The Fossil Record of Viruses Welcome to another episode on the fossil record
with me Benjamin Burger. This is a special episode, as I’ve not been
able to post my normal weekly videos, since I’ve been quarantined because of the 2020
outbreak of the Covid-19 virus, which has made thousands of people sick around the world
the last few weeks. With schools all moving to online systems,
I’ve been in the front lines of helping faculty and teachers migrate courses fully
online, as well as my own courses which I typical teach with students in a classroom. I’ve had to cancel fieldtrips, scientific
conferences and readjust my whole life over the last few days. This disruption was all caused by a tiny,
a super tiny organism, which may not even be a living creature, but a few strains of
RNA that works really good at hijacking our cells in our lungs. Today I thought we could take a look at viruses:
what they are, where they came from and how have they evolved, and do they have a fossil
record? First what is a virus? Almost all life on the planet is composed
of cells, which are classified as either prokaryotic cells (bacteria), that is cells without organelles,
and eukaryotic cells (cells with organelles and a nucleus, which includes plants, fungus,
algae, and animals, including all the multicellular organisms). Virus are not in either of these two groups,
but something very bizarre, and very very tiny. Viruses exist as a particle or virions that
contain strands of DNA or RNA that can make proteins, surrounded by a protein coat or
capsid that protects the DNA or RNA from oxidation (that is reacting to oxygen that would break
apart those molecules), they can also be encased in some lipids or other proteins. Viruses can be shaped from helical forms to
shapes like a d20 dice from Dungeons and Dragons, or just be spherical in shape. Individual viruses are super tiny, about 100
times smaller than bacteria. This makes finding fossil viruses very challenging
since they are so small they can’t be seen even under optical microscopes, you would
need a specialized Scanning Electron Microscope to even see them. Likely, virus have been on the planet for
billions of years, and their ecology suggests that they may be remnants of the some of the
earliest life forms on the planet. But are viruses living creatures? Not exactly. Viruses don’t grow or eat, and they lack
metabolism, and they also don’t sexually reproduce. They can only replicate within a host cell. Viruses are everywhere, but especially in
the oceans. Most viruses are pretty harmless, but their
origin is very fascinating, and may explain why they can be so dangerous to us today. There are three theories to their origin. One theory holds that virus originated from
single cell bacteria. Bacteria reproduce by asexually splitting
their cells into two, by making a copy of the DNA in the cell. This works great to quickly reproduce when
there is food and good conditions to grow, but presents a problem because asexual reproduction
or clones of bacteria lack genetic diversity, and they don’t evolve or change quickly
enough to adapt to a changing environment. One adaptation that bacteria developed was
the ability to share genetic information between cells by replicating the DNA or RNA in their
cell, and sending this smaller package of information to other cells which would incorporate
this information into their own cell, actually putting it in their own DNA. This is like a network communication system. The problem with this system would be if a
bacteria cell produced a package of DNA or RNA that instead of being beneficial to the
cell, it would instead infect it, causing the cell to start replicating other packages
of DNA or RNA encoded to infect other cells. Just like viruses on a computer network can
cause issues by infecting a computer and sending emails to all your contacts in your email
account with copies of the virus, and spread quickly. True viruses in nature likely caused considerable
damage among early colonies of bacteria on the planet. These packages of DNA or RNA would have originated
from bacteria, and but quickly spread, as they replicated in cells that they infected. This theory of origin is called the Escape
Hypothesis. The second theory is that viruses may have
originated as the most primitive life form on the planet, during a period of time in
the Archean or even Hadean, about 4 billion years ago. When the atmosphere and ocean’s lacked oxygen,
and the world was much warmer. The RNA-world of this time period may have
existed in oceans which were filled with self-replicating particles of RNA that would survive on a planet
with-out oxygen, but rich in methane and other hydrocarbon molecules. Scientists have postulated that these ancient
viruses would consist solely of single strains of RNA. RNA is ribonucleic acid, a nucleic acid that
in living cells act as a messenger carrying instructions from DNA to synthesize proteins
needed in the cell, some viruses consist only of RNA. An RNA-World would be a world where these
ribonucleic acids would utilize hydrocarbon molecules to replicate new strains of RNA. RNA is an enzyme and can catalyze chemical
reactions very quickly. With the emergence of bacteria, these RNA
strains of early viruses may have developed the ability to infect these early cells. This theory of origin is called the Virus-First
Hypothesis. The third theory is that viruses may be simply
bacterial cells that have retrograded into simpler lifeforms. Many viruses like those that cause small pox
are composed of DNA, and are relatively speaking large in size. These DNA viruses could just be specialized
