities documented how the Waitemata Basin sank after tectonic shifts around 20 million years ago. Over several million years, it changed from flooded bays and inlets to shallow ocean, then reached waters as deep as 2000 meters.

Q: How can fossils show the length of an ancient day?

Researchers use sclerochronology to count daily growth layers inside larger seasonal layers in shells and corals. The number of daily cycles within a full seasonal cycle indicates how many days occurred in a year, allowing researchers to calculate the hours in each day.

Q: How long was a day 70 million years ago?

A study published in February 2020 counted 372 daily growth cycles in Late Cretaceous bivalve shells. Because the length of a year had not changed according to the models used, the researchers calculated that each day was 23.5 hours long.

Summary & Key Takeaways

• Fossils can provide insights into ancient temperatures by analyzing the ratio of isotopes in marine organisms' bodies, allowing paleontologists to calculate ancient water temperatures.

• Paleobathymetry, the study of ancient water depths, can be determined by comparing fossil foram communities with present-day communities, revealing changes in depth over time.

• Fossils have also been used to calculate the length of a day in the past, with marine fossils showing that days were shorter millions of years ago.