1. What Tiny Spores Reveal About the Oldest Land Plants
The oldest widely accepted fossil evidence for land plants comes from tiny spores found in layers of rock from the Middle Ordovician period, about 475 million years ago [1]. Spores are dust-like particles that plants release to reproduce. These specific spores may have come from early plants related to mosses. However, researchers have only found the spores themselves, not the actual body of the plant that produced them.
2. How Molecular Clocks Date Plants Earlier Than Fossils Do
A molecular clock is a method that estimates when species branched apart by measuring the amount of difference in their genes. It is like calculating when a candle was lit based on how much wax has burned away. If the candle burns at an unsteady rate, the time estimate is off. A 2018 study estimated that the origin of all land plants occurred between the Middle Cambrian and Early Ordovician periods. It also estimated that vascular plants, which have channels for water in their roots and stems, originated between the Late Ordovician and Silurian periods [2]. Both of these estimated dates are older than the spore fossils mentioned earlier.
These numbers are estimates shown as ranges. Just because fossils are missing from a certain time period does not mean plants were not there. Conversely, these estimates are not confirmed dates. The gap between the two types of clues is a subject that scientists are still investigating.
3. Cooksonia: A Small Early Land Plant With No Roots or Leaves
Cooksonia is known as the oldest fossil of a vascular plant where the body structure is clear. It has been found in Silurian rock layers in places like Wales, United Kingdom. Cooksonia was only a few centimeters tall. It had no roots, leaves, or flowers. Instead, it had branching stems with sacs at the tips that held spores [3]. The date of these fossils varies by source, ranging from about 433 million to 393 million years ago. Saying it was a "grass-like plant from hundreds of millions of years ago" is the most accurate description.
Not all Cooksonia species were the same. Some had stomata, which are openings for air exchange. Some had dark lines that look like water-transporting tissue. Other species did not have this tissue [3]. The ways of living on land differed among Cooksonia species.
4. The Rhynie Chert: A Scottish Rock That Preserved a Whole Ecosystem
The Rhynie Chert in Scotland is a rock from about 407 million years ago (Early Devonian). It preserves plants, arthropods, fungi, and microbes together. It is considered one of the best-preserved examples of an early land ecosystem [4]. It is not "the first ecosystem," but rather a very well-preserved early example. Slight changes in the terrain of a floodplain allowed environments ranging from dry land to fresh water. Along with land arthropods, the dormant eggs of small crustaceans that lived in fresh water are also preserved [4].
Fungi are found inside the cells of the plants in the Rhynie Chert. These structures suggest that fungi and plants exchanged nutrients. Two possible groups of fungi have been reported [5]. Previously, one group was thought to be the ancestral partner, but this view is now being questioned. The existence of evidence for symbiosis is different from the claim that fungi helped plants move onto land. The latter has not yet been proven.
5. How Arthropod Footprints Show Early Animal Life on Land
Footprints of arthropods are a separate clue from plant fossils for when life moved onto land. In 2002, researchers reported arthropod footprints in Canadian sandstone from the Cambrian to Ordovician periods. This pushed back the record of the first steps onto land by up to 40 million years [6]. However, footprints might represent short visits rather than permanent residence. The dates also have a range.
The title of the oldest air-breathing land animal is under debate. The Scottish millipede *Pneumodesmus* has spiracles, which are openings for breathing air. It was long considered the oldest example of an air-breathing land animal, dated to about 428 million years ago (Silurian) [7]. A 2017 study that re-measured the age of the rock layer gave a date of about 413.7 million years ago (Early Devonian, with an error margin of plus or minus 4.4 million years). Reports said it lost its title [8]. However, a 2023 review dated the layer to the Late Silurian [11]. Scientists are still divided on which date is correct.
6. Rhyniognatha: The Jaw Fossil Identified as the Oldest Insect
In the Rhynie Chert, a fossil consisting only of a large jaw (named *Rhyniognatha*) was found. In 2004, it was identified as the oldest insect, estimated to be between 396 million and 407 million years old. However, a 2017 re-examination noted that newly visible structures did not match insects. It is more likely a myriapod, perhaps related to centipedes [10]. The name "oldest insect" is currently under debate.
Genetic analysis suggests an even older origin for insects. A 2014 analysis using 1,478 genes estimated that insects originated in the Early Ordovician period, about 479 million years ago. It estimated that the ability to fly originated in the Early Devonian, about 406 million years ago [9]. These dates are older than the fossils, but they are just one estimate among others.
7. How You Can Look for Spore-Bearing Mosses Yourself
You can try looking for mosses in parks or by the roadside. Check if there are small sacs growing at the tips, which hold spores. A magnifying glass helps you see the fine details. This makes the story of spores becoming the oldest fossil evidence feel closer to home. When looking closely at the ground, be careful of your footing and any insects nearby. You can also find books about paleontology in libraries to read about how fossil dates are determined. Comparing two books to see if they describe the same fossil dates differently is also recommended.