bacteria that developed a parasitic lifestyle by utilizing other cells for replication. Giving up the ability to grow and eat, and
developing a host-parasite relationship with other organisms. This theory of origin is called the Regressive
Hypothesis. It is likely that all these hypothesizes are
true, with various viruses originating from one of these processes. The influenza virus particles contain only
RNA, and are very tiny about 80 nanometers in diameter, and if we don’t know how they
originated, do we know something about how they evolve and change over time? Viruses change by mutations in the RNA which
can result during the replication process within infected cells. A base-pair change can lead to a change in
the genetic makeup of the strand of genetic material within the virus. One of the issues with viruses is when these
mutations in the genetic code allows the virus to infect a new host. This is thought to happen with many pandemics,
in which a virus that infects one animal, develops a mutation that allows it to infect
humans. When an animal is infected with a virus, millions
to billions of copies of the virus are made, and there can be little mistakes in the code
of the virus that allow it to jump to a different host if the opportunity arises. It also means that with the numbers of replications
of viruses made in a host, that viruses can change very quickly, and if these changes
are advantageous they can spread very fast within host cells, and between individuals. Scientists can de-code the genetic material
within these viruses, and develop phylogenies that are based on these mutation events, giving
an evolutionary tree that helps map out the spread of the virus from one host to another. As a host, humans can also host this mutation
event within their own cells, such that a pandemic can stem from a single individual
unknowingly. Virologists are studying the origin of this
particular strain of the influenza virus, called the severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2), which is provisionally called the 2019 novel coronavirus, or COVID-19,
a single strain RNA virus. Phylogenetic study of the virus suggests a
close relationship to viruses that also infect bats and pangolins. Pangolins may have been the cause of this
virus, as they been imported into China and present in the market where this virus was
thought to have originated from. The COVID-19 virus infects lung tissue, that
is individual cells in the lungs of mammals which are more sensitive to these viruses
because of the importance they serve in the exchange of oxygen and carbon dioxide in respiration
when we breath. Hence, the virus can damage these cells and
cause rapid onset of health issues related to respiration. Viruses spread from person to person by coughs
and particles that get breathed in. Each time a virus infects a person, the virus
also change with further mutations, such that viruses maybe become more benign over time,
as those viruses that jump from person to person, made more likely if did not make the
person sick enough to stay home. The best protection for infection is a quarantine
or isolation, or social distancing. I’m not a virologist or infection diseases
expert, but a paleontologist. So has anyone found a fossil virus? Yes, they have! A study from 2005 by George and Roberta Poinar,
published in the Journal of Invertebrate Pathology found evidence for fossil viruses. They found a fossil midget preserved in amber,
that exhibited an infection of the cypovirus. This evidence of a fossil virus comes from
the 99 million year old Burmese amber, that has also has preserved this tiny lizard that
to be a dinosaur/bird recently described this year. But these viruses are so tiny they can’t
be directly be observed, instead the pathology exhibited in the fossil midget suggests the
presence of the virus. Hence fossil evidence of viral infections
extends back to the age of dinosaurs, but what about earlier in Earth’s history? In 2010, James Laidler and Kenneth Stedman
did a cool experiment published in Astrobiology to see if they could fossilize a virus in
silica, such as would be likely in conditions in hydrothermal springs. They were successful in fossilizing a modern
virus in this solidified silica rock, suggesting that viruses could be found in chert or silica
veins from early in Earth’s history. Hence, there is the possibility that viruses
could be found in the future from early in Earth’s history, which would support their
long presence on Earth today. It also suggests that viruses, if present
on other planets could also be preserved in the rocks. These fossil viruses can be detected in silica,
by using an energy-dispersive X-ray spectrophotometry (EDS), looking for the element phosphorus,
which is an element found within RNA and DNA. Phosphorus is rare in silica, and tests could
be developed in the future to be able to detect phosphorus in silica rocks, as well as carbon
isotopes to detect fossil viruses that cannot be easily seen under a microscope. I hope that this video reaches you while you
are safe and healthy. I going to try and upload more videos in the
coming weeks despite all the quarantines across the world, because it is nice to have some
educational videos to watch during this time of uncertainty. I also want to thank my patreons for the support. I’m going to be back to my normal schedule
soon, and have some interesting videos planned for the future on fossils, dinosaurs and geology,
now that the snow is nearly melted away. I’m looking forward to getting back in the
field. I hope the future holds a healthy outcome
for you and your entire family.
