Biodiversity Notes – Sept. 26/12
- The origins of plants: Proterozoic eon (2BYA) – first eukaryotic cells. Middle Proterozoic (1BYA) –
first multicellular plants – green algae. Late Proterozoic (630MYA) – first animals. The oceans were
very important in the evolution of life on earth – the first plants (green algae), animals, and probably
fungi (don’t fossilize easily so hard to know) were marine. The Proterozoic eon occurred before the
Paleozoic era. The Paleozoic era, which consists of the Cambrian, Ordovician, Silurian, Devonian,
Carboniferous, and Permian periods, is part of the Phanerozoic eon. The Mesozoic era is after the
Paleozoic era, and it consists of the Triassic, Jurassic, and Cretaceous periods.
- Paleozoic – Ordovician Period (began 480MYA): The Paleozoic era lasted 300 million years and lots
of evolution and diversification occurred. The first part of the Paleozoic era was the Cambrian period,
but this was not an important time for diversification of plants, only animals. Just probably green alga
was around. During the Ordovician period, the colonization of land by plants and animals occurred
about 450MYA. The first land plants mostly likely had symbioses with fungi. This is because they
were simple and maybe didn’t have roots, so the fungi provided them with nutrients and helped
them evolve. The taxa of the first land plants is extinct, but they resemble extant mosses and
liverworts in some characteristics, such as they are non-vascular, they require wet environments,
and they have limited size.
- Paleozoic – Silurian Period (began 440MYA): The first vascular plants are in the fossil record. The
vascular system is the presence of more complex tissues, like xylem and phloem. These are fluid-
conducting tissues that also provide structure. Xylem conducts water and some nutrients, and is the
woody part. Phloem conducts synthates or products of photosynthesis. The evolution of the vascular
system allowed plants to adapt and move to dry land. Adaptation is the evolutionary process which
takes place over many generations, whereby a population/species becomes better suited to its
habitat. An adaptation is a morphological structure or behaviour. These plants no longer needed
water for support, allowing them to colonize dryer habitats and grow larger in size.
- Paleozoic – Devonian Period (began 420MYA): There was land plant diversification and ferns and
seed plants. A seed plant is an embryonic plant enclosed in a case. The case allows for adaptation to
dry land by preventing desiccation (drying out). Greening of the continents occurred during this time
– forests of primitive/basal vascular plants appeared. Plants are dependent on soil and at this time,
soil was well developed. Soil allowed for the evolution of bacteria, algae/unicellular eukaryotes,
fungi, non-insect arthropods, and the first insects.
- Paleozoic – Carboniferous Period (began 360MYA): There were extensive swamps and forests with
massive trees (relatives of extant lycophytes and horsetails). Large quantities of wood were buried
underwater, anaerobic decomposition occurred, and over time formed into coal. Fossil fuels are coal,
oil, and natural gas. All fossil fuels are formed from the fossilized remains of dead organisms, mostly
plants. We are dependent on fossil fuels to heat our homes, run our vehicles, power industry, and
provide electricity. Humans have a great dependence on live and dead organisms.
- Paleozoic- Permian Period (began 300MYA): Seed plant diversification occurred, resulting in
conifers. The end-Permian mass extinction caused 95% of life to become extinct. Plants were not
really affected by this extinction, it was mostly marine invertebrates and insects.
- Mesozoic – Triassic and Jurassic Periods (began 250MYA): Conifers and ferns dominated.
- Mesozoic – Cretaceous Period (began 150MYA): Flowering plants (angiosperms) appeared in the
fossil record and diversified. Most major extant land plants groups were around at this time. There
was co-evolution of plants with pollinating insects and other animals. Insects are primary pollinators.
- Importance of plants today: There are 300,000 described species. Plants are involved in
photosynthesis, the carbon cycle, carbon fixation (carbon is taken out of the atmosphere and fixed into organic compounds in plant tissue), and climate change. Plants are a carbon sink, which means
they take gaseous forms of carbon from the atmosphere and they fix them in their tissues.
Photosynthesis involves carbon fixation. Autotrophs make their own food by fixing carbon. Cutting
down forests removes carbon si