Microfossil

A microfossil is a tiny fossil, usually between one micrometre and one millimetre in size. Scientists use special tools called light or electron microscopy to study these small fossils. Fossils that can be seen without such tools, or with just a hand lens, are called macrofossils.

An enigmatic carbonaceous microfossil,Cochleatina canilovica, from the Late Ediacaran

Microfossils appear often in the geological record from very old times, like the Precambrian, up to the present day, known as the Holocene. They are most often found in places that were once oceans, but they can also be in areas that had salty, fresh, or even land water sedimentary deposits.

Almost every kind of life has left behind microfossils, but the most common ones come from tiny water creatures and their remains, such as protist skeletons or microbial cysts. These include groups like the Chrysophyta, Pyrrhophyta, Sarcodina, acritarchs, and chitinozoans. We also find pollen and spores from vascular plants in microfossil records.

Overview

A microfossil is a very small fossil that you can only see with a microscope. These fossils are usually smaller than 1 mm and can come from tiny sea creatures, plants, or even parts of bigger plants and animals like small teeth or seeds.

Microfossils are found in rocks and sediments all over the world. They help scientists learn about past climates and environments, and they can even help find oil and gas. Some of the oldest known microfossils were found in Canada and may be as old as 4.28 billion years, showing that life on Earth began very early after the planet formed.

Index fossils

Index fossils, also called guide fossils, indicator fossils or dating fossils, are the remains or traces of certain plants or animals from a specific time in Earth's history. They help scientists find out how old rocks are. To be useful, these fossils must come from a short time, be found in many places, and change quickly over time. When rocks far apart have the same index fossil, scientists know they are about the same age.

Scientists often use tiny fossils, called microfossils, to help date rocks. These include acritarchs, chitinozoans, conodonts, dinoflagellate cysts, ostracods, pollen, spores, and foraminiferans. Different fossils work best for different ages of rocks. The best fossils are found everywhere and lived only a short time. This makes it easier to know when the rocks were formed. Sometimes, scientists look at a group of fossils together instead of just one. This group can give an even more exact time frame for the rocks.

Composition

Microfossils from a deep sea sediment core

Microfossils can be grouped by what they are made of. Some are made of siliceous material, like diatoms and radiolaria. Others are made of calcareous material, such as coccoliths and foraminifera. Some are phosphatic, like parts of certain vertebrates, and others are organic, such as pollen and spores studied in palynology.

Organic-walled

Further information: Palynomorphs and Kerogen

Pollen has a special outer layer that helps it stay safe over time. We can find many pollen grains that have separated from the plants they came from. Scientists study pollen to learn about past plants and climates. Pollen first appears in the fossil record during the late Devonian period.

Late Silurian sporangium bearing trilete spores provide the earliest evidence of life on land.Green: spore tetrad. Blue: spore with Y-shaped trilete mark.Spores are about 30–35 μm across

A spore is a tiny part of a plant, algae, fungus, or other tiny organism that helps it reproduce. Spores can survive in tough conditions and move to new places.

Chitinozoa are tiny, flask-shaped fossils from the ocean. They were made by organisms we still don’t fully understand. They are common from the Ordovician to Devonian periods and are found all over the world in ocean sediments. Because they changed quickly, they help scientists date rocks.

Acritarchs are tiny fossils with uncertain origins, found from about 2,000 million years ago to today. They are made of carbon and come in many shapes and sizes. Their changes over time show important events in Earth’s history, like changes in plant life and climate.

A Late Silurian chitinozoan from the Burgsvik beds showing its flask shape

Cells from very early life can be preserved in rocks. Their walls turn into a special material called kerogen, which helps them stay safe. These tiny cells come in different shapes and sizes.

Mineralised

Further information: Shelled protists

Siliceous

Siliceous ooze is a special material on the deep ocean floor. It is made from the tiny skeletons of small sea creatures. It is mostly made of silica, a material from tiny sea plants and animals like diatoms and radiolarians. Silica is important in the ocean and moves around through the silica cycle. How far you are from land, how deep the water is, and how much food is in the ocean all affect how much silica is in the water.

[Diatomaceous earth](/wiki/Diatomaceous_earth) is a soft, rocky material made from the tiny shells of [diatoms](/wiki/Diatom)

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Silicoflagellate

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Radiolarian

Phytoliths are tiny, hard parts made of silica found in some plants. They stay even after the plant breaks down.

Calcareous

The word calcareous means something made from or containing a lot of calcium carbonate, a kind of mineral. This material is usually found in shallow water near land because the tiny sea creatures that make it need nutrients from the land. Calcareous ooze is made from the tiny remains of sea creatures and builds up on the sea floor. This only happens in water that is not too deep, because in very deep water the calcium carbonate dissolves.

