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1. The disappearance of methane and ammonia from the Earth's atmosphere and the
presence of nitrogen, hydrogen, and oxygen can be attributed to a process known as
photodissociation. Photodissociation is a chemical process that occurs when a molecule
absorbs a photon of light, causing it to break apart into smaller molecules or atoms. In
the case of methane (CH4) and ammonia (NH3) in the Earth's atmosphere, they are both
susceptible to photodissociation by ultraviolet (UV) radiation from the sun. When
methane molecules absorb UV radiation, they break apart into carbon dioxide (CO2) and
water (H2O) molecules: CH4 + 2O2 → CO2 + 2H2O. The carbon dioxide and water
molecules are then further broken down into oxygen (O2) and hydrogen (H2) atoms
through additional photodissociation: CO2 + hν → CO + O. H2O + hν → H + OH. In the
case of ammonia, it can also be photo dissociated by UV radiation to form nitrogen (N2)
and hydrogen (H2) molecules: NH3 + hν → N2 + 3H2. Over time, the process of
photodissociation has resulted in the accumulation of nitrogen, hydrogen, and oxygen in
the Earth's atmosphere, while methane and ammonia have become increasingly rare.
The presence of these gases in the atmosphere is crucial for supporting life on Earth, as
they are involved in many important biochemical processes.
2. It is possible for animals to have lived on ancient Earth before the emergence of green
plants, although the types of animals that would have existed in such an environment
would have been different from those that we are familiar with today. The earliest
forms of life on Earth are thought to have been single-celled organisms that lived in the
oceans, such as cyanobacteria. These organisms were able to carry out photosynthesis
and produce oxygen as a byproduct, which gradually led to the oxygenation of the
Earth's atmosphere. However, it took several hundred million years for oxygen levels to
rise to the point where they could support more complex life forms. During this time,
simple animals such as sponges and jellyfish likely existed in the oceans, feeding on
organic matter and other small organisms. These early animals would have had to rely
on other sources of energy besides photosynthesis, such as chemosynthesis or feeding
on organic matter produced by bacteria. It's also possible that they may have been able
to absorb nutrients directly from the water or sediment. Eventually, as oxygen levels
continued to rise, more complex animals evolved, such as worms and arthropods. The
emergence of plants, including green plants, provided a new source of energy in the
form of photosynthesis, which helped to support the development of larger and more
diverse animal life.
3. If the ozone layer continues to decrease due to the release of certain chemicals into the
atmosphere, it could have significant impacts on living things on Earth. The ozone layer
in the stratosphere serves as a shield that protects the planet from harmful ultraviolet
(UV) radiation from the sun. If the ozone layer continues to decrease, more UV radiation
will reach the Earth's surface, which can have several negative impacts on living things:

Skin damage and cancer: Increased UV radiation can cause skin damage and
increase the risk of skin cancer in humans and animals that are exposed to it.
This can lead to health problems and a decrease in overall fitness and
reproductive success.

Reduced crop yields: Increased UV radiation can also damage plants and reduce
crop yields, negatively impacting food security and the global economy.

Disruption of ecosystems: Increased UV radiation can also disrupt ecosystems by
altering the balance of species and reducing the productivity of certain
organisms, such as phytoplankton, which form the base of the marine food web.

Increased air pollution: Some air pollutants, such as nitrogen oxides, can also
break down ozone in the atmosphere, exacerbating the problem of ozone
depletion and leading to further negative impacts on living things.
Overall, a decrease in the ozone layer could have serious consequences for the health
and well-being of living things on Earth, from humans to animals and plants. It is
therefore important to take steps to reduce the release of chemicals that contribute to
ozone depletion and to continue to monitor the health of the ozone layer in order to
protect our planet's ecosystem.
Padlet: https://padlet.com/kumarv23/timeline-activity-544a15zsj09jvngi