Illustration of a _[Globigerina](/wiki/Globigerina)_ ooze

Shells ([tests](/wiki/Test_\(biology\))), usually made of calcium carbonate, from a [foraminiferal](/wiki/Foraminifera) ooze on the deep ocean floor

Siliceous ooze
mineral forms	protist involved	name of skeleton	typical size
SiO₂ silica quartz glass opal chert	diatom	frustule	0.002 to 0.2 mm	diatom microfossil from 40 million years ago
SiO₂ silica quartz glass opal chert	radiolarian	test or shell	0.1 to 0.2 mm	elaborate silica shell of a radiolarian

Calcareous ooze
mineral forms	protist involved	name of skeleton	typical size
CaCO₃ calcite aragonite limestone marble chalk	foraminiferan	test or shell	many under 1 mm	Calcified test of a planktic foraminiferan. There are about 10,000 living species of foraminiferans
	coccolithophore	coccoliths	under 0.1 mm	Coccolithophores are the largest global source of biogenic calcium carbonate, and significantly contribute to the global carbon cycle. They are the main constituent of chalk deposits such as the white cliffs of Dover.

Ostracods

Ostracods are tiny creatures found everywhere, often called seed shrimps. They have flat bodies and are protected by a shell. Most ostracods are about the size of a small seed.

Conodonts

Scolecodonts

Scolecodonts are tiny jaws from a type of worm called polychaete annelids. These worms have lived in many oceans for over 500 million years. Their jaws are made of strong material and are often found as fossils in very old rocks from the Cambrian time. Because the worms themselves are soft and rarely become fossils, their jaws are the main clue we have about these worms from long ago. Scolecodonts are very small, usually less than 1 mm, which makes them a type of microfossil. They are often found with other tiny fossils, but sometimes they are the only fossils in certain sediments.

Cloudinids

The cloudinids were an early group of animals that lived a very long time ago, about 550 million years ago, during the late Ediacaran period. They went extinct at the start of the Cambrian period. Cloudinids made small, cone-shaped fossils from a substance called calcite. These cones were nested inside each other like funnels.

Cloudinids have been found in many places around the world. Scientists are not sure exactly how they lived. Some think they may have grown on layers of tiny water organisms called microbial mats. But we do not know for sure. Scientists also are not sure if cloudinids were a type of worm or another kind of simple animal. Recent studies suggest they might have had a simple body plan like other early animals.

Cloudinids are important because they are among the first small fossils to have hard parts. This helps scientists learn about how animals first began to develop hard shells or skeletons. Some fossils show marks that look like they were made by predators. This suggests that animals may have developed hard shells to protect themselves. This idea is thought to have helped cause a big increase in animal life called the Cambrian explosion.

Dinoflagellate cysts

Some tiny living things called dinoflagellates create special resting stages called dinoflagellate cysts or dinocysts. These cysts are usually between 15 to 100 micrometres in size and are found in sediments as microfossils. They have strong walls made of a material called dinosporin, and some are made from calcium or silica.

Dinocysts are made by some dinoflagellates when they are resting. These cysts are found in many species of dinoflagellates, both in freshwater and in the ocean. Scientists have found evidence that dinocysts have been around since the Early Cambrian period.

See also: Microbial cyst and Dinoflagellate § Dinoflagellate cysts

Sponge spicules

Main article: Sponge spicule

Spicules are tiny parts that help most sponges stay standing and protect them. When many spicules fit together, they make the sponge's skeleton.

Very small spicules, so tiny you need special tools to see them, can become microfossils. These are called microscleres. Bigger spicules that you can see without help are called megascleres. Spicules can be made from different materials, like calcareous or siliceous substances, or from a special material called spongin. They come in many shapes and patterns.

Freshwater sediments

Marine sediments

Main article: Marine sediments

Further information: Paleoceanography, Paleoclimatology, and Marine isotope stage

Sediments at the bottom of the ocean come from two main places: land and tiny sea creatures. Land sediments, called terrigenous sediments, come from rocks on land that are worn away by rivers, wind, volcanoes, or glaciers.

The other part of ocean sediment comes from the remains of tiny sea creatures, called biogenous sediments. These tiny creatures leave behind skeletons when they die. Some of these sediments are called "ooze" because they come from these tiny sea creatures.

Micropaleontology

Main article: Micropaleontology

The study of tiny fossils is called micropaleontology. These small fossils are little creatures or small parts of bigger ones. Because they are found almost everywhere and don't break down easily, microfossils help scientists learn about old rock layers. They are also useful for understanding past environments because they change in predictable ways when conditions around them